Publications
2025
The surface tension of partially wetting droplets deforms soft substrates. These deformations are usually localized to a narrow region near the contact line, forming a so-called 'elastocapillary ridge.' When a droplet slides along a substrate, the movement of the elastocapillary ridge dissipates energy in the substrate and slows the droplet down. Previous studies have analyzed isotropically spreading droplets and found that the advancing contact line 'surfs' the elastocapillary ridge, with a velocity determined by a local balance of capillary forces and bulk rheology. Here, we experimentally explore the dynamics of a droplet sliding across soft substrates. At low velocities, the contact line is nearly circular, and dissipation increases logarithmically with speed. At higher droplet velocities, the contact line adopts a bullet-like shape, and the drag force levels off. At the same time, droplets shed a pair of 'elastocapillary rails' that fade away slowly behind them. These results suggest that sliding along the parallel edges of a bullet-shaped droplet dissipates less energy than surfing the wetting ridges at the front and back.
2024
- Amino acids modulate liquid-liquid phase separation in vitro and in vivo by regulating protein-protein interactionsXufeng Xu, Aleksander Rebane, Laura Roset Julia, Kathryn A. Rosowski, Eric Dufresne and Francesco StellacciProceedings of the National Academy of Sciences of the United States of America, vol. 121: no. 50, pp. e2407633121, National Academy of Sciences, 2024.
Liquid-liquid phase separation (LLPS) is an intracellular process widely used by cells for many key biological functions. It occurs in complex and crowded environments, where amino acids (AAs) are vital components. We have found that AAs render the net interaction between proteins more repulsive. Here, we find that some AAs efficiently suppress LLPS in test tubes (in vitro). We then screen all the proteinogenic AAs and find that three specific AAs, including proline, glutamine, and glycine, significantly suppressed the formation of stress granules (SGs) in U2OS and HeLa cell lines (in vivo) irrespective of stress types. We also observe the effect in primary fibroblast cells, a viable cell model for neurodegenerative disorders. Kinetic studies by live-cell microscopy show that the presence of AAs not only slows down the formation but also decreases the saturating number and prevents the coalescence of SGs. We finally use sedimentation-diffusion equilibrium analytical ultracentrifuge (SE-AUC) to demonstrate that the suppression effects of AAs on LLPS may be due to their modulation in protein-protein and RNA-RNA interactions. Overall, this study reveals an underappreciated role of cellular AAs, which may find biomedical applications, especially in treating SG-associated diseases.
- Dehydration drives damage in the freezing of brittle hydrogelsShaohua Yang, Dominic Gerber, Yanxia Feng, Nicolas Bain, Matthias Kuster, Laura De Lorenzis, Ye Xu, Eric Dufresne and Robert StyleScience Advances, vol. 10: no. 34, pp. eado7750, AAAS, 2024.
It is widely known that freezing breaks soft, wet materials. However, the mechanism underlying this damage is still not clear. To understand this process, we freeze model, brittle hydrogel samples, while observing the growth of ice-filled cracks that break these apart. We show that damage is not caused by the expansion of water upon freezing or the growth of ice-filled cavities in the hydrogel that exert pressure on the surrounding material. Instead, local ice growth dehydrates the adjacent hydrogel, leading to drying-induced fracture. This dehydration is driven by the process of cryosuction, whereby undercooled ice sucks nearby water toward itself, feeding ice growth. Our results highlight the strong analogy between freezing damage and desiccation cracking, which we anticipate being useful for developing an understanding of both topics. Our results should also give useful insights into a wide range of freezing processes, including cryopreservation, food science, and frost heave.
- Dynamics of Wetting and Adhesion on Soft SubstratesKatrina Smith-MannschottDoctoral Thesis, Zurich, ETH Zurich, 2024.
The ubiquity of soft materials in our daily experiences, in addition to their growing importance in industrial applications, makes understanding their behavior of great interest. As research into contact between material interfaces shifted more towards compliant materials, it became clear that their behavior during contact differed from that of stiffer materials. The classical continuum mechanics model that had originally been developed for more rigid materials, needed to be augmented to include adhesive forces in order to explain the contact mechanics of these softer solids. However, as increasingly compliant solids came under study, it became evident that even this updated model was not quite able to accurately capture the geometry and force of contact. Further research showed that for very soft substrates, surface stress plays a vital role in determining contact behavior. Even with this progress, the area of contact mechanics of soft solids continues to be one rife with questions, in which we are still working to understand the deep fundamentals. This dissertation contributes to the field by exploring two aspects of contact mechanics of soft solids: (i) the effect of stretching a soft substrate on wetting at its surface and (ii) the dynamics of contact initiation. In the first part of this thesis, we use polydimethylsiloxane (PDMS) gels to establish that stretched, soft, smooth solids exhibit anisotropic wetting behaviors, contrary to expectations from our existing continuum mechanics model of contact behavior. We observe this anisotropy in static droplets of varying sizes, with smaller droplets exhibiting greater eccentricity than larger ones. Additionally, we show that the eccentricity of the droplet shape grows monotonically with the stretch applied to the substrate. We further demonstrate that this anisotropy extends to dynamic behavior as well, with droplets sliding more quickly in parallel, rather than perpendicular, to the stretch direction. By demonstrating that stretched, stiffer substrates do not reveal asymmetric wetting, we conclude that surface stresses contribute to this particular contact behavior. Subsequently in this thesis, the dynamics of how contact is established between a rigid glass spherical indenter and a soft PDMS substrate are explored. Here we confirmed that contact radius and tensile force during the initiation of zero-indentation contact both grow monotonically with substrate stiffness and indenter size. We determined that the growth curves over time could be collapsed onto universal curves showing overall logarithmic growth for each parameter set. Furthermore by combining the force and contact radius measurements, we were able to see hints of a weak power law dependence between the two. The final portion of this dissertation delves into some unexpected behavior we observed while exploring contact initiation. We found that electrostatic forces can have a significant influence on the adhesion dynamics between a PDMS substrate and a glass sphere. As the substrate was approached by the force probe, we measured an, in part, power law growth of force with distance from the surface. More surprisingly, we found that our soft PDMS substrate was able to jump multiple microns into contact with the indenter. This jump led to the establishment of a lasting adhesive contact for the softest substrate. Slightly stiffer substrates exhibited repeated attachment and detachment cycles over hundreds of seconds, with little to no change in the tensile force at attachment over that time. To our knowledge, this is the first time electrostatic forces have been observed to influence the contact behavior of soft solids. The investigations in this dissertation provide new experimental insights into the contact mechanics of compliant solids. We establish the existence of some previously unknown behaviors in both static and dynamics wetting and adhesion, making a significant contribution towards our further understanding of the contact behavior of soft substrates. Our work also lays important groundwork for future research into the interesting phenomena encountered herein.
- Elastomers Fail from the EdgeNan Xue, Rong Long, Eric Dufresne and Robert StylePhysical Review X, vol. 14: no. 1, pp. 011054, American Physical Society, 2024.
The performance of soft devices is limited by the fracture resistance of elastomers. Thus, understanding how fracture resistance changes with material and sample geometry is an important challenge. A key observation is that thicker elastomers can be significantly tougher than thinner ones. We show that this surprising toughness enhancement in thick samples emerges from the 3D geometry of the fracture process. In contrast to the classical picture of a 2D crack, failure is driven by the growth of two separate "edge"cracks that nucleate early on at a sample's sides. As loading is increased, these cracks propagate in towards the sample midplane. When they merge, samples reach their ultimate failure strength. In thicker samples, edge cracks need to propagate farther before meeting, resulting in increased sample toughness. We demonstrate that edge-crack growth is controlled by the elastomer's strain-stiffening properties. Our results have direct implications for how to effectively toughen elastomers by controlling their geometry and large-strain mechanical properties.
- Elastic microphase separation produces robust bicontinuous materialsCarla Fernández Rico, Sanjay Schreiber, Hamza Oudich, Charlotta Lorenz, Alba Sicher, Tianqi Sai, Viola Bauernfeind, Stefanie Heyden, Pietro Carrara, Laura De Lorenzis, Robert Style and Eric DufresneNature Materials, vol. 23: no. 1, pp. 124-130, Nature, 2024.
Bicontinuous microstructures are essential to the function of diverse natural and synthetic systems. Their synthesis has been based on two approaches: arrested phase separation or self-assembly of block copolymers. The former is attractive for its chemical simplicity and the latter, for its thermodynamic robustness. Here we introduce elastic microphase separation (EMPS) as an alternative approach to make bicontinuous microstructures. Conceptually, EMPS balances the molecular-scale forces that drive demixing with large-scale elasticity to encode a thermodynamic length scale. This process features a continuous phase transition, reversible without hysteresis. Practically, EMPS is triggered by simply supersaturating an elastomeric matrix with a liquid, resulting in uniform bicontinuous materials with a well-defined microscopic length scale tuned by the matrix stiffness. The versatility of EMPS is further demonstrated by fabricating bicontinuous materials with superior mechanical properties and controlled anisotropy and microstructural gradients. Overall, EMPS presents a robust alternative for the bulk fabrication of homogeneous bicontinuous materials.
- Phase-separated droplets swim to their dissolutionEtienne Jambon-Puillet, Andrea Testa, Charlotta Lorenz, Robert Style, Aleksander Rebane and Eric DufresneNature Communications, vol. 15: no. 1, pp. 3919, Nature, 2024.
Biological macromolecules can condense into liquid domains. In cells, these condensates form membraneless organelles that can organize chemical reactions. However, little is known about the physical consequences of chemical activity in and around condensates. Working with model bovine serum albumin (BSA) condensates, we show that droplets swim along chemical gradients. Active BSA droplets loaded with urease swim toward each other. Passive BSA droplets show diverse responses to externally applied gradients of the enzyme’s substrate and products. In all these cases, droplets swim toward solvent conditions that favor their dissolution. We call this behavior “dialytaxis”, and expect it to be generic, as conditions which favor dissolution typically reduce interfacial tension, whose gradients are well-known to drive droplet motion through the Marangoni effect. These results could potentially suggest alternative physical mechanisms for active transport in living cells, and may enable the design of fluid micro-robots.
2023
- Polycrystallinity Enhances Stress Buildup around IceDominic Gerber, Lawrence A. Wilen, Eric Dufresne and Robert StylePhysical Review Letters, vol. 131: no. 20, pp. 208201, American Physical Society, 2023.
Damage caused by freezing wet, porous materials is a widespread problem but is hard to predict or control. Here, we show that polycrystallinity significantly speeds up the stress buildup process that underpins this damage. Unfrozen water in grain-boundary grooves feeds ice growth at temperatures below the freezing temperature, leading to fast stress buildup. These stresses can build up to levels that can easily break many brittle materials. The dynamics of the process are very variable, which we ascribe to local differences in ice-grain orientation and to the surprising mobility of many grooves-which further accelerates stress buildup. Our Letter will help understand how freezing damage occurs and in developing accurate models and effective damage-mitigation strategies.
- Surface Passivation Method for the Super-repellence of Aqueous Macromolecular CondensatesAndrea Testa, Hendrik T. Spanke, Etienne Jambon-Puillet, Mohammad Yasir, Yanxia Feng, Andreas M. Küffner, Paolo Arosio, Eric Dufresne, Robert Style and Aleksander RebaneLangmuir, vol. 39: no. 41, pp. 14626-14637, American Chemical Society, 2023.
Solutions of macromolecules can undergo liquid-liquid phase separation to form droplets with ultralow surface tension. Droplets with such low surface tension wet and spread over common surfaces such as test tubes and microscope slides, complicating in vitro experiments. The development of a universal super-repellent surface for macromolecular droplets has remained elusive because their ultralow surface tension requires low surface energies. Furthermore, the nonwetting of droplets containing proteins poses additional challenges because the surface must remain inert to a wide range of chemistries presented by the various amino acid side chains at the droplet surface. Here, we present a method to coat microscope slides with a thin transparent hydrogel that exhibits complete dewetting (contact angles θ ≈ 180°) and minimal pinning of phase-separated droplets in aqueous solution. The hydrogel is based on a swollen matrix of chemically cross-linked polyethylene glycol diacrylate of molecular weight 12 kDa (PEGDA), and can be prepared with basic chemistry laboratory equipment. The PEGDA hydrogel is a powerful tool for in vitro studies of weak interactions, dynamics, and the internal organization of phase-separated droplets in aqueous solutions.
- The generalized Clapeyron equation and its application to confined ice growthRobert Style, Dominic Gerber, Alan W. Rempel and Eric DufresneJournal of Glaciology, vol. 69: no. 276, pp. 1091-1096, Cambridge University Press, 2023.
Most theoretical descriptions of stresses induced by freezing are rooted in the (generalized) Clapeyron equation, which predicts the pressure that a solid can exert as it cools below its melting temperature. This equation is central for topics ranging beyond glaciology to geomorphology, civil engineering, food storage and cryopreservation. However, it has inherent limitations, requiring isotropic solid stresses and conditions near bulk equilibrium. Here, we examine when the Clapeyron equation is applicable by providing a rigorous derivation that details all assumptions. We demonstrate the natural extension for anisotropic stress states, and we show how the temperature and pressure ranges for validity depend on well-defined material properties. Finally, we demonstrate how the range of applicability of the (linear) Clapeyron equation can be extended by adding higher-order terms, yielding results that are in good agreement with experimental data for the pressure melting of ice.
- Strain stiffening elastomers with swelling inclusionsStefanie Heyden, Robert Style and Eric DufresneSoft Matter, vol. 19: no. 23, pp. 4385-4390, Royal Society of Chemistry, 2023.
Inhomogeneously swollen elastomers are an emergent class of materials, comprising elastic matrices with inclusion phases in the form of microgel particles or osmolytes. Inclusion phases can undergo osmotically driven swelling and deswelling over orders of magnitude. In the swollen state, the inclusions typically have negligible Young's modulus, and the matrix is strongly deformed. In that regime, the effective mechanical properties of the composite are governed by the matrix. Laying the groundwork for a generic analysis of inhomogeneously swollen elastomers, we develop a model based on incremental mean-field homogenization of a hyperelastic matrix. The framework allows for the computation of the macroscopic effective stiffness for arbitrary hyperelastic matrix materials. For an in-depth quantification of the local effective stiffness, we extend the concept of elastic stiffness maps to incompressible materials. For strain-stiffening materials, stiffness maps in the swollen state highlight pronounced radial stiffening with a non-monotonic change in stiffness in the hoop direction. Stiffening characteristics are sensitive to the form of constitutive models, which may be exploited in the design of hydrated actuators, soft composites and metamaterials. For validation, we apply this framework to a Yeoh material, and compare to recently published data. Model predictions agree well with experimental data on elastomers with highly swollen embedded microgel particles. We identify three distinct regimes related to an increasing degree of particle swelling: first, an initial decrease in composite stiffness is attributed to particle softening upon liquid intake. Second, dilute particle swelling leads to matrix stiffening dominating over particle softening, resulting in an increase in composite stiffness. Third, for swelling degrees beyond the dilute limit, particle interactions dominate further matrix stiffening.
- ATRP Enhances Structural Correlations In Polymerization-Induced Phase Separation**Alba Sicher, Richard Bradley Whitfield, Jan Ilavsky, Vinodkumar Saranathan, Athina Anastasaki and Eric DufresneAngewandte Chemie. International Edition, vol. 62: no. 16, pp. e202217683, Wiley-VCH, 2023.
Synthetic methods to control the structure of materials at sub-micron scales are typically based on the self-assembly of structural building blocks with precise size and morphology. On the other hand, many living systems can generate structure across a broad range of length scales in one step directly from macromolecules, using phase separation. Here, we introduce and control structure at the nano- and microscales through polymerization in the solid state, which has the unusual capability of both triggering and arresting phase separation. In particular, we show that atom transfer radical polymerization (ATRP) enables control of nucleation, growth, and stabilization of phase-separated poly-methylmethacrylate (PMMA) domains in a solid polystyrene (PS) matrix. ATRP yields durable nanostructures with low size dispersity and high degrees of structural correlations. Furthermore, we demonstrate that the length scale of these materials is controlled by the synthesis parameters.
- Effect of curvature on the diffusion of colloidal bananasJustin-Aurel Ulbrich, Carla Fernández Rico, Brian Rost, Jacopo Vialetto, Lucio Isa, Jeffrey S. Urbach and Roel P.A. DullensPhysical Review E, vol. 107: no. 4, pp. L042602, American Physical Society, 2023.
Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior. In this Letter, we investigate the two-dimensional diffusion of smoothly curved colloidal rods - also known as colloidal bananas - as a function of their opening angle α. We measure the translational and rotational diffusion coefficients of the particles with opening angles ranging from 0∘ (straight rods) to nearly 360∘(closed rings). In particular, we find that the anisotropic diffusion of the particles varies nonmonotonically with their opening angle and that the axis of fastest diffusion switches from the long to the short axis of the particles when α>180∘. We also find that the rotational diffusion coefficient of nearly closed rings is approximately an order of magnitude higher than that of straight rods of the same length. Finally, we show that the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles.
- Siloxane Molecules: Nonlinear Elastic Behavior and Fracture CharacteristicsTianchi Li, Eric Dufresne, Martin Kröger and Stefanie HeydenMacromolecules, vol. 56: no. 4, pp. 1303-1310, American Chemical Society, 2023.
Fracture phenomena in soft materials span multiple length and time scales. This poses a major challenge in computational modeling and predictive materials design. To pass quantitatively from molecular to continuum scales, a precise representation of the material response at the molecular level is vital. Here, we derive the nonlinear elastic response and fracture characteristics of individual siloxane molecules using molecular dynamics (MD) studies. For short chains, we find deviations from classical scalings for both the effective stiffness and mean chain rupture times. A simple model of a nonuniform chain of Kuhn segments captures the observed effect and agrees well with MD data. We find that the dominating fracture mechanism depends on the applied force scale in a nonmonotonic fashion. This analysis suggests that common polydimethylsiloxane (PDMS) networks fail at cross-linking points. Our results can be readily lumped into coarse-grained models. Although focusing on PDMS as a model system, our study presents a general procedure to pass beyond the window of accessible rupture times in MD studies employing mean first passage time theory, which can be exploited for arbitrary molecular systems.
- Understanding the pancake-like morphology of Golgi apparatus compartmentsGianna C. Wolfisberg, Hendrik T. Spanke, Alexandre Torzynski, Eric Dufresne and Aleksander A. RebaneBiophysical Journal, vol. 122: no. 3S1, pp. 220a, Cell Press, 2023.
- Stress Generation and Fracture in Freezing MaterialsDominic GerberDoctoral Thesis, Zurich, ETH Zurich, 2023.
- Polymerisation From Lipid MembranesAlexandre TorzynskiDoctoral Thesis, Zurich, ETH Zurich, 2023.
2022
- Cell-Derived Vesicles with Increased Stability and On-Demand Functionality by Equipping Their Membrane with a Cross-Linkable CopolymerXinan Huang, Dimitri Hürlimann, Hendrik Spanke, Dalin Wu, Michal Skowicki, Ionel Adrian Dinu, Eric Dufresne and Cornelia G. PalivanAdvanced Healthcare Materials, vol. 11: no. 23, pp. 2202100, Wiley-VCH, 2022.
Cell-derived vesicles retain the cytoplasm and much of the native cell membrane composition. Therefore, they are attractive for investigations of membrane biophysics, drug delivery systems, and complex molecular factories. However, their fragility and aggregation limit their applications. Here, the mechanical properties and stability of giant plasma membrane vesicles (GPMVs) are enhanced by decorating them with a specifically designed diblock copolymer, cholesteryl-poly[2-aminoethyl methacrylate-b-poly(ethylene glycol) methyl ether acrylate]. When cross-linked, this polymer brush enhances the stability of the GPMVs. Furthermore, the pH-responsiveness of the copolymer layer allows for a controlled cargo loading/release, which may enable various bioapplications. Importantly, the cross-linked-copolymer GPMVs are not cytotoxic and preserve in vitro membrane integrity and functionality. This effective strategy to equip the cell-derived vesicles with stimuli-responsive cross-linkable copolymers is expected to open a new route to the stabilization of natural membrane systems and overcome barriers to biomedical applications.
- Structural control in polymerization-induced phase separation in the solid-stateAlba SicherDoctoral Thesis, Zurich, ETH Zurich, 2022.
The micro- and nanostructure of materials determines their macroscopic properties. Currently, most synthetic methods used to control structure at these length scales consist of controlling the size and morphology of structural building blocks. Typically, these fabrication processes involves two distinct steps: the synthesis of the blocks, followed by their assembly. Instead, living systems generate structures across a broad range of length scales in one step directly from macromolecules, whose dimensions are much smaller than the characteristic scale of the final structure. Inspired by these examples, we wanted to learn how to introduce and control structure in materials at the nano- and microscale without having to pre-engineer the building blocks. Our strategies leveraged polymerization-induced phase separation in the solid state. First, we demonstrated how polymerization has the unique capability of triggering, controlling, and arresting phase separation. Afterwards, we described how we exploited this ability to make durable, structurally correlated nanocomposites. Finally, we explain how we tuned the process parameters to control the length scale of the obtained structure. In some cases, the synthesized materials were able to display structural color.
- Diatoms Knit together Biopolymers and SilicaMaria FeofilovaChimia, vol. 76: no. 9, pp. 795-795, Swiss Chemical Society, 2022.
- Hydroelastomers: soft, tough, highly swelling compositesSimon Moser, Yanxia Feng, Öncay Yasa, Stefanie Heyden, Michael Kessler, Esther Amstad, Eric Dufresne, Robert K. Katzschmann and Robert StyleSoft Matter, vol. 18: no. 37, pp. 7229-7235, Royal Society of Chemistry, 2022.
Inspired by the cellular design of plant tissue, we present an approach to make versatile, tough, highly water-swelling composites. We embed highly swelling hydrogel particles inside tough, water-permeable, elastomeric matrices. The resulting composites, which we call hydroelastomers, combine the properties of their parent phases. From their hydrogel component, the composites inherit the ability to highly swell in water. From the elastomeric component, the composites inherit excellent stretchability and fracture toughness, while showing little softening as they swell. Indeed, the fracture properties of the composite match those of the best-performing, tough hydrogels, exhibiting fracture energies of up to 10 kJ m(-2). Our composites are straightforward to fabricate, based on widely-available materials, and can easily be molded or extruded to form shapes with complex swelling geometries. Furthermore, there is a large design space available for making hydroelastomers, since one can use any hydrogel as the dispersed phase in the composite, including hydrogels with stimuli-responsiveness. These features make hydroelastomers excellent candidates for use in soft robotics and swelling-based actuation, or as shape-morphing materials, while also being useful as hydrogel replacements in other fields.
- Stress accumulation by confined ice in a temperature gradientDominic Gerber, Lawrence A. Wilen, Florian Poydenot, Eric Dufresne and Robert StyleProceedings of the National Academy of Sciences of the United States of America, vol. 119: no. 31, pp. e2200748119, National Academy of Sciences, 2022.
When materials freeze, they often undergo damage due to ice growth. Although this damage is commonly ascribed to the volumetric expansion of water upon freezing, it is usually driven by the flow of water toward growing ice crystals that feeds their growth. The freezing of this additional water can cause a large buildup of stress. Here, we demonstrate a technique for characterizing this stress buildup with unprecedented spatial resolution. We create a stable ice-water interface in a controlled temperature gradient and measure the deformation of the confining boundary. Analysis of the deformation field reveals stresses applied to the boundary with [Formula: see text](micrometers) spatial resolution. Globally, stresses increase steadily over time as liquid water is transported to more deeply undercooled regions. Locally, stresses increase until ice growth is stalled by the confining stresses. Importantly, we find a strong localization of stresses, which significantly increases the likelihood of damage caused by the presence of ice, even in apparently benign freezing situations. Ultimately, the limiting stress that the ice exerts is proportional to the local undercooling, in accordance with the Clapeyron equation, which describes the equilibrium between a stressed solid and its melt. Our results are closely connected to the condensation pressure during liquid-liquid phase separation and the crystallization pressure for growing crystals. Thus, they are highly relevant in fields ranging from cryopreservation and frost heave to food science, rock weathering, and art conservation.
- Geometrical frustration of phase-separated domains in Coscinodiscus diatom frustulesMaria Feofilova, Silvan Schüepp, Roman Schmid, Florian Hacker, Hendrik T. Spanke, Nicolas Bain, Katharine E. Jensen and Eric DufresneProceedings of the National Academy of Sciences of the United States of America, vol. 119: no. 31, pp. e2201014119, National Academy of Sciences, 2022.
Diatoms are single-celled organisms with a cell wall made of silica, called the frustule. Even though their elaborate patterns have fascinated scientists for years, little is known about the biological and physical mechanisms underlying their organization. In this work, we take a top-down approach and examine the micrometer-scale organization of diatoms from the Coscinodiscus family. We find two competing tendencies of organization, which appear to be controlled by distinct biological pathways. On one hand, micrometer-scale pores organize locally on a triangular lattice. On the other hand, lattice vectors tend to point globally toward a center of symmetry. This competition results in a frustrated triangular lattice, populated with geometrically necessary defects whose density increases near the center.
- Reply to the 'Comment on "Surface elastic constants of a soft solid''' by E. Gutman, Soft Matter, 2022, 18, DOI: 10.1039/D1SM01412ANicolas Bain, Stefanie Heyden, Qin Xu, Robert Style and Eric DufresneSoft Matter, vol. 18: no. 24, pp. 4641-4642, Royal Society of Chemistry, 2022.
In response to Gutman's comment, we clarify the derivation of the Shuttleworth equation. In addition, we discuss the findings of our original paper in light of recent theoretical and experimental work on surface elasticity in soft solids.
- Non-specific adhesive forces between filaments and membraneless organellesThomas J. Böddeker, Kathryn A. Rosowski, Doris Berchtold, Leonidas Emmanouilidis, Yaning Han, Frédéric H.-T. Allain, Robert W. Style, Lucas Pelkmans and Eric DufresneNature Physics, vol. 18: no. 5, pp. 571-578, Nature, 2022.
Many membraneless organelles are liquid-like domains that form inside the active, viscoelastic environment of living cells through phase separation. To investigate the potential coupling of phase separation with the cytoskeleton, we quantify the structural correlations of membraneless organelles (stress granules) and cytoskeletal filaments (microtubules) in a human-derived epithelial cell line. We find that microtubule networks are substantially denser in the vicinity of stress granules. When microtubules are depolymerized, the sub-units localize near the surface of the stress granules. We interpret these data using a thermodynamic model of partitioning of particles to the surface and bulk of the droplets. In this framework, our data are consistent with a weak (≲kBT) affinity of the microtubule sub-units for stress granule interfaces. As microtubules polymerize, their interfacial affinity increases, providing sufficient adhesion to deform droplets and/or the network. Our work suggests that proteins and other objects in the cell have a non-specific affinity for droplet interfaces that increases with the contact area and becomes most apparent when they have no preference for the interior of a droplet over the rest of the cytoplasm. We validate this basic physical phenomenon in vitro through the interaction of a simple protein–RNA condensate with microtubules.
- A robust method for quantification of surface elasticity in soft solidsStefanie Heyden, Petia M. Vlahovska and Eric DufresneJournal of the Mechanics and Physics of Solids, vol. 161, pp. 104786, Elsevier, 2022.
We propose an approach to measure surface elastic constants of soft solids. Generally, this requires one to probe interfacial mechanics at around the elastocapillary length scale, which is typically microscopic. Deformations of microscopic droplets embedded in soft solids are particularly attractive, because they avoid intrinsic nonlinearities associated with previous experiments such as the equilibrium of contact lines and the relaxation of patterned surfaces. We derive analytical solutions for the shape of droplets under uniaxial deformation and for the radius of droplets upon hydrostatic inflation. We couple mechanical deformations to the dissolution of droplets to assess experimental sensitivities. Combined with experimental data from both modes of deformation, one should be able to reliably extract the complete set of isotropic surface material parameters following a specific minimization procedure.
- Gradients in solid surface tension drive Marangoni-like motions in cell aggregatesVikrant Yadav, Md. Sulaiman Yousafzai, Sorosh Amiri, Robert W. Style, Eric Dufresne and Michael MurrellPhysical Review Fluids, vol. 7: no. 3, pp. L031101, American Physical Society, 2022.
The surface tension of living cells and tissues originates from the generation of nonequilibrium active stresses within the cell cytoskeleton. Here, using laser ablation, we generate gradients in the surface tension of cellular aggregates as models of simple tissues. These gradients of active surface stress drive large-scale and rapid toroidal motion. Subsequently, the motions spontaneously reverse as stresses reaccumulate and cells return to their original positions. Both forward and reverse motions resemble Marangoni flows in viscous fluids. However, the motions are faster than the timescales of viscoelastic relaxation and the surface tension gradient is proportional to mechanical strain at the surface. Further, due to active stress, both the surface tension gradient and surface strain are dependent upon the volume of the aggregate. These results indicate that surface tension can induce rapid and highly correlated elastic deformations in the maintenance of tissue shape and configuration.
- Fracture of hierarchical multi-layered bioinspired compositesTommaso Magrini, Ayca Senol Güngör, Robert Style, Florian Bouville and André R. StudartJournal of the Mechanics and Physics of Solids, vol. 159, pp. 104750, Elsevier, 2022.
Lightweight composites have revolutionized the sector of aircrafts and will continue to play a major role in future energy-efficient transportation systems. However, the design of composites featuring high strength and high fracture toughness remains challenging due to the usual trade-off between these properties in synthetic materials. Inspired by the strong and tough hierarchical architecture of mollusk shells, we create tough composites by combining soft polymer layers with alternating, nacre-like layers that are infiltrated with the same polymer. Here, we study the fracture behavior and the toughening mechanisms underlying the high crack growth resistance of these hierarchical composites. Polymer layers with different stiffness and yield strength were designed in order to evaluate the effect of plastic deformation and bridging of the polymer phase on the early and late stages of the fracture process. Controlled fracture experiments allowed us to visualize the interactions of a propagating crack with the hierarchical architecture and to quantify the resistance of the polymer layer against early-stage fracture. Our findings provide new insights into the interplay of multiscale toughening mechanisms in hierarchical bioinspired architectures and offer guidelines for the design and manufacturing of strong and tough lightweight composites.
- Putting the Squeeze on Phase SeparationCarla Fernández Rico, Tianqi Sai, Alba Sicher, Robert Style and Eric DufresneJACS Au, vol. 2: no. 1, pp. 66-73, American Chemical Society, 2022.
Phase separation is a ubiquitous process and finds applications in a variety of biological, organic, and inorganic systems. Nature has evolved the ability to control phase separation to both regulate cellular processes and make composite materials with outstanding mechanical and optical properties. Striking examples of the latter are the vibrant blue and green feathers of many bird species, which are thought to result from an exquisite control of the size and spatial correlations of their phase-separated microstructures. By contrast, it is much harder for material scientists to arrest and control phase separation in synthetic materials with such a high level of precision at these length scales. In this Perspective, we briefly review some established methods to control liquid-liquid phase separation processes and then highlight the emergence of a promising arrest method based on phase separation in an elastic polymer network. Finally, we discuss upcoming challenges and opportunities for fabricating microstructured materials via mechanically controlled phase separation.
- Absorption- Enhanced Scattering for Structural ColorTianqi SaiDoctoral Thesis, Zurich, ETH Zurich, 2022.
- Dynamics of spontaneous wrapping of microparticles by floppy lipid membranesHendrik Spanke, Jaime Agudo-Canalejo, Daniel Tran, Robert Style and Eric DufresnePhysical Review Research, vol. 4: no. 2, pp. 023080, American Physical Society, 2022.
Lipid membranes form the barrier between the inside and outside of cells and many of their subcompartments. As such, they bind to a wide variety of nano- and micrometer sized objects and, in the presence of strong adhesive forces, strongly deform and envelop particles. This wrapping plays a key role in many healthy and disease-related processes. So far, little work has focused on the dynamics of wrapping. Here, using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure the velocity of the particle during wrapping as well as the forces exerted on it by the lipid membrane. Dissipation near the contact line appears to be the main factor determining the wrapping velocity and time to wrap an object.
- Biomimetic Active Protein DropletsAndrea TestaDoctoral Thesis, Zurich, ETH Zurich, 2022.
Living cells are continuously driven out of equilibrium by the intricate interplay of the many chemical processes that we call life. They are able to sustain these processes by harvesting energy from their environment through metabolism, which extracts potential energy from a chemical fuel. These reactions happen in a cellular environment that is a crowded, complex and highly dynamic mixture of concentrated macromolecules, oligomers and small molecules. For this reasons, describing and understanding biological phenomena is extremely challenging, and in vitro experiments are typically performed in very dilute, close-to-equilibrium conditions, which fail to capture the essential features ofthe cellular medium. In this thesis, we introduce a minimal system that operates at similar metabolic densities, protein concentrations and length scales as living cells, while still being simple enough to understand and control. Inspired by membraneless organelles, we exploit the liquid-liquid phase separation of bovine serum albumin in presence of a polymer to create highly crowded protein domains, which spontaneously partition enzymes. By dispersing the droplets in a reservoir ofsubstrate-loaded buffer, we are able to obtain local metabolic densities that match those of the hungriest living organisms. The membraneless nature ofthese microreactors allows efficient exchange of chemicals and heat, and in turn the possibility to achieve steady states. We further demonstrate that metabolic activity is capable of promoting a plethora ofbiomimetic behaviors, like the formation of pH gradients, microscopic flows, and droplet motion. Our work provides a flexible platform for the study of biological phenomena in an environment that mimics the cellular cytoplasm, and more in general for the understanding of systems driven far from equilibrium and their emergent collective behavior. It also establishes a framework and a set of design rules for working with active droplet systems, including the development of a novel slippery glass coating that exhibits zero-wetting conditions for a wide range ofmacromolecular condensates and lipid vesicles.
- Wrapping of Microparticles by Lipid MembranesHendrik T. SpankeDoctoral Thesis, Zurich, ETH Zurich, 2022.
Lipid membranes play an essential role in both the morphology and functionality of living cells. They not only delineate the inside and outside of all eukaryotic cells but also define a number of organelles inside these cells. Cells come into contact with many different objects like particles, pathogens or smaller compartments confined by a lipid membrane, such as vesicles. It is thus essential to understand how membranes interact with such objects and how this interaction is impacted by the physical properties of the membranes. In this thesis, a novel model system to study particle-membrane interactions in proposed. This model system consists of micron-sized particles and giant unilamellar vesicles (GUVs) that interact via nonspecific depletion interactions. In the first part of this thesis, we address the specific conditions for the wrapping of single particles by the membrane. We found three distinct regimes of wrapping: While at low particle-membrane adhesion energies, the membrane does not wrap around the particle, at high adhesion energies particles are spontaneously wrapped. At intermediate adhesion energies particles are wrapped only when an external force is applied. This regime is stabilized by membrane curvature. In the second part of this thesis the dynamics of particle wrapping is investigated in the spontaneous wrapping regime at high adhesion energies. The wrapping dynamics are found to be largely independent of the particle size. Dissipation at the contact line appears to be the dominant process determining the wrapping velocity. However, we observe discrepancies in the experimentally observed wrapping velocities when compared to expected wrapping velocities in a quasistatic model of the system. These discrepancies suggest another process at play on top of dissipation at the contact line. A possible explanation of this phenomena is that the membrane is deformed on a size and timescale in these experiments that the membrane shear viscosity comes into play. The findings of this thesis provide new experimental insights into particle-membrane interactions. Particularly, the proposed novel model system allows for a large number of new experiments offering deeper understanding of membrane mechanics, how cells interact with their environment and how cells shape themselves.
- The effect of surface-active statistical copolymers in low-energy miniemulsion and RAFT polymerizationManon Rolland, Eric Dufresne, Nghia Truong Phuoc and Athina AnastasakiPolymer Chemistry, vol. 2022: no. 13, pp. 5135-5144, Royal Society of Chemistry, 2022.
Low-energy miniemulsions enable the production of uniform nanodroplets for a wide range of applications without the need for using specialized equipment. However, low-energy miniemulsions are typically formed in the presence of a surface-active agent with a specific structure and property. In this work, we elucidate the role of a surface-active statistical copolymer, poly(N-(2-hydroxypropyl) methacrylamide-co-di(ethylene glycol) ethyl ether methacrylate) P(HPMA-co-DEGMA), in the formation of low-energy miniemulsions and reversible addition-fragmentation chain-transfer (RAFT) polymerization, enabling the design of a new series of surface-active statistical copolymers. In particular, we found that the HPMA/DEGMA ratio and copolymer molecular weight significantly affect the interfacial tension between water and styrene and as a result, the size of nanodroplets and the RAFT miniemulsion polymerization. Importantly, these findings allowed for the design and synthesis of novel surface-active statistical copolymers composed of DEGMA and various hydrophilic moieties that can also substantially lower the interfacial tension to below 12 mN m(-1). Furthermore, the new copolymer of DEGMA with methacrylamide (MAAm) resulted in the smallest nanodroplet size. This copolymer was subsequently selected to trigger the RAFT polymerization of styrene yielding nanoparticles of different morphologies including worm balls, worms, and vesicles. This work sheds light on the role of surface-active statistical copolymers and significantly expands the availability of surface-active agents for low-energy miniemulsion and RAFT polymerization.
- Physical interactions of membraneless organelles with the cytoskeletonThomas Josef BöddekerDoctoral Thesis, Zurich, ETH Zurich, 2022.
Cells are the basic building blocks of life. As such, they perform a plethora of functions, often realized through organelles, functional sub-units in the cell. Organelles have classically been though of as membrane-enclosed compartments. Recent advances, however, have shown that there are many organelles that lack a defining lipid membrane. Many such membraneless organelles, typically composed of protein and RNA, are liquid-like domains that form through phase separation inside the active, viscoelastic environment of living cells. While the ability of membraneless organelles to concentrate and segregate proteins within their bulk has been widely recognized, the importance of their surface is just starting to be appreciated. The surface energy of liquid interfaces leads to capillary phenomena, such as adhesion and wetting. The liquid-like nature of membraneless organelles thus suggests rich interactions between such droplets and other structures in the cell. In this thesis, we developed new statistical tools and physical theory to explore such phenomena and apply them to the interactions of stress granules, a membraneless organelle, with the components of the cytoskeleton. Microscopy is an important experimental tool to study living cells. However, due to the extremely complex and fluctuating environment in the cell, it is difficult to extract meaningful information on interactions between intracellular structures from individual images. Furthermore, images from different cells are often not comparable. We introduce a novel image analysis method that overcomes these challenges through creation of meaningful averages and reference states across many cells. Using these newly developed tools, we find that the microtubule network, which is an essential component of the cytoskeleton, is substantially denser in the vicinity of stress granules. When microtubules are depolymerized, their molecular building blocks adhere to the surface of stress granules. We capture this experimental observation in a thermodynamic model of partitioning of particles to the interface and bulk of two liquid phases. In this framework, our data are consistent with a weak (below kT) affinity of the microtubule sub-units for stress granule interfaces. As microtubules polymerize, their interfacial affinity increases, providing sufficient adhesion to deform droplets and/or the microtubule network. We validate this basic physical phenomenon in vitro through the interaction of a simple protein–RNA condensate with microtubules and their building blocks. Our work suggests that proteins and other objects in the cell have a non-specific affinity for droplet interfaces that increases with the contact area and becomes most apparent when they have no preference for the interior of a droplet over the rest of the cytoplasm. Another essential component of the cytoskeleton is actin, which forms dynamic networks that exhibit constant turnover and flow, which is important for cell motility. Similar analyses as for microtubules reveal repulsive interactions between stress granules and actin. Additionally, we find that stress granule motion is correlated with the flow of the actin network and that hydrodynamic coupling of stress granules and actin leads to directed transport towards microtubule-rich regions of the cell. Combined, our results present a comprehensive view of the interactions of stress granules with filamentous actin and microtubules. Stress granules are affected by wetting-mediated interactions with microtubules as well as hydrodynamic coupling to actin flow. Both of these physical mechanisms are non-specific, and therefore should be broadly applicable to other membraneless organelles and structures in the cell.
2021
- Pathway-Dependent Grain Coarsening of Block Copolymer Patterns under Controlled Solvent EvaporationArkadiusz A. Leniart, Przemyslaw Pula, Robert W. Style and Pawel W. MajewskiACS Macro Letters, vol. 11, pp. 121-126, American Chemical Society, 2021.
Solvent evaporation annealing (SEA) is a straightforward, single-step casting and annealing method of block copolymers (BCP) processing yielding large-grained morphologies in a very short time. Here, we present a quantitative analysis of BCP grain-coarsening in thin films under controlled evaporation of the solvent. Our study is aimed at understanding time and BCP concentration influence on the rate of the lateral growth of BCP grains. By systematically investigating the coarsening kinetics at various BCP concentrations, we observed a steeply decreasing exponential dependence of the kinetics power-law time exponent on polymer concentration. We used this dependence to formulate a mathematical model of BCP ordering under nonstationary conditions and a 2D, time- and concentration-dependent coarsening rate diagram, which can be used as an aid in engineering the BCP processing pathway in SEA and also in other directed self-assembly methods that utilize BCP-solvent interactions such as solvent vapor annealing.
- Shape-Controlled Nanoparticles from a Low-Energy NanoemulsionManon Rolland, Nghia Truong Phuoc, Kostas Parkatzidis, Emily H. Pilkington, Alexandre Torzynski, Robert Style, Eric Dufresne and Athina AnastasakiJACS Au, vol. 1: no. 11, pp. 1975-1986, American Chemical Society, 2021.
Nanoemulsion technology enables the production of uniform nanoparticles for a wide range of applications. However, existing nanoemulsion strategies are limited to the production of spherical nanoparticles. Here, we describe a low-energy nanoemulsion method to produce nanoparticles with various morphologies. By selecting a macro-RAFT agent (poly(di(ethylene glycol) ethyl ether methacrylate-co-N-(2-hydroxypropyl) methacrylamide) (P(DEGMA-co-HPMA))) that dramatically lowers the interfacial tension between monomer droplets and water, we can easily produce nanoemulsions at room temperature by manual shaking for a few seconds. With the addition of a common ionic surfactant (SDS), these nanoscale droplets are robustly stabilized at both the formation and elevated temperatures. Upon polymerization, we produce well-defined block copolymers forming nanoparticles with a wide range of controlled morphologies, including spheres, worm balls, worms, and vesicles. Our nanoemulsion polymerization is robust and well-controlled even without stirring or external deoxygenation. This method significantly expands the toolbox and availability of nanoemulsions and their tailor-made polymeric nanomaterials.
- Surface Tension and the Strain-Dependent Topography of Soft SolidsNicolas Bain, Anand Jagota, Katrina Smith-Mannschott, Stefanie Heyden, Robert Style and Eric DufresnePhysical Review Letters, vol. 127: no. 20, pp. 208001, American Physical Society, 2021.
When stretched in one direction, most solids shrink in the transverse directions. In soft silicone gels, however, we observe that small-scale topographical features grow upon stretching. A quantitative analysis of the topography shows that this counterintuitive response is nearly linear, allowing us to tackle it through a small-strain analysis. We find that the surprising increase of small-scale topography with stretch is due to a delicate interplay of the bulk and surface responses to strain. Specifically, we find that surface tension changes as the material is deformed. This response is expected on general grounds for solid materials, but challenges the standard description of gel and elastomer surfaces.
- Enhancing the Refractive Index of Polymers with a Plant-Based PigmentMohammad Yasir, Tianqi Sai, Alba Sicher, Frank Scheffold, Ullrich Steiner, Bodo D. Wilts and Eric DufresneSmall, vol. 17: no. 44, pp. 2103061, Wiley, 2021.
Polymers are essential components of many nanostructured materials. However, the refractive indices of common polymers fall in a relatively narrow range between 1.4 and 1.6. Here, it is demonstrated that loading commercially-available polymers with large concentrations of a plant-based pigment can effectively enhance their refractive index. For polystyrene (PS) loaded with 67 w/w% beta-carotene (BC), a peak value of 2.2 near the absorption edge at 531 nm is achieved, while maintaining values above 1.75 across longer wavelengths of the visible spectrum. Despite high pigment loadings, this blend maintains the thermoforming ability of PS, and BC remains molecularly dispersed. Similar results are demonstrated for the plant-derived polymer ethyl cellulose (EC). Since the refractive index enhancement is intimately connected to the introduction of strong absorption, it is best suited to applications where light travels short distances through the material, such as reflectors and nanophotonic systems. Enhanced reflectance from films is experimentally demonstrated, as large as sevenfold for EC at selected wavelengths. Theoretical calculations highlight that this simple strategy can significantly increase light scattering by nanoparticles and enhance the performance of Bragg reflectors.
- Sustained enzymatic activity and flow in crowded protein dropletsAndrea Testa, Mirco Dindo, Aleksander Rebane, Babak Nasouri, Robert Style, Ramin Golestanian, Eric Dufresne and Paola LaurinoNature Communications, vol. 12: no. 1, pp. 6293, Nature, 2021.
Living cells harvest energy from their environments to drive the chemical processes that enable life. We introduce a minimal system that operates at similar protein concentrations, metabolic densities, and length scales as living cells. This approach takes advantage of the tendency of phase-separated protein droplets to strongly partition enzymes, while presenting minimal barriers to transport of small molecules across their interface. By dispersing these microreactors in a reservoir of substrate-loaded buffer, we achieve steady states at metabolic densities that match those of the hungriest microorganisms. We further demonstrate the formation of steady pH gradients, capable of driving microscopic flows. Our approach enables the investigation of the function of diverse enzymes in environments that mimic cytoplasm, and provides a flexible platform for studying the collective behavior of matter driven far from equilibrium.
- Micromirror Total Internal Reflection Microscopy for High-Performance Single Particle Tracking at InterfacesXuanhui Meng, Adar Sonn-Segev, Anne Schumacher, Daniel Cole, Gavin Young, Stephen Thorpe, Robert W. Style, Eric Dufresne and Philipp KukuraACS Photonics, vol. 8: no. 10, pp. 3111-3118, American Chemical Society, 2021.
Single particle tracking has found broad applications in the life and physical sciences, enabling the observation and characterization of nano- and microscopic motion. Fluorescence-based approaches are ideally suited for high-background environments, such as tracking lipids or proteins in or on cells, due to superior background rejection. Scattering-based detection is preferable when localization precision and imaging speed are paramount due to the in principle infinite photon budget. Here, we show that micromirror-based total internal reflection dark field microscopy enables background suppression previously only reported for interferometric scattering microscopy, resulting in nanometer localization precision at 6 μs exposure time for 20 nm gold nanoparticles with a 25 × 25 μm2 field of view. We demonstrate the capabilities of our implementation by characterizing sub-nanometer deterministic flows of 20 nm gold nanoparticles at liquid–liquid interfaces. Our results approach the optimal combination of background suppression, localization precision, and temporal resolution achievable with pure scattering-based imaging and tracking of nanoparticles at interfaces.
- Structural color from solid-state polymerization-induced phase separationAlba Sicher, Rabea Ganz, Andreas Menzel, Daniel Messmer, Guido Panzarasa, Maria Feofilova, Richard O. Prum, Robert W. Style, Vinodkumar Saranathan, René M. Rossi and Eric DufresneSoft Matter, vol. 17: no. 23, pp. 5772-5779, Royal Society of Chemistry, 2021.
Structural colors are produced by wavelength-dependent scattering of light from nanostructures. While living organisms often exploit phase separation to directly assemble structurally colored materials from macromolecules, synthetic structural colors are typically produced in a two-step process involving the sequential synthesis and assembly of building blocks. Phase separation is attractive for its simplicity, but applications are limited due to a lack of robust methods for its control. A central challenge is to arrest phase separation at the desired length scale. Here, we show that solid-state polymerization-induced phase separation can produce stable structures at optical length scales. In this process, a polymeric solid is swollen and softened with a second monomer. During its polymerization, the two polymers become immiscible and phase separate. As free monomer is depleted, the host matrix resolidifies and arrests coarsening. The resulting polymeric composites have a blue or white appearance. We compare these biomimetic nanostructures to those in structurally-colored feather barbs, and demonstrate the flexibility of this approach by producing structural color in filaments and large sheets.
- Evolution of single gyroid photonic crystals in bird feathersVinodkumar Saranathan, Suresh Narayanan, Alec Sandy, Eric Dufresne and Richard O. PrumProceedings of the National Academy of Sciences of the United States of America, vol. 118: no. 23, pp. e2101357118, National Academy of Sciences, 2021.
Vivid, saturated structural colors are conspicuous and important features of many animals. A rich diversity of three-dimensional periodic photonic nanostructures is found in the chitinaceous exoskeletons of invertebrates. Three-dimensional photonic nanostructures have been described in bird feathers, but they are typically quasi-ordered. Here, we report bicontinuous single gyroid β-keratin and air photonic crystal networks in the feather barbs of blue-winged leafbirds (Chloropsis cochinchinensis sensu lato), which have evolved from ancestral quasi-ordered channel-type nanostructures. Self-assembled avian photonic crystals may serve as inspiration for multifunctional applications, as they suggest efficient, alternative routes to single gyroid synthesis at optical length scales, which has been experimentally elusive.
- Dynamics and healing behavior of metallosupramolecular polymersLaura N. Neumann, Emad Oveisi, Albrecht Petzold, Robert W. Style, Thomas Thurn-Albrecht, Christoph Weder and Stephen SchrettlScience Advances, vol. 7: no. 18, pp. eabe4154, AAAS, 2021.
Self-healing or healable polymers can recuperate their function after physical damage. This process involves diffusion of macromolecules across severed interfaces until the structure of the interphase matches that of the pristine material. However, monitoring this nanoscale process and relating it to the mechanical recovery remain elusive. We report that studying diffusion across healed interfaces and a correlation of contact time, diffusion depth, and mechanical properties is possible when two metallosupramolecular polymers assembled with different lanthanoid salts are mended. The materials used display similar properties, while the metal ions can be tracked with high spatial resolution by energy-dispersive x-ray spectrum imaging. We find that healing actual defects requires an interphase thickness in excess of 100 nm, 10 times more than previously established for self-adhesion of smooth films of glassy polymers.
- Droplets Sit and Slide Anisotropically on Soft, Stretched SubstratesKatrina Smith-Mannschott, Qin Xu, Stefanie Heyden, Nicolas Bain, Jacco H. Snoeijer, Eric Dufresne and Robert W. StylePhysical Review Letters, vol. 126: no. 15, pp. 158004, American Physical Society, 2021.
Anisotropically wetting substrates enable useful control of droplet behavior across a range of applications. Usually, these involve chemically or physically patterning the substrate surface, or applying gradients in properties like temperature or electrical field. Here, we show that a flat, stretched, uniform soft substrate also exhibits asymmetric wetting, both in terms of how droplets slide and in their static shape. Droplet dynamics are strongly affected by stretch: Glycerol droplets on silicone substrates with a 23% stretch slide 67% faster in the direction parallel to the applied stretch than in the perpendicular direction. Contrary to classical wetting theory, static droplets in equilibrium appear elongated, oriented parallel to the stretch direction. Both effects arise from droplet-induced deformations of the substrate near the contact line.
- Forming Anisotropic Crystal Composites: Assessing the Mechanical Translation of Gel Network Anisotropy to Calcite Crystal FormDamian Palin, Robert W. Style, Jure Zlopaša, Jonathan J. Petrozzini, Mark A. Pfeifer, Henk M. Jonkers, Eric Dufresne and Lara A. EstroffJournal of the American Chemical Society, vol. 143: no. 9, pp. 3439-3447, American Chemical Society, 2021.
The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.
- Supramolecular gelation controlled by an iodine clockSolenn Riedel, Thomas Schweizer, Katrina Smith-Mannschott, Eric Dufresne and Guido PanzarasaSoft Matter, vol. 17: no. 5, pp. 1189-1193, Royal Society of Chemistry, 2021.
Programming supramolecular assembly in the time domain is a fundamental aspect of the design of biomimetic materials. We achieved the time-controlled sol–gel transition of a poly(vinyl alcohol)–iodine supramolecular complex by generating iodine in situ with a clock reaction. We demonstrate that both the gelation time and the mechanical properties of the resulting hydrogel can be tuned by properly selecting the clock parameters or through competitive iodine complexation.
- Surface tensiometry of phase separated protein and polymer droplets by the sessile drop methodMahdiye Ijavi, Robert W. Style, Leonidas Emmanouilidis, Sandro Meier, Alexandre Torzynski, Frédéric H.-T. Allain, Yves Barral, Michel O. Steinmetz and Eric DufresneSoft Matter, vol. 17: no. 6, pp. 1655-1662, Royal Society of Chemistry, 2021.
Phase separated macromolecules play essential roles in many biological and synthetic systems. Physical characterization of these systems can be challenging because of limited sample volumes, particularly for phase-separated proteins. Here, we demonstrate that a classic method for measuring the surface tension of liquid droplets, based on the analysis of the shape of a sessile droplet, can be effectively scaled down to measure the interfacial tension between a macromolecule-rich droplet phase and its co-existing macromolecule-poor continuous phase. The connection between droplet shape and surface tension relies on the density difference between the droplet and its surroundings. This can be determined with small sample volumes in the same setup by measuring the droplet sedimentation velocity. An interactive MATLAB script for extracting the capillary length from a droplet image is included in the ESI.
- Solid–Liquid Composites for Soft Multifunctional MaterialsRobert W. Style, Ravi Tutika, Jin Y. Kim and Michael D. BartlettAdvanced Functional Materials, vol. 31: no. 1, pp. 2005804, Wiley-VCH, 2021.
Soft materials with a liquid component are an emerging paradigm in materials design. The incorporation of a liquid phase, such as water, liquid metals, or complex fluids, into solid materials imparts unique properties and characteristics that emerge as a result of the dramatically different properties of the liquid and solid. Especially in recent years, this has led to the development and study of a range of novel materials with new functional responses, with applications in topics including soft electronics, soft robotics, 3D printing, wet granular systems and even in cell biology. Here a review of solid–liquid composites, broadly defined as a material system with at least one, phase-separated liquid component, is provided and discussed their morphology and fabrication approaches, their emergent mechanical properties and functional response, and the broad range of their applications. © 2020 Wiley-VCH GmbH
- Measuring Surface Tensions of Soft Solids with Huge Contact-Angle HysteresisJin Y. Kim, Stefanie Heyden, Dominic Gerber, Nicolas Bain, Eric Dufresne and Robert W. StylePhysical Review X, vol. 11: no. 3, pp. 031004, American Physical Society, 2021.
The equilibrium contact angle of a droplet resting on a solid substrate can reveal essential properties of the solid's surface. However, when the motion of a droplet on a surface shows significant hysteresis, it is generally accepted that the solid's equilibrium properties cannot be determined. Here, we describe a method to measure surface tensions of soft solids with strong wetting hysteresis. With independent knowledge of the surface tension of the wetting fluid and the linear-elastic response of the solid, the solid deformations under the contact line and the contact angle of a single droplet together reveal the difference in surface tension of the solid against the liquid and vapor phases If the solid's elastic properties are unknown, then this surface tension difference can be determined from the change in substrate deformations with contact angle. These results reveal an alternate equilibrium contact angle, equivalent to the classic form of Young-Dupre, but with surface tensions in place of surface energies. We motivate and apply this approach with experiments on gelatin, a common hydrogel.
- Contact lines on stretched soft solids: modelling anisotropic surface stressesStefanie Heyden, Nicolas Bain, Qin Xu, Robert W. Style and Eric DufresneProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 477: no. 2245, pp. 20200673, Royal Society, 2021.
We present fully analytical solutions for the deformation of a stretched soft substrate due to the static wetting of a large liquid droplet, and compare our solutions to recently published experiments (Xu et al. 2018 Soft Matter 14, 916–920 (doi:10.1039/C7SM02431B)). Following a Green’s function approach, we extend the surface-stress regularized Flamant–Cerruti problem to account for uniaxial pre-strains of the substrate. Surface profiles, including the heights and opening angles of wetting ridges, are provided for linearized and finite kinematics. We fit experimental wetting ridge shapes as a function of applied strain using two free parameters, the surface Lamé coefficients. In comparison with experiments, we find that observed opening angles are more accurately captured using finite kinematics, especially with increasing levels of applied pre-strain. These fits qualitatively agree with the results of Xu et al., but revise values of the surface elastic constants.
- Physical Characterization of Phase Separated Biomolecular CondensatesMahdiye IjaviDoctoral Thesis, Zurich, ETH Zurich, 2021.
2020
- Viscoelastic and Poroelastic Relaxations of Soft Solid SurfacesQin Xu, Lawrence A. Wilen, Katharine E. Jensen, Robert W. Style and Eric DufresnePhysical Review Letters, vol. 125: no. 23, pp. 238002, American Physical Society, 2020.
Understanding surface mechanics of soft solids, such as soft polymeric gels, is crucial in many engineering processes, such as dynamic wetting and adhesive failure. In these situations, a combination of capillary and elastic forces drives the motion, which is balanced by dissipative mechanisms to determine the rate. While shear rheology (i.e., viscoelasticity) has long been assumed to dominate the dissipation, recent works have suggested that compressibility effects (i.e., poroelasticity) could play roles in swollen networks. We use fast interferometric imaging to quantify the relaxation of surface deformations due to a displaced contact line. By systematically measuring the profiles at different time and length scales, we experimentally observe a crossover from viscoelastic to poroelastic surface relaxations. © 2020 American Physical Society.
- How surface stress transforms surface profiles and adhesion of rough elastic bodiesChung-Yuen Hui, Zezhou Liu, Nicolas Bain, Anand Jagota, Eric Dufresne, Robert W. Style, Ryuji Kiyama and Jian Ping GongProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 476: no. 2243, pp. 20200477, Royal Society, 2020.
The surface of soft solids carries a surface stress that tends to flatten surface profiles. For example, surface features on a soft solid, fabricated by moulding against a stiff-patterned substrate, tend to flatten upon removal from the mould. In this work, we derive a transfer function in an explicit form that, given any initial surface profile, shows how to compute the shape of the corresponding flattened profile. We provide analytical results for several applications including flattening of one-dimensional and two-dimensional periodic structures, qualitative changes to the surface roughness spectrum, and how that strongly influences adhesion.
- Wrapping of Microparticles by Floppy Lipid VesiclesHendrik Spanke, Robert W. Style, Claire Francois-Martin, Maria Feofilova, Manuel Eisentraut, Holger Kress, Jaime Agudo-Canalejo and Eric DufresnePhysical Review Letters, vol. 125: no. 19, pp. 198102, American Physical Society, 2020.
Lipid membranes, the barrier defining living cells and many of their subcompartments, bind to a wide variety of nano- and micrometer sized objects. In the presence of strong adhesive forces, membranes can strongly deform and wrap the particles, an essential step in crossing the membrane for a variety of healthy and disease-related processes. A large body of theoretical and numerical work has focused on identifying the physical properties that underly wrapping. Using a model system of micron-sized colloidal particles and giant unilamellar lipid vesicles with tunable adhesive forces, we measure a wrapping phase diagram and make quantitative comparisons to theoretical models. Our data are consistent with a model of membrane-particle interactions accounting for the adhesive energy per unit area, membrane bending rigidity, particle size, and vesicle radius. © 2020 American Physical Society.
- Two‐Stage Polyelectrolyte Assembly Orchestrated by a Clock ReactionChristian C.M. Sproncken, Berta Gumí‐Audenis, Guido Panzarasa and Ilja K. VoetsChemSystemsChem, vol. 2: no. 6, pp. e2000005, Wiley-VCH, 2020.
Controlling the transient self‐assembly of (macro)molecular building blocks is of fundamental interest, both to understand the dynamic processes occurring in living systems and to develop new generations of functional materials. The subtle interplay between different types of physicochemical interactions, as well as the possible reaction pathways, are crucial when both thermodynamic and kinetic factors play substantial roles, as in the case of transient supramolecular assemblies. Clock reactions are a promising tool to achieve temporal control over self‐assembly in non‐living materials. Here, we report on the tunable association of poly(allylamine hydrochloride) (PAH) fueled by the formaldehyde‐sulfite clock reaction. The electrostatic interaction between the large macromolecules and the small, oppositely charged sulfite ions gives rise to micron‐sized coacervate‐like complexes. As the clock proceeds, sulfite is completely depleted and the complexes dissociate. However, under suitable conditions, a subsequent reaction between the polyelectrolyte and formaldehyde can lock‐in the preformed supramolecular structure, giving rise to covalently crosslinked colloidal particles.
- Designing refractive index fluids using the Kramers-Kronig relationsTianqi Sai, Matthias Saba, Eric Dufresne, Ulrich Steiner and Bodo D. WiltsFaraday Discussions, vol. 223, pp. 136-144, Royal Society of Chemistry, 2020.
For a number of optical applications, it is advantageous to precisely tune the refractive index of a liquid. Here, we harness a well-established concept in optics for this purpose. The Kramers-Kronig relation provides a physical connection between the spectral variation of the (real) refractive index and the absorption coefficient. In particular, a sharp spectral variation of the absorption coefficient gives rise to either an enhancement or reduction of the refractive index in the spectral vicinity of this variation. By using bright commodity dyes that fulfil this absorption requirement, we demonstrate the use of the Kramers-Kronig relation to predictively obtain refractive index values in water solutions that are otherwise only attained with toxic specialised liquids.
- Temporal Control of Soft Materials with Chemical ClocksGuido Panzarasa and Eric DufresneChimia, vol. 74: no. 7, pp. 612-612, Swiss Chemical Society, 2020.
- Clocking the Clock: Programmable Acid Autocatalysis in the Chlorite‐Tetrathionate ReactionGuido PanzarasaChemistrySelect, vol. 5: no. 27, pp. 8074-8077, Wiley, 2020.
Acid-autocatalyzed clock reactions are chemical systems able to suddenly lower pH after a certain time. They would be useful to program self-assembly of pH-responsive building blocks if factors such as the starting pH, the magnitude and time of pH decrease could be flexibly tailored. Here, we show how to control these parameters in the chlorite-tetrathionate (CT) clock reaction using cyclic esters, such as δ-gluconolactone (GL) and 1,3-propanesultone (PrS), as in situ slow acid generators. © 2020 Wiley
- Elastic stresses reverse Ostwald ripeningKathryn A. Rosowski, Estefania Vidal-Henriquez, David Zwicker, Robert W. Style and Eric DufresneSoft Matter, vol. 16: no. 25, pp. 5892-5897, Royal Society of Chemistry, 2020.
When liquid droplets nucleate and grow in a polymer network, compressive stresses can significantly increase their internal pressure, reaching values that far exceed the Laplace pressure. When droplets have grown in a polymer network with a stiffness gradient, droplets in relatively stiff regions of the network tend to dissolve, favoring growth of droplets in softer regions. Here, we show that this elastic ripening can be strong enough to reverse the direction of Ostwald ripening: large droplets can shrink to feed the growth of smaller ones. To numerically model these experiments, we generalize the theory of elastic ripening to account for gradients in solubility alongside gradients in mechanical stiffness.
- Switchable adhesion of soft composites induced by a magnetic fieldPaolo Testa, Benoît Chappuis, Sabrina Kistler, Robert W. Style, Laura J. Heyderman and Eric DufresneSoft Matter, vol. 16: no. 25, pp. 5806-5811, Royal Society of Chemistry, 2020.
Switchable adhesives have the potential to improve the manufacturing and recycling of parts, and to enable new modes of motility for soft robots. Here, we demonstrate magnetically-switchable adhesion of a two-phase composite to non-magnetic objects. The composite's continuous phase is a silicone elastomer, and the dispersed phase is a magneto-rheological fluid. The composite is simple to prepare, and to mold into different shapes. When a magnetic field is applied, the magneto-rheological fluid develops a yield stress, which dramatically enhances the composite's adhesive properties. We demonstrate up to a nine-fold increase of the pull-off force of non-magnetic objects in the presence of a 250 mT field.
- Oscillating Reactions Meet Polymers at InterfacesAlina Osypova, Matthias Dübner and Guido PanzarasaMaterials, vol. 13: no. 13, pp. 2957, MDPI, 2020.
Chemo-mechanical phenomena, including oscillations and peristaltic motions, are widespread in nature—just think of heartbeats—thanks to the ability of living organisms to convert directly chemical energy into mechanical work. Their imitation with artificial systems is still an open challenge. Chemical clocks and oscillators (such as the popular Belousov–Zhabotinsky (BZ) reaction) are reaction networks characterized by the emergence of peculiar spatiotemporal dynamics. Their application to polymers at interfaces (grafted chains, layer-by-layer assemblies, and polymer brushes) offers great opportunities for developing novel smart biomimetic materials. Despite the wide field of potential applications, limited research has been carried out so far. Here, we aim to showcase the state-of-the-art of this fascinating field of investigation, highlighting the potential for future developments and providing a personal outlook.
- Small-scale demixing in confluent biological tissuesPreeti Sahu, Daniel M. Sussman, Matthias Rübsam, Aaron F. Mertz, Valerie Horsley, Eric Dufresne, Carien M. Niessen, M. Cristina Marchetti, M. Lisa Manning and Jen M. SchwarzSoft Matter, vol. 16: no. 13, pp. 3325-3337, Springer, 2020.
- Elastic ripening and inhibition of liquid-liquid phase separationKathryn A. Rosowski, Tianqi Sai, Estefania Vidal-Henriquez, David Zwicker, Robert W. Style and Eric DufresneNature Physics, vol. 16: no. 4, pp. 422-425, Nature, 2020.
- Extreme cavity expansion in soft solids: Damage without fractureJin Y. Kim, Zezhou Liu, Byung M. Weon, Tal Cohen, Chung-Yuen Hui, Eric Dufresne and Robert W. StyleScience Advances, vol. 6: no. 13, pp. eaaz0418, AAAS, 2020.
Cavitation is a common damage mechanism in soft solids. Here, we study this using a phase separation technique in stretched, elastic solids to controllably nucleate and grow small cavities by several orders of magnitude. The ability to make stable cavities of different sizes, as well as the huge range of accessible strains, allows us to systematically study the early stages of cavity expansion. Cavities grow in a scale-free manner, accompanied by irreversible bond breakage that is distributed around the growing cavity rather than being localized to a crack tip. Furthermore, cavities appear to grow at constant driving pressure. This has strong analogies with the plasticity that occurs surrounding a growing void in ductile metals. In particular, we find that, although elastomers are normally considered as brittle materials, small-scale cavity expansion is more like a ductile process. Our results have broad implications for understanding and controlling failure in soft solids.
- Supramolecular assembly by time-programmed acid autocatalysisGuido Panzarasa, Tianqi Sai, Alexandre Torzynski, Katrina Smith-Mannschott and Eric DufresneMolecular Systems Design & Engineering, vol. 5: no. 2, pp. 445-448, Royal Society of Chemistry, 2020.
Autocatalytic pH clocks can be useful to control self-assembly in the time domain. Their applications are, however, limited by the currently available toolbox. We describe here an approach for the design of a dynamic pH switch that generates intense alkali-to-acid changes after a tailorable lagtime (from minutes to hours), and we demonstrate its application for the time-controlled supramolecular self-assembly of nanofibers.
- Transient supramolecular assembly of a functional perylene diimide controlled by a programmable pH cycleGuido Panzarasa, Alexandre Torzynski, Tianqi Sai, Katrina Smith-Mannschott and Eric DufresneSoft Matter, vol. 16: no. 3, pp. 591-594, Royal Society of Chemistry, 2020.
Self-regulating materials require embedded control systems. Active networks of enzymes fulfill this function in living organisms, and the development of chemical controls for synthetic systems is still in its infancy. While previous work has focused on enzymatic controls, small-molecule networks have unexplored potential. We describe a simple small-molecule network that is able to produce transient pH cycles with tunable lagtimes and lifetimes, based on coupling the acid-to-alkali methylene glycol-sulfite reaction to 1,3-propanesultone, a slow acid generator. Applied to transient pH-driven supramolecular self-assembly of a perylene diimide, our system matches the flexibility of in vitro enzymatic systems, including the ability to perform repeated cycles of assembly and disassembly.
2019
- Magnetically Addressable Shape‐Memory and Stiffening in a Composite ElastomerPaolo Testa, Robert W. Style, Jizhai Cui, Claire Donnelly, Elena Borisova, Peter M. Derlet, Eric Dufresne and Laura J. HeydermanAdvanced Materials, vol. 31: no. 29, pp. 1900561, Wiley, 2019.
- Functional optimality of the sulcus pattern of the human brainStefanie Heyden and Michael OrtizMathematical Medicine and Biology, vol. 36: no. 2, pp. 207-221, Oxford University Press, 2019.
We develop a mathematical model of information transmission across the biological neural network of the human brain. The overall function of the brain consists of the emergent processes resulting from the spread of information through the neural network. The capacity of the brain is therefore related to the rate at which it can transmit information through the neural network. The particular transmission model under consideration allows for information to be transmitted along multiple paths between points of the cortex. The resulting transmission rates are governed by potential theory. According to this theory, the brain has preferred and quantized transmission modes that correspond to eigenfunctions of the classical Steklov eigenvalue problem, with the reciprocal eigenvalues quantifying the corresponding transmission rates. We take the model as a basis for testing the hypothesis that the sulcus pattern of the human brain has evolved to maximize the rate of transmission of information between points in the cerebral cortex. We show that the introduction of sulci, or cuts, in an otherwise smooth domain indeed increases the overall transmission rate. We demonstrate this result by means of numerical experiments concerned with a spherical domain with a varying number of slits on its surface.
- Non-invasive in vivo quantification of human skin tension linesDanielle Laiacona, Joshua Cohen, Kerianne Coulon, Zachary W. Lipsky, Christopher H. Maiorana, Rostislav Boltyanskiy, Eric Dufresne and Guy K. GermanActa Biomaterialia, vol. 88, pp. 141-148, Elsevier, 2019.
- Effects of strain-dependent surface stress on the adhesive contact of a rigid sphere to a compliant substrateZezhou Liu, Katharine E. Jensen, Qin Xu, Robert W. Style, Eric Dufresne, Anand Jagota and Chung-Yuen HuiSoft Matter, vol. 15: no. 10, pp. 2223-2231, Royal Society of Chemistry, 2019.
- When Black and White make Green: the Surprising Interplay of Structure and PigmentsTianqi Sai, Bodo D. Wilts, Alba Sicher, Ullrich Steiner, Frank Scheffold and Eric DufresneChimia, vol. 73: no. 1, pp. 47-50, Swiss Chemical Society, 2019.
- Singular dynamics in the failure of soft adhesive contactsJustin D. Berman, Manjari Randeria, Robert W. Style, Qin Xu, James R. Nichols, Aidan J. Duncan, Michael Loewenberg, Eric Dufresne and Katharine E. JensenSoft Matter, vol. 15: no. 6, pp. 1327-1334, Royal Society of Chemistry, 2019.
- Impact of in situ acid generation and iodine sequestration on the chlorite-iodide clock reactionGuido Panzarasa and Eric DufresneChaos, vol. 29: no. 7, pp. 071102, American Institute of Physics, 2019.
2018
- Optimizing information transmission rates drives brain gyrificationStefanie Heyden and Michael OrtizProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 474: no. 2219, pp. 20180527, Royal Society, 2018.
We investigate the functional optimality of the cerebral cortex of an adult human brain geometry. Unlike most competing models, we postulate that the cerebral cortex formation is driven by the objective of maximizing the total information transmission rate. Starting from a random path model, we show that this optimization problem is related to the Steklov eigenvalue problem. Combining realistic brain geometries with the finite-element method, we calculate the underlying Steklov eigenvalues and eigenfunctions. By comparison to a convex hull approximation, we show that the adult human brain geometry indeed reduces the Steklov eigenvalue spectrum and thus increases the rate at which information is exchanged between points on the cerebral cortex. With a view to possible clinical applications, the leading Steklov eigenfunctions and the resulting induced magnetic fields are computed and reported.
- Controlled formation of chitosan particles by a clock reactionGuido Panzarasa, Alina Osypova, Alba Sicher, Arie Bruinink and Eric DufresneSoft Matter, vol. 14: no. 31, pp. 6415-6418, Royal Society of Chemistry, 2018.
- The contact mechanics challenge: tribology meets soft matterRobert W. Style, Brandon A. Krick, Katharine E. Jensen and W. Gregory SawyerSoft Matter, vol. 14: no. 28, pp. 5706-5709, Royal Society of Chemistry, 2018.
- The mechanical equilibrium of soft solids with surface elasticityRobert W. Style and Qin XuSoft Matter, vol. 14: no. 22, pp. 4569-4576, Royal Society of Chemistry, 2018.
- Turbulent shear layers in confining channelsGraham P. Benham, Alfonso A. Castrejon-Pita, Ian J. Hewitt, Colin P. Please, Rob W. Style and Paul A.D. BirdJournal of Turbulence, vol. 19: no. 6, pp. 431-445, Taylor & Francis, 2018.
- The Anomalous Yield Behavior of Fused Silica GlassWilliam Schill, Stefanie Heyden, Sergio Conti and Michael OrtizJournal of the Mechanics and Physics of Solids, vol. 113, pp. 105-125, Elsevier, 2018.
We develop a critical-state model of fused silica plasticity on the basis of data mined from molecular dynamics (MD) calculations. The MD data is suggestive of an irreversible densification transition in volumetric compression resulting in permanent, or plastic, densification upon unloading. The MD data also reveals an evolution towards a critical state of constant volume under pressure-shear deformation. The trend towards constant volume is from above, when the glass is overconsolidated, or from below, when it is underconsolidated. We show that these characteristic behaviors are well-captured by a critical state model of plasticity, where the densification law for glass takes the place of the classical consolidation law of granular media and the locus of constant-volume states defines the critical-state line. A salient feature of the critical-state line of fused silica, as identified from the MD data, that renders its yield behavior anomalous is that it is strongly non-convex, owing to the existence of two well-differentiated phases at low and high pressures. We argue that this strong non-convexity of yield explains the patterning that is observed in molecular dynamics calculations of amorphous solids deforming in shear. We employ an explicit and exact rank-2 envelope construction to upscale the microscopic critical-state model to the macroscale. Remarkably, owing to the equilibrium constraint the resulting effective macroscopic behavior is still characterized by a non-convex critical-state line. Despite this lack of convexity, the effective macroscopic model is stable against microstructure formation and defines well-posed boundary-value problems.
- Surface elastic constants of a soft solidQin Xu, Robert W. Style and Eric DufresneSoft Matter, vol. 14: no. 6, pp. 916-920, Royal Society of Chemistry, 2018.
- Liquid-Liquid Phase Separation in an Elastic NetworkRobert W. Style, Tianqi Sai, Nicoló Fanelli, Mahdiye Ijavi, Katrina Smith-Mannschott, Qin Xu, Lawrence A. Wilen and Eric DufresnePhysical Review X, vol. 8: no. 1, pp. 011028, American Physical Society, 2018.
Living and engineered systems rely on the stable coexistence of two interspersed liquid phases. Yet, surface tension drives their complete separation. Here, we show that stable droplets of uniform and tunable size can be produced through arrested phase separation in an elastic matrix. Starting with a cross-linked, elastic polymer network swollen by a solvent mixture, we change the temperature or composition to drive demixing. Droplets nucleate and grow to a stable size that is tunable by the network cross-linking density, the cooling rate, and the composition of the solvent mixture. We discuss thermodynamic and mechanical constraints on the process. In particular, we show that the threshold for macroscopic phase separation is altered by the elasticity of the polymer network, and we highlight the role of correlations between nuclei positions in determining the droplet size and polydispersity. This phenomenon has potential applications ranging from colloid synthesis and structural color to phase separation in biological cells.
- Vinculin and the mechanical response of adherent fibroblasts to matrix deformationKathryn A. Rosowski, Rostislav Boltyanskiy, Yingjie Xiang, Koen Van den Dries, Martin A. Schwartz and Eric DufresneScientific Reports, vol. 8: no. 1, pp. 17967, Nature, 2018.
Cells respond to the mechanics of their environment. Mechanical cues include extracellular matrix (ECM) stiffness and deformation, which are primarily sensed through integrin-mediated adhesions. We investigated the impact of ECM deformation on cellular forces, measuring the time-evolution of traction forces of isolated mouse fibroblasts in response to stretch and release. Stretch triggered a marked increase of traction stresses and apparent stiffness. Expression of the focal adhesion protein vinculin not only increased baseline traction forces, but also increased dissipation of mechanical energy, which was correlated with the cells’ failure to recover baseline traction forces after release of stretch.
2017
- Indentation of a floating elastic sheet: Geometry versus applied tensionFinn Box, Dominic Vella, Robert W. Style and Jerome A. NeufeldProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 473: no. 2206, pp. 20170335, Royal Society, 2017.
The localized loading of an elastic sheet floating on a liquid bath occurs at scales from a frog sitting on a lily pad to a volcano supported by the Earth’s tectonic plates. The load is supported by a combination of the stresses within the sheet (which may include applied tensions from, for example, surface tension) and the hydrostatic pressure in the liquid. At the same time, the sheet deforms, and may wrinkle, because of the load. We study this problem in terms of the (relatively weak) applied tension and the indentation depth. For small indentation depths, we find that the force–indentation curve is linear with a stiffness that we characterize in terms of the applied tension and bending stiffness of the sheet. At larger indentations, the force–indentation curve becomes nonlinear and the sheet is subject to a wrinkling instability. We study this wrinkling instability close to the buckling threshold and calculate both the number of wrinkles at onset and the indentation depth at onset, comparing our theoretical results with experiments. Finally, we contrast our results with those previously reported for very thin, highly bendable membranes.
- Direct measurement of strain-dependent solid surface stressQin Xu, Katharine E. Jensen, Rostislav Boltyanskiy, Raphaël Sarfati, Robert W. Style and Eric DufresneNature Communications, vol. 8, pp. 555, Nature, 2017.
Surface stress, also known as surface tension, is a fundamental material property of any interface. However, measurements of solid surface stress in traditional engineering materials, such as metals and oxides, have proven to be very challenging. Consequently, our understanding relies heavily on untested theories, especially regarding the strain dependence of this property. Here, we take advantage of the high compliance and large elastic deformability of a soft polymer gel to directly measure solid surface stress as a function of strain. As anticipated by theoretical work for metals, we find that the surface stress depends on the strain via a surface modulus. Remarkably, the surface modulus of our soft gels is many times larger than the zero-strain surface tension. This suggests that surface stresses can play a dominant role in solid mechanics at larger length scales than previously anticipated.
- Elastocapillarity: Surface Tension and the Mechanics of Soft SolidsRobert W. Style, Anand Jagota, Chung-Yuen Hui and Eric DufresneAnnual Review of Condensed Matter Physics, vol. 8, pp. 99-118, Annual Reviews, 2017.
- Vancomycin Reduces Cell Wall Stiffness and Slows Swim Speed of the Lyme Disease BacteriumMichael W. Harman, Alex E. Hamby, Ross Boltyanskiy, Alexia A. Belperron, Linda K. Bockenstedt, Holger Kress, Eric Dufresne and Charles W. WolgemuthBiophysical Journal, vol. 112: no. 4, pp. 746-754, Cell Press, 2017.
- Tracking particles with large displacements using energy minimizationRostislav Boltyanskiy, Jason W. Merrill and Eric DufresneSoft Matter, vol. 13: no. 11, pp. 2201-2206, Royal Society of Chemistry, 2017.
- Maximum likelihood estimations of force and mobility from single short Brownian trajectoriesRaphael Sarfati, Jerzy Bławzdziewicz and Eric DufresneSoft Matter, vol. 13: no. 11, pp. 2174-2180, Royal Society of Chemistry, 2017.
- Investigation of the influence of viscoelasticity on oncotripsyStefanie Heyden and Michael OrtizComputer Methods in Applied Mechanics and Engineering, vol. 314, pp. 314-322, Elsevier, 2017.
Oncotripsy has recently been proposed as a means of selectively targeting cancer cells via resonant harmonic excitation (Heyden and Ortiz, 2016). The method makes use of aberrations in material properties of cancerous cells which allow to induce local resonance up to membrane lysis in cancerous cells while leaving healthy cells intact. Here, we explore the influence of viscoelasticity on the oncotripsy effect. Based on Rayleigh damping, we derive viscoelastic target frequencies and simulate the fully nonlinear transient response of healthy and cancerous cells at resonance. Results confirm the viability of oncotripsy with viscoelastic material behavior of cell constituents accounted for.
- Mechanical stability of particle-stabilized droplets under micropipette aspirationNiveditha Samudrala, Jin Nam, Raphael Sarfati, Robert W. Style and Eric DufresnePhysical Review E, vol. 95: no. 1, pp. 012805-1-012805-5, American Physical Society, 2017.
- Strain-Dependent Solid Surface Stress and the Stiffness of Soft ContactsKatharine E. Jensen, Robert W. Style, Qin Xu and Eric DufresnePhysical Review X, vol. 7: no. 4, pp. 041031, American Physical Society, 2017.
Surface stresses have recently emerged as a key player in the mechanics of highly compliant solids. The classic theories of contact mechanics describe adhesion with a compliant substrate as a competition between surface energies driving deformation to establish contact and bulk elasticity resisting this. However, it has recently been shown that surface stresses provide an additional restoring force that can compete with and even dominate over elasticity in highly compliant materials, especially when length scales are small compared to the ratio of the surface stress to the elastic modulus, Υ/E. Here, we investigate experimentally the contribution of surface stresses to the total force of adhesion. We find that the elastic and capillary contributions to the adhesive force are of similar magnitude and that both are required to account for measured adhesive forces between rigid silica spheres and compliant, silicone gels. Notably, the strain dependence of the solid surface stress contributes to the stiffness of soft solid contacts at leading order.
- E-cadherin integrates mechanotransduction and EGFR signaling to control junctional tissue polarization and tight junction positioningMatthias Rübsam, Aaron F. Mertz, Akiharu Kubo, Susanna Marg, Christian Jüngst, Gladiola Goranci-Buzhala, Astrid C. Schauss, Valerie Horsley, Eric Dufresne, Markus Moser, Wolfgang Ziegler, Masayuki Amagai, Sara A. Wickström and Carien M. NiessenNature Communications, vol. 8, pp. 1250, Nature, 2017.
Generation of a barrier in multi-layered epithelia like the epidermis requires restricted positioning of functional tight junctions (TJ) to the most suprabasal viable layer. This positioning necessitates tissue-level polarization of junctions and the cytoskeleton through unknown mechanisms. Using quantitative whole-mount imaging, genetic ablation, and traction force microscopy and atomic force microscopy, we find that ubiquitously localized E-cadherin coordinates tissue polarization of tension-bearing adherens junction (AJ) and F-actin organization to allow formation of an apical TJ network only in the uppermost viable layer. Molecularly, E-cadherin localizes and tunes EGFR activity and junctional tension to inhibit premature TJ complex formation in lower layers while promoting increased tension and TJ stability in the granular layer 2. In conclusion, our data identify an E-cadherin-dependent mechanical circuit that integrates adhesion, contractile forces and biochemical signaling to drive the polarized organization of junctional tension necessary to build an in vivo epithelial barrier.
- Local Arp2/3 dependent actin assembly modulates applied traction force during apCAM adhesion site maturationKenneth B. Buck, Andrew W. Schaefer, Vincent T. Schoonderwoert, Matthew S. Creamer, Eric Dufresne and Paul ForscherMolecular Biology of the Cell, vol. 28: no. 1, pp. 98-110, American Society for Cell Biology, 2017.
Homophilic binding of immunoglobulin superfamily molecules such as the Aplysia cell adhesion molecule (apCAM) leads to actin filament assembly near nascent adhesion sites. Such actin assembly can generate significant localized forces that have not been characterized in the larger context of axon growth and guidance. We used apCAM-coated bead substrates applied to the surface of neuronal growth cones to characterize the development of forces evoked by varying stiffness of mechanical restraint. Unrestrained bead propulsion matched or exceeded rates of retrograde network flow and was dependent on Arp2/3 complex activity. Analysis of growth cone forces applied to beads at low stiffness of restraint revealed switching between two states: frictional coupling to retrograde flow and Arp2/3-dependent propulsion. Stiff mechanical restraint led to formation of an extensive actin cup matching the geometric profile of the bead target and forward growth cone translocation; pharmacological inhibition of the Arp2/3 complex or Rac attenuated F-actin assembly near bead binding sites, decreased the efficacy of growth responses, and blocked accumulation of signaling molecules associated with nascent adhesions. These studies introduce a new model for regulation of traction force in which local actin assembly forces buffer nascent adhesion sites from the mechanical effects of retrograde flow.
2016
- All-atom molecular dynamics simulations of multiphase segregated polyurea under quasistatic uniaxial compressionStefanie Heyden, Michael Ortiz and Alessandro FortunelliPolymer, vol. 106, pp. 100-108, Elsevier, 2016.
We present an approach to model the mechanical response of multiphase segregated polyurea under large quasistatic uniaxial compression. The approach is based on a two-step procedure. We first conduct all-atom NVE molecular dynamics simulations of the fully-mixed and hard phases of polyurea. We then put forth a model of hard-phase activation based on Taylor, or meanfield, averaging and compute the composite response. The predictions of the present approach, with or without Taylor averaging, show remarkable agreement with data from plate-impact experiments.
- It's Harder to Splash on Soft SolidsChristopher J. Howland, Arnaud Antkowiak, J. Rafael Castrejón-Pita, Sam D. Howison, James M. Oliver, Robert Style and Alfonso A. Castrejón-PitaPhysical Review Letters, vol. 117: no. 18, pp. 184502, American Physical Society, 2016.
Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact. We find that solids with Young’s moduli ≲ 100 kPa reduce splashing, in agreement with simple scaling arguments. Thus, materials like soft gels and elastomers can be used as simple coatings for effective splash prevention. Soft substrates also serve as a useful system for testing splash-formation theories and sheet-ejection mechanisms, as they allow the characteristics of ejection sheets to be controlled independently of the bulk impact dynamics of droplets.
- Long-range attraction of particles adhered to lipid vesiclesRaphael Sarfati and Eric DufresnePhysical Review E, vol. 94: no. 1, pp. 012604, American Physical Society, 2016.
- Oncotripsy: Targeting cancer cells selectively via resonant harmonic excitationStefanie Heyden and Michael OrtizJournal of the Mechanics and Physics of Solids, vol. 92, pp. 164-175, Elsevier, 2016.
We investigate a method of selectively targeting cancer cells by means of ultrasound harmonic excitation at their resonance frequency, which we refer to as oncotripsy. The geometric model of the cells takes into account the cytoplasm, nucleus and nucleolus, as well as the plasma membrane and nuclear envelope. Material properties are varied within a pathophysiologically-relevant range. A first modal analysis reveals the existence of a spectral gap between the natural frequencies and, most importantly, resonant growth rates of healthy and cancerous cells. The results of the modal analysis are verified by simulating the fully-nonlinear transient response of healthy and cancerous cells at resonance. The fully nonlinear analysis confirms that cancerous cells can be selectively taken to lysis by the application of carefully tuned ultrasound harmonic excitation while simultaneously leaving healthy cells intact.
- Domain morphology, boundaries, and topological defects in biophotonic gyroid nanostructures of butterfly wing scalesAndrej Singer, Leandra Boucheron, Sebastian H. Dietze, Katharine E. Jensen, David Vine, Ian McNulty, Eric Dufresne, Richard O. Prum, Simon G.J. Mochrie and Oleg G. ShpyrkoScience Advances, vol. 2: no. 6, pp. e1600149, AAAS, 2016.
Many organisms in nature have evolved sophisticated cellular mechanisms to produce photonic nanostructures and, in recent years, diverse crystalline symmetries have been identified and related to macroscopic optical properties. However, because we know little about the distributions of domain sizes, the orientations of photonic crystals, and the nature of defects in these structures, we are unable to make the connection between the nanostructure and its development and functionality. We report on nondestructive studies of the morphology of chitinous photonic crystals in butterfly wing scales. Using spatially and angularly resolved x-ray diffraction, we find that the domains are highly oriented with respect to the whole scale, indicating growth from scale boundaries. X-ray coherent diffractive imaging reveals two types of crystalline domain interfaces: abrupt changes between domains emerging from distinct nucleation sites and smooth transitions with edge dislocations presumably resulting from internal stresses during nanostructure development. Our study of the scale structure reveals new aspects of photonic crystal growth in butterfly wings and shows their similarity to block copolymer materials. It opens new avenues to exploration of fundamental processes underlying the growth of biological photonic nanostructures in a variety of species.
- Note: An iterative algorithm to improve colloidal particle locatingKatharine E. Jensen and Nobuo NakamuraReview of Scientific Instruments, vol. 87: no. 6, pp. 066103, American Institute of Physics, 2016.
- Fluctuations and correlations of emission from random lasersJason W. Merrill, Hui Cao and Eric DufresnePhysical Review A, vol. 93: no. 2, pp. 021801, American Physical Society, 2016.
- Surface tension and the Mori-Tanaka theory of non-dilute soft composite solidsFrancesco Mancarella, Robert W. Style and John S. WettlauferProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 472: no. 2196, pp. 20150853, Royal Society, 2016.
- Interfacial tension and a three-phase generalized self-consistent theory of non-dilute soft composite solidsFrancesco Mancarella, Robert W. Style and John S. WettlauferSoft Matter, vol. 12: no. 10, pp. 2744-2750, Royal Society of Chemistry, 2016.
- Large Deformations of a Soft Porous MaterialChristopher W. MacMinn, Eric Dufresne and John S. WettlauferPhysical Review Applied, vol. 5: no. 4, pp. 044020, American Physical Society, 2016.
- Solid capillarity: when and how does surface tension deform soft solids?Bruno Andreotti, Oliver Bäumchen, François Boulogne, Karen E. Daniels, Eric Dufresne, Hugo Perrin, Thomas Salez, Jacco H. Snoeijer and Robert W. StyleSoft Matter, vol. 12: no. 12, pp. 2993-2996, Royal Society of Chemistry, 2016.
- Combinatorial Strategies for Synthesis and Characterization of Alloy Microstructures over Large Compositional RangesYanglin Li, Katharine E. Jensen, Yanhui Liu, Jingbei Liu, Pan Gong, Ellen B. Scanley, Christine C. Broadbridge and Jan SchroersACS Combinatorial Science, vol. 18, pp. 630-637, American Chemical Society, 2016.
- Segregated Ice Growth in a Suspension of Colloidal ParticlesJulia M.H. Schollick, Robert W. Style, Arran Curran, John S. Wettlaufer, Eric Dufresne, Patrick B. Warren, Krassimir P. Velikov, Roel P.A. Dullens and Dirk G.A.L. AartsThe Journal of Physical Chemistry B, vol. 120: no. 16, pp. 3941-3949, American Chemical Society, 2016.
2015
- Material modeling of cardiac valve tissue: Experiments, constitutive analysis and numerical investigationStefanie Heyden, Andreas Nagler, Cristóbal Bertoglio, Jonas Biehler, Michael W. Gee, Wolfgang A. Wall and Michael OrtizJournal of Biomechanics, vol. 48: no. 16, pp. 4287-4296, Elsevier, 2015.
A key element of the cardiac cycle of the human heart is the opening and closing of the four valves. However, the material properties of the leaflet tissues, which fundamentally contribute to determine the mechanical response of the valves, are still an open field of research. The main contribution of the present study is to provide a complete experimental data set for porcine heart valve samples spanning all valve and leaflet types under tensile loading. The tests show a fair degree of reproducibility and are clearly indicative of a number of fundamental tissue properties, including a progressively stiffening response with increasing elongation. We then propose a simple anisotropic constitutive model, which is fitted to the experimental data set, showing a reasonable interspecimen variability. Furthermore, we present a dynamic finite element analysis of the aortic valve to show the direct usability of the obtained material parameters in computational simulations.
- Wetting and Phase Separation in Soft AdhesionKatharine E. Jensen, Raphael Sarfati, Robert W. Style, Rostislav Boltyanskiy, Aditi Chakrabarti, Manoj K. Chaudhury and Eric DufresneProceedings of the National Academy of Sciences of the United States of America, vol. 112: no. 47, pp. 14490-14494, National Academy of Sciences, 2015.
- A nonlocal model of fracture by crazing in polymersStefanie Heyden, Sergio Conti and Michael OrtizMechanics of Materials, vol. 90, pp. 131-139, Elsevier, 2015.
We derive and numerically verify scaling laws for the macroscopic fracture energy of polymers undergoing crazing from a micromechanical model of damage. The model posits a local energy density that generalizes the classical network theory of polymers so as to account for chain failure and a nonlocal regularization based on strain-gradient elasticity. We specifically consider periodic deformations of a slab subject to prescribed opening displacements on its surfaces. Based on the growth properties of the energy densities, scaling relations for the local and nonlocal energies and for the specific fracture energy are derived. We present finite-element calculations that bear out the heuristic scaling relations.
- Soft microcapsules with highly plastic shells formed by interfacial polyelectrolyte-nanoparticle complexationGilad Kaufman, Siamak Nejati, Raphael Sarfati, Rostislav Boltyanskiy, Michael Loewenberg, Eric Dufresne and Chinedum O. OsujiSoft Matter, vol. 11: no. 38, pp. 7478-7482, Royal Society of Chemistry, 2015.
- Adsorption of soft particles at fluid interfacesRobert W. Style, Lucio Isa and Eric DufresneSoft Matter, vol. 11: no. 37, pp. 7412-7419, Royal Society of Chemistry, 2015.
- Edges of human embryonic stem cell colonies display distinct mechanical properties and differentiation potentialKathryn A. Rosowski, Aaron F. Mertz, Samuel Norcross, Eric Dufresne and Valerie HorsleyScientific Reports, vol. 5, pp. 14218, Nature, 2015.
In order to understand the mechanisms that guide cell fate decisions during early human development, we closely examined the differentiation process in adherent colonies of human embryonic stem cells (hESCs). Live imaging of the differentiation process reveals that cells on the outer edge of the undifferentiated colony begin to differentiate first and remain on the perimeter of the colony to eventually form a band of differentiation. Strikingly, this band is of constant width in all colonies, independent of their size. Cells at the edge of undifferentiated colonies show distinct actin organization, greater myosin activity and stronger traction forces compared to cells in the interior of the colony. Increasing the number of cells at the edge of colonies by plating small colonies can increase differentiation efficiency. Our results suggest that human developmental decisions are influenced by cellular environments and can be dictated by colony geometry of hESCs.
- Intrinsic fluctuations and driven response of insect swarmsRui Ni, James G. Puckett, Eric Dufresne and Nicholas T. OuellettePhysical Review Letters, vol. 115: no. 11, pp. 118104, American Physical Society, 2015.
- Structural Diversity of Arthropod Biohotonic Nanostructures Spans Amphiphilic Phase SpaceVinodkumar Saranathan, Ainsley E. Seago, Alec Sandy, Suresh Narayanan, Chinedum O. Osuji, Simon G.J. Mochrie, Hui Cao, Eric Dufresne and Richard O. PrumNano Letters, vol. 15: no. 6, pp. 3735-3742, American Chemical Society, 2015.
- Computational Simulation, Multiscale Computations, and Issues Related to Behavioral Aspects of High Strain-Rate Elastomeric PolymersStefanie Heyden and Michael OrtizIn Elastomeric Polymers with High Rate Sensitivity, edited by Barsoum, Roshdy George, pp. 256-263, Amsterdam: William Andrew, 2015.
- Surface tension and the mechanics of liquid inclusions in compliant solidsRobert W. Style, John S. Wettlaufer and Eric DufresneSoft Matter, vol. 11: no. 4, pp. 672-679, Royal Society of Chemistry, 2015.
- A micromechanical damage and fracture model for polymers based on fractional strain-gradient elasticityStefanie Heyden, Bo Li, Kerstin Weinberg, Sergio Conti and Michael OrtizJournal of the Mechanics and Physics of Solids, vol. 74, pp. 175-195, Elsevier, 2015.
We formulate a simple one-parameter macroscopic model of distributed damage and fracture of polymers that is amenable to a straightforward and efficient numerical implementation. We show that the macroscopic model can be rigorously derived, in the sense of optimal scaling, from a micromechanical model of chain elasticity and failure regularized by means of fractional strain-gradient elasticity. In particular, we derive optimal scaling laws that supply a link between the single parameter of the macroscopic model, namely, the critical energy-release rate of the material, and micromechanical parameters pertaining to the elasticity and strength of the polymer chains and to the strain-gradient elasticity regularization. We show how the critical energy-release rate of specific materials can be determined from test data. Finally, we demonstrate the scope and fidelity of the model by means of an example of application, namely, Taylor-impact experiments of polyurea 1000 rods.
- Stiffening solids with liquid inclusionsRobert W. Style, Rostislav Boltyanskiy, Benjamin Allen, Katharine E. Jensen, Henry P. Foote, John S. Wettlaufer and Eric DufresneNature Physics, vol. 11, pp. 82-87, Nature, 2015.
- Fluid-Driven Deformation of a Soft-Granular MaterialChristopher W. MacMinn, Eric Dufresne and John S. WettlauferPhysical Review X, vol. 5: no. 1, pp. 011020, American Physical Society, 2015.
Compressing a porous, fluid-filled material drives the interstitial fluid out of the pore space, as when squeezing water out of a kitchen sponge. Inversely, injecting fluid into a porous material can deform the solid structure, as when fracturing a shale for natural gas recovery. These poromechanical interactions play an important role in geological and biological systems across a wide range of scales, from the propagation of magma through Earth’s mantle to the transport of fluid through living cells and tissues. The theory of poroelasticity has been largely successful in modeling poromechanical behavior in relatively simple systems, but this continuum theory is fundamentally limited by our understanding of the pore-scale interactions between the fluid and the solid, and these problems are notoriously difficult to study in a laboratory setting. Here, we present a high-resolution measurement of injection-driven poromechanical deformation in a system with granular microsctructure: We inject fluid into a dense, confined monolayer of soft particles and use particle tracking to reveal the dynamics of the multiscale deformation field. We find that a continuum model based on poroelasticity theory captures certain macroscopic features of the deformation, but the particle-scale deformation field exhibits dramatic departures from smooth, continuum behavior. We observe particle-scale rearrangement and hysteresis, as well as petal-like mesoscale structures that are connected to material failure through spiral shear banding.
2014
- Mechanotransduction and extracellular matrix homeostasisJay D. Humphrey, Eric Dufresne and Martin A. SchwartzNature Reviews Molecular Cell Biology, vol. 15: no. 12, pp. 802-812, Nature, 2014.
- Single-step microfluidic fabrication of soft monodisperse polyelectrolyte microcapsules by interfacial complexationGilad Kaufman, Rostislav Boltyanskiy, Siamak Nejati, Abdou R. Thiam, Michael Loewenberg, Eric Dufresne and Chinedum O. OsujiLab on a Chip, vol. 14: no. 18, pp. 3494-3497, Royal Society of Chemistry, 2014.
- Traction force microscopy in physics and biologyRobert W. Style, Rostislav Boltyanskiy, Guy K. German, Callen Hyland, Christopher W. MacMinn, Aaron F. Mertz, Larry A. Wilen, Ye Xu and Eric DufresneSoft Matter, vol. 10: no. 23, pp. 4047-4055, Royal Society of Chemistry, 2014.
- Dynamic peripheral traction forces balance stable neurite tension in regenerating Aplysia bag cell neuronsCallen Hyland, Aaron F. Mertz, Paul Forscher and Eric DufresneScientific Reports, vol. 4, pp. 4961, Nature, 2014.
Growth cones of elongating neurites exert force against the external environment, but little is known about the role of force in outgrowth or its relationship to the mechanical organization of neurons. We used traction force microscopy to examine patterns of force in growth cones of regenerating Aplysia bag cell neurons. We find that traction is highest in the peripheral actin-rich domain and internal stress reaches a plateau near the transition between peripheral and central microtubule-rich domains. Integrating stress over the area of the growth cone reveals that total scalar force increases with area but net tension on the neurite does not. Tensions fall within a limited range while a substantial fraction of the total force can be balanced locally within the growth cone. Although traction continuously redistributes during extension and retraction of the peripheral domain, tension is stable over time, suggesting that tension is a tightly regulated property of the neurite independent of growth cone dynamics. We observe that redistribution of traction in the peripheral domain can reorient the end of the neurite shaft. This suggests a role for off-axis force in growth cone turning and neuronal guidance.
- Regeneration of Aplysia Bag Cell Neurons is Synergistically Enhanced by Substrate-Bound Hemolymph Proteins and LamininCallen Hyland, Eric Dufresne and Paul ForscherScientific Reports, vol. 4, pp. 4617, Nature, 2014.
We have investigated Aplysia hemolymph as a source of endogenous factors to promote regeneration of bag cell neurons. We describe a novel synergistic effect between substrate-bound hemolymph proteins and laminin. This combination increased outgrowth and branching relative to either laminin or hemolymph alone. Notably, the addition of hemolymph to laminin substrates accelerated growth cone migration rate over ten-fold. Our results indicate that the active factor is either a high molecular weight protein or protein complex and is not the respiratory protein hemocyanin. Substrate-bound factor(s) from central nervous system-conditioned media also had a synergistic effect with laminin, suggesting a possible cooperation between humoral proteins and nervous system extracellular matrix. Further molecular characterization of active factors and their cellular targets is warranted on account of the magnitude of the effects reported here and their potential relevance for nervous system repair.
- Adsorption of Sub-Micron Amphiphilic Dumbbells to Fluid InterfacesLucio Isa, Niveditha Samudrala and Eric DufresneLangmuir, vol. 30: no. 18, pp. 5057-5063, American Chemical Society, 2014.
- The Bacterial Cytoplasm Has Glass-like Properties and Is Fluidized by Metabolic ActivityBradley R. Parry, Ivan V. Surovtsev, Matthew T. Cabeen, Corey S. O’Hern, Eric Dufresne and Christine Jacobs-WagnerCell, vol. 156: no. 1-2, pp. 183-194, Cell Press, 2014.
2013
- Elastic Coupling of Nascent apCAM Adhesions to Flowing Actin NetworksCecile O. Mejean, Andrew W. Schaefer, Kenneth B. Buck, Holger Kress, Alla Shundrovsky, Jason W. Merrill, Eric Dufresne and Paul ForscherPLoS ONE, vol. 8: no. 9, pp. e73389, PLOS, 2013.
Adhesions are multi-molecular complexes that transmit forces generated by a cell’s acto-myosin networks to external substrates. While the physical properties of some of the individual components of adhesions have been carefully characterized, the mechanics of the coupling between the cytoskeleton and the adhesion site as a whole are just beginning to be revealed. We characterized the mechanics of nascent adhesions mediated by the immunoglobulin-family cell adhesion molecule apCAM, which is known to interact with actin filaments. Using simultaneous visualization of actin flow and quantification of forces transmitted to apCAM-coated beads restrained with an optical trap, we found that adhesions are dynamic structures capable of transmitting a wide range of forces. For forces in the picoNewton scale, the nascent adhesions’ mechanical properties are dominated by an elastic structure which can be reversibly deformed by up to 1 µm. Large reversible deformations rule out an interface between substrate and cytoskeleton that is dominated by a number of stiff molecular springs in parallel, and favor a compliant cross-linked network. Such a compliant structure may increase the lifetime of a nascent adhesion, facilitating signaling and reinforcement.
- Surfactant treatments influence drying mechanics in human stratum corneumGuy K. German, E. Pashkovski and Eric DufresneJournal of Biomechanics, vol. 46: no. 13, pp. 2145-2151, Elsevier, 2013.
- Cell migration: Towards the voidEric Dufresne and Martin A. SchwartzNature Materials, vol. 12, pp. 783-784, Nature, 2013.
- Patterning droplets with durotaxisRobert W. Style, Yonglu Che, Su Ji Park, Byung Mook Weon, Jung Ho Je, Callen Hyland, Guy K. German, Michael P. Power, Larry A. Wilen, John S. Wettlaufer and Eric DufresneProceedings of the National Academy of Sciences of the United States of America, vol. 110: no. 31, pp. 12541-12544, National Academy of Sciences, 2013.
- Low-loss high-speed speckle reduction using a colloidal dispersionBrandon Redding, Graham Allen, Eric Dufresne and Hui CaoApplied Optics, vol. 52: no. 6, pp. 1168-1172, OSA Publishing, 2013.
- Universal deformation of soft substrates near a contact line and the direct measurement of solid surface stressesRobert W. Style, Rostislav Boltyanskiy, Yonglu Che, J.S. Wettlaufer, Larry A. Wilen and Eric DufresnePhysical Review Letters, vol. 110: no. 6, pp. 066103-1-066103-5, American Physical Society, 2013.
- Imaging stress and strain in the fracture of drying colloidal filmsYe Xu, Guy K. German, Aaron F. Mertz and Eric DufresneSoft Matter, vol. 9: no. 14, pp. 3735-3740, Royal Society of Chemistry, 2013.
- Cadherin-based intercellular adhesions organize epithelial cell-matrix traction forcesAaron F. Mertz, Yonglu Che, Shiladitya Banerjee, Jill M. Goldstein, Kathryn A. Rosowski, Stephen F. Revilla, Carien M. Niessen, M. Christina Marchetti, Eric Dufresne and Valerie HorsleyProceedings of the National Academy of Sciences of the United States of America, vol. 110: no. 3, pp. 842-7, National Academy of Sciences, 2013.
- Surface tension and contact with soft elastic solidsRobert W. Style, Callen Hyland, Rostislav Boltyanskiy, John S. Wettlaufer and Eric DufresneNature Communications, vol. 4, pp. 2728, Nature, 2013.
2012
- Structure and optical function of amorphous photonic nanostructures from avian feather barbs: a comparative small angle X-ray scattering (SAXS) analysis of 230 bird speciesVinodkumar Saranathan, Jason D. Forster, Heeso Noh, Seng Fatt Liew, Simon G.J. Mochrie, Hui Cao, Eric Dufresne and Richard O. PrumJournal of the Royal Society. Interface, vol. 9: no. 75, pp. 2563-2580, Royal Society, 2012.
- A modular approach to the design of protein-based smart gelsTijana Z. Grove, Jason Forster, Genaro Pimienta, Eric Dufresne and Lynne ReganBiopolymers, vol. 97: no. 7, pp. 508-517, Wiley-Blackwell, 2012.
- Static wetting on deformable substrates, from liquids to soft solidsRobert W. Style and Eric DufresneSoft Matter, vol. 8: no. 27, pp. 7177-7184, Royal Society of Chemistry, 2012.
- Heterogeneous drying stresses in stratum corneumGuy K. German, W.C. Engl, E. Pashkovski, S. Banerjee, Y. Xu, Aaron F. Mertz, Callen Hyland and Eric DufresneBiophysical Journal, vol. 102: no. 11, pp. 2424-2432, Cell Press, 2012.
- Scaling of traction forces with the size of cohesive cell coloniesAaron F. Mertz, Shiladitya Banerjee, Yonglu Che, Guy K. German, Ye Xu, Callen Hyland, M. Christina Marchetti, Valerie Horsley and Eric DufresnePhysical Review Letters, vol. 108: no. 19, pp. 198101, American Physical Society, 2012.
- Membrane tension maintains cell polarity by confining signals to the leading edge during neutrophil migrationAndrew R. Houk, Alexandra Jilkine, Cecile O. Mejean, Rostislav Boltyanskiy, Eric Dufresne, Sigurd B. Angenent, Steven J. Altschuler, Lani F. Wu and Orion D. WeinerCell, vol. 148: no. 1-2, pp. 175-188, Cell Press, 2012.
2011
- Photonic band gaps in three-dimensional network structures with short-range orderSeng Fatt Liew, Jin-Kyu Yang, Heeso Noh, Carl Schreck, Eric Dufresne, Corey S. O'Hern and Hui CaoPhysical Review A, vol. 84: no. 6, pp. 063818, American Physical Society, 2011.
- Short-range order and near-field effects on optical scattering and structural colorationSeng Fatt Liew, Jason Forster, Heeso Noh, Carl F. Schreck, Vinod Saranathan, Xinhui Lu, Lin Yang, Richard O. Prum, Corey S. O'Hern, Eric Dufresne and Hui CaoOptics Express, vol. 19: no. 9, pp. 8208-8217, OSA Publishing, 2011.
- Assembly of Optical-Scale Dumbbells into Dense Photonic CrystalsJason D. Forster, Jin-Gyu Park, Manish Mittal, Heeso Noh, Carl F. Schreck, Corey S. O'Hern, Hui Cao, Erich M. Furst and Eric DufresneACS Nano, vol. 5: no. 8, pp. 6695-6700, American Chemical Society, 2011.
- Grasshoppers alter jumping biomechanics to enhance escape performance under chronic risk of spider predationDror Hawlena, Holger Kress, Eric Dufresne and Oswald J. SchmitzFunctional Ecology, vol. 25, pp. 279-288, Wiley-Blackwell, 2011.
- Deformation of an elastic substrate by a three-phase contact lineElizabeth R. Jerison, Ye Xu, Larry A. Wilen and Eric DufresnePhysical Review Letters, vol. 106, pp. 186103, American Physical Society, 2011.
2010
- How Noniridescent Colors Are Generated by Quasi-ordered Structures of Bird FeathersHeeso Noh, Seng Fatt Liew, Vinodkumar Saranathan, Simon G.J. Mochrie, Richard O. Prum, Eric Dufresne and Cao HuiAdvanced Materials, vol. 22: no. 26-27, pp. 2871-2880, Wiley-VCH, 2010.
- Many-body force and mobility measurements in colloidal systemsJason W. Merrill, Sunil K. Sainis, Jerzy Blawzdziewicz and Eric DufresneSoft Matter, vol. 6: no. 10, pp. 2187-2192, Royal Society of Chemistry, 2010.
- Imaging in-plane and normal stresses near an interface crack using traction force microscopyYe Xu, Wilfried C. Engl, Elizabeth R. Jerison, Kevin J. Wallenstein, Callen Hyland, Larry A. Wilen and Eric DufresneProceedings of the National Academy of Sciences of the United States of America, vol. 107: no. 34, pp. 14964-14967, National Academy of Sciences, 2010.
- Stimuli-responsive smart gels realized via modular protein designTijana Z. Grove, Chinedum O. Osuji, Jason D. Forster, Eric Dufresne and Lynne ReganJournal of the American Chemical Society, vol. 132: no. 40, pp. 14024-14026, American Chemical Society, 2010.
- Contribution of double scattering to structural coloration in quasiordered nanostructures of bird feathersHeeso Noh, Seng F. Liew, Vinodkumar Saranathan, Richard O. Prum, Simon G.J. Mochrie, Eric Dufresne and Hui CaoPhysical Review E, vol. 81, pp. 51923, American Physical Society, 2010.
- High-yield synthesis of monodisperse dumbbell-shaped polymer nanoparticlesJin-Gyu Park, Jason D. Forster and Eric DufresneJournal of the American Chemical Society, vol. 132: no. 17, pp. 5960-5961, American Chemical Society, 2010.
- Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scalesVinodkumar Saranathan, Chinedum O. Osuji, Simon G.J. Mochrie, Heeso Noh, Suresh Narayanan, Alec Sandy, Eric Dufresne and Richard O. PrumProceedings of the National Academy of Sciences of the United States of America, vol. 107: no. 26, pp. 11676-11681, National Academy of Sciences, 2010.
- Biomimetic isotropic nanostructures for structural colorationJason D. Forster, Heeso Noh, Seng F. Liew, Vinodkumar Saranathan, Schreck. Carl F., Lin Yang, Jin-Gyu Park, Richard O. Prum, Simon G.J. Mochrie, Corey S. O'Hern, Hui Cao and Eric DufresneAdvanced Materials, vol. 22, pp. 2939-44, Wiley-VCH, 2010.
- Double scattering of light from Biophotonic Nanostructures with short-range orderHeeso Noh, Seng Fatt Liew, Vinodkumar Saranathan, Richard O. Prum, Simon G.J. Mochrie, Eric Dufresne and Hui CaoOptics Express, vol. 18: no. 11, pp. 11942-11948, OSA Publishing, 2010.
2009
- Many-Body Electrostatic Forces between Colloidal Particles at Vanishing Ionic StrengthJason W. Merrill, Sunil K. Sainis and Eric DufresnePhysical Review Letters, vol. 103: no. 13, pp. 138301-1-138301-4, American Physical Society, 2009.
- Synthesis of colloidal particles with the symmetry of water moleculesJin-Gyu Park, Jason D. Forster and Eric DufresneLangmuir, vol. 25: no. 16, pp. 8903-8906, American Chemical Society, 2009.
- Self-assembly of amorphous biophotonic nanostructures by phase separationEric Dufresne, Heeso Noh, Vinodkumar Saranathan, Simon G.J. Mochrie, Hui Cao and Richard O. PrumSoft Matter, vol. 5: no. 9, pp. 1792-1795, Royal Society of Chemistry, 2009.
- Mechanical properties of individual microgel particles through the deswelling transitionSara M. Hashmi and Eric DufresneSoft Matter, vol. 5: no. 19, pp. 3682-3688, Royal Society of Chemistry, 2009.
- Cell stimulation with optically manipulated microsourcesHolger Kress, Jin-Gyu Park, Cecile O. Mejean, Jason D. Forster, Jason Park, Spencer S. Walse, Yong Zhang, Dianqing Wu, Orion D. Weiner, Tarek M. Fahmy and Eric DufresneNature Methods, vol. 6, pp. 905-9, Nature, 2009.
- Development of Color Producing β-keratin Nanostructures in Avian Feather BarbsRichard O. Prum, Eric Dufresne, Tim Quinn and Karla WatersJournal of the Royal Society. Interface, vol. 6: no. 2009, pp. S253-S265, Royal Society, 2009.
- Multiplexed force measurements on live cells with holographic optical tweezersCecile O. Mejean, Andrew W. Schaefer, Eleanor A. Millman, Paul Forscher and Eric DufresneOptics Express, vol. 17: no. 8, pp. 6209-6217, OSA Publishing, 2009.
2008
- Electrostatic Interactions of Colloidal Particles at Vanishing Ionic StrengthSunil K. Sainis, Jason W. Merrill and Eric DufresneLangmuir, vol. 24: no. 23, pp. 13334-13347, American Chemical Society, 2008.
- Minimal model for kinetic arrestPampa Pal, Corey S. O'Hern, Jerzy Blawzdziewicz, Eric Dufresne and Robin StinchcombePhysical Review E, vol. 78: no. 1, pp. 11111, American Physical Society, 2008.
- Electrostatic interactions of colloidal particles in nonpolar solvents: role of surface chemistry and charge control agentsSunil K. Sainis, Vincent Germain, Cecile O. Mejean and Eric DufresneLangmuir, vol. 24: no. 4, pp. 1160-1164, American Chemical Society, 2008.
2007
- Statistics of particle trajectories at short time intervals reveal fN-scale colloidal forcesSunil K. Sainis, Vincent Germain and Eric DufresnePhysical Review Letters, vol. 99: no. 1, pp. 018303-1-018303-4, American Physical Society, 2007.
- Spatially extended FCS for visualizing and quantifying high-speed multiphase flows in microchannelsSara M. Hashmi, Michael Loewenberg and Eric DufresneOptics Express, vol. 15: no. 10, pp. 6528-6533, Optical Society of America, 2007.
2006
- Dynamics of fracture in drying suspensionsEric Dufresne, D.J. Stark, N.A. Greenblatt, Jixin Cheng, John W. Hutchinson, Lakshminarayana Mahadevan and David A. WeitzLangmuir, vol. 22: no. 17, pp. 7144-7147, American Chemical Society, 2006.
- Observation of plasmon propagation, redirection, and fan-out in silver nanowiresAric W. Sanders, David A. Routenberg, Benjamin J. Wiley, Younan Xia, Eric Dufresne and Mark A. ReedNano Letters, vol. 6: no. 8, pp. 1822-1826, American Chemical Society, 2006.
- Automated trapping, assembly, and sorting with holographic optical tweezersStephen C. Chapin, Vincent Germain and Eric DufresneOptics Express, vol. 14: no. 26, pp. 13095-13100, Optical Society of America, 2006.
2005
- Charge stabilization in nonpolar solventsMing F. Hsu, Eric Dufresne and David A. WeitzLangmuir, vol. 21, pp. 4881-4887, American Chemical Society, 2005.
- Onset of buckling in drying droplets of colloidal suspensionsNicolas Tsapis, Eric Dufresne, Shrabani S. Sinha, Christophe S. Riera, John W. Hutchinson, Lakshminarayana Mahadevan and David A. WeitzPhysical Review Letters, vol. 94: no. 1, pp. 18302, American Physical Society, 2005.
2003
2002
2001
- Computer-generated holographic optical tweezer arraysEric Dufresne, Gabriel C. Spalding, Matthew T. Dearing, Steven A. Sheets and David G. GrierReview of Scientific Instruments, vol. 72: no. 3, pp. 1810-1816, American Institute of Physics, 2001.
- Brownian dynamics of a sphere between parallel wallsEric Dufresne, D. Altman and David G. GrierEurophysics Letters, vol. 53: no. 2, pp. 264-270, IOP Publishing, 2001.
2000
1999
1998
- Optical tweezer arrays and optical substrates created with diffractive opticsEric Dufresne and David G. GrierReview of Scientific Instruments, vol. 69: no. 5, pp. 1974-1977, American Institute of Physics, 1998.
- Photoexcited Fe2O3 Surfaces: Properties and ChemisorptionD.S. Toledano, Eric Dufresne and V.E. HenrichJournal of Vacuum Science & Technology A, vol. 16: no. 3, pp. 1050-1054, American Institute of Physics, 1998.