Eric Dufresne

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Dufresne

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Eric

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0000-0002-3091-5039

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Publications 1 - 10 of 153

Structural color from pigment-loaded nanostructures
Sai, Tianqi; Froufe-Pérez, Luis S.; Scheffold, Frank; et al. (2023)
Soft Matter
Color can originate from wavelength-dependence in the absorption of pigments or the scattering of nanostructures. While synthetic colors are dominated by the former, vivid structural colors found in nature have inspired much research on the latter. However, many of the most vibrant colors in nature involve the interactions of structure and pigment. Here, we demonstrate that pigment can be exploited to efficiently create bright structural color at wavelengths outside its absorption band. We created pigment-enhanced Bragg reflectors by sequentially spin-coating layers of poly-vinyl alcohol (PVA) and polystyrene (PS) loaded with β-carotene (BC). With only 10 double layers, we achieved a peak reflectance over 0.8 at 550 nm and normal incidence. A pigment-free multilayer made of the same materials would require 25 double layers to achieve the same reflectance. Further, pigment loading suppressed the Bragg reflector's characteristic iridescence. Using numerical simulations, we further show that similar pigment loadings could significantly expand the gamut of non-iridescent colors addressable by photonic glasses.
Local Arp2/3 dependent actin assembly modulates applied traction force during apCAM adhesion site maturation
Buck, Kenneth B.; Schaefer, Andrew W.; Schoonderwoert, Vincent T.; et al. (2017)
Molecular Biology of the Cell
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.
A modular approach to the design of protein-based smart gels
Grove, Tijana Z.; Forster, Jason; Pimienta, Genaro; et al. (2012)
Biopolymers
Elastic stresses reverse Ostwald ripening
Rosowski, Kathryn A.; Vidal-Henriquez, Estefania; Zwicker, David; et al. (2020)
Soft Matter
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.
Multiplexed force measurements on live cells with holographic optical tweezers
Mejean, Cecile O.; Schaefer, Andrew W.; Millman, Eleanor A.; et al. (2009)
Optics Express
Dynamic Shape Modulation of Deflated and Adhered Lipid Vesicles
Wolfisberg , Gianna; Agudo-Canalejo , Jaime; Bittmann , Pablo C.; et al. (2025)
Journal of the American Chemical Society
Lipid membrane-bounded organelles often possess intricate morphologies with spatially varying curvatures and large membrane surface areas relative to internal volume (small reduced volumes). These features are thought to be essential for protein sorting and vesicle trafficking, but challenging to reproduce in vitro. Here, we show that weakly adhered giant unilamellar vesicles (GUVs) can be osmotically deflated to reduced volumes as low as 0.1, similar to what is found in flattened, disc-shaped organelles such as Golgi cisternae and ER sheets. Using shape analysis with the Canham-Helfrich model, we determine mechanical parameters including adhesion strength, membrane tension, and pressure of individual vesicles. We find that the rate of shape flattening during deflation is governed by a normalized adhesion strength that combines vesicle size, adhesion energy, and bending rigidity. For highly flattened disc-like vesicles, we identify a geometric relationship that allows the adhesion strength to be estimated solely from the vesicle’s aspect ratio, size, and bending rigidity. These results provide a quantitative experimental platform for bottom-up studies of membrane shaping mechanisms and shape-dependent phenomena, such as curvature-mediated protein sorting.
Solid capillarity: when and how does surface tension deform soft solids?
Andreotti, Bruno; Bäumchen, Oliver; Boulogne, François; et al. (2016)
Soft Matter
Soft microcapsules with highly plastic shells formed by interfacial polyelectrolyte-nanoparticle complexation
Kaufman, Gilad; Nejati, Siamak; Sarfati, Raphael; et al. (2015)
Soft Matter
Ice and air: Visualisation of freezing spread and freeze-thaw embolism in young Liriodendron tulipifera leaves
Johnson, Kate M.; Scherer, Muriel; Gerber, Dominic; et al. (2025)
Journal of Experimental Botany
Spring freezing is an unforgiving stress for young leaves, often leading to death and with consequences for tree productivity and survival. While both the water-transport system and living tissues are vulnerable to freezing, we do not currently know whether damage to one or both of these systems causes death in leaves exposed to freezing. In this study, whole saplings of Liriodendron tulipifera were exposed to freezing and thawing trajectories designed to mimic natural spring freezes. We monitored the formation of freeze-thaw xylem embolism and damage to photosynthetic tissues and found a predictable progression of ice formation across the leaf surface that was strongly influenced by leaf- vein architecture, notably the presence or absence of bundle-sheath extensions. Our results also showed that freeze-thaw embolism occurred only in the lowest vein orders where mean vessel diameter exceeded 30μm. With evidence of both freeze-thaw embolism and damage to photosynthetic tissue, we conclude that this dual-mode of lethality in leaves might be common among other wide-vesseled angiosperm leaves, potentially playing a role in limiting geographic distributions, and demonstrate that bundle sheath extensions might stall or even prevent freezing spread.
Amino acids modulate liquid-liquid phase separation in vitro and in vivo by regulating protein-protein interactions
Xu, Xufeng; Rebane, Aleksander; Roset Julia, Laura; et al. (2024)
Proceedings of the National Academy of Sciences of the United States of America
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.

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Eric Dufresne

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