1Rising global demand for potable water is driving innovation in water treatment 2 methods. Shock electrodialysis is a recently proposed technique that exploits deioniza-3 tion shock waves in porous media to purify water. In this letter, we present the first 4 continuous and scalable shock electrodialysis system and demonstrate the separation 5 of sodium, chloride, and other ions from a feed stream. Our prototype continuously 6 removes over 99% (and up to 99.99%) of salt from diverse electrolytes over a range 7 of concentrations (1 mM, 10 mM, and 100 mM). The desalination data collapses with 8 dimensionless current, scaled to charge advection in the feed stream. Enhanced water 9 recovery with increasing current (up to 79%) is a fortuitous discovery, which we at-

SignificanceViscous fingering commonly takes place during injection of one fluid that displaces a resident fluid in a porous medium. Fingering normally is promoted where the injected fluid is less viscous than the resident fluid being displaced. We propose a design of a porous medium in the form of an ordered structure to suppress or trigger (depending on the application) viscous fingering in porous media without modifying fluid properties or wettability. We utilize pore-scale direct numerical simulations, state-of-art experiments and analysis to derive predictive tools to evaluate effects of various parameters on controlling viscous fingering in porous media. Moreover, we propose generalized analytical solutions and a phase diagram for the parameter space affecting viscous fingering patterns.

Hydrogels hold promise in agriculture as reservoirs of water in dry soil, potentially alleviating the burden of irrigation. However, confinement in soil can markedly reduce the ability of hydrogels to absorb water and swell, limiting their widespread adoption. Unfortunately, the underlying reason remains unknown. By directly visualizing the swelling of hydrogels confined in three-dimensional granular media, we demonstrate that the extent of hydrogel swelling is determined by the competition between the force exerted by the hydrogel due to osmotic swelling and the confining force transmitted by the surrounding grains. Furthermore, the medium can itself be restructured by hydrogel swelling, as set by the balance between the osmotic swelling force, the confining force, and intergrain friction. Together, our results provide quantitative principles to predict how hydrogels behave in confinement, potentially improving their use in agriculture as well as informing other applications such as oil recovery, construction, mechanobiology, and filtration.

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Proteostasis in the cytosol is governed by the heat shock response. The master regulator of the heat shock response, heat shock factor 1 (HSF1), and key chaperones whose levels are HSF1-regulated have emerged as high-profile targets for therapeutic applications ranging from protein misfolding-related disorders to cancer. Nonetheless, a generally applicable methodology to selectively and potently inhibit endogenous HSF1 in a small molecule-dependent manner in disease model systems remains elusive. Also problematic, the administration of even highly selective chaperone inhibitors often has the side effect of activating HSF1 and thereby inducing a compensatory heat shock response. Herein, we report a ligand-regulatable, dominant negative version of HSF1 that addresses these issues. Our approach, which required engineering a new dominant negative HSF1 variant, permits doseable inhibition of endogenous HSF1 with a selective small molecule in cell-based model systems of interest. The methodology allows us to uncouple the pleiotropic effects of chaperone inhibitors and environmental toxins from the concomitantly induced compensatory heat shock response. Integration of our method with techniques to activate HSF1 enables the creation of cell lines in which the cytosolic proteostasis network can be up- or down-regulated by orthogonal small molecules. Selective, small molecule-mediated inhibition of HSF1 has distinctive implications for the proteostasis of both chaperone-dependent globular proteins and aggregation-prone intrinsically disordered proteins. Altogether, this work provides critical methods for continued exploration of the biological roles of HSF1 and the therapeutic potential of heat shock response modulation.

Capillary fingering is a displacement process that can occur when a non-wetting fluid displaces a wetting fluid from a homogeneous disordered porous medium. Here, we investigate how this process is influenced by a pore size gradient. Using microfluidic experiments and computational porenetwork models, we show that the non-wetting fluid displacement behavior depends sensitively on the direction and the magnitude of the gradient. The fluid displacement depends on the competition between a pore size gradient and pore-scale disorder; indeed, a sufficiently large gradient can completely suppress capillary fingering. By analyzing capillary forces at the pore scale, we identify a non-dimensional parameter that describes the physics underlying these diverse flow behaviors.Our results thus expand the understanding of flow in complex porous media, and suggest a new way to control flow behavior via the introduction of pore size gradients.

Many clays, soils, biological tissues, foods, and coatings are shrinkable, granular materials: they are composed of packed, hydrated grains that shrink when dried. In many cases, these packings crack during drying, critically hindering applications. However, while cracking has been widely studied for bulk gels and packings of non-shrinkable grains, little is known about how packings of shrinkable grains crack. Here, we elucidate how grain shrinkage alters cracking during drying. Using experiments with model shrinkable hydrogel beads, we show that differential shrinkage can dramatically alter crack evolution during drying-in some cases, even causing cracks to spontaneously "self-close". In other cases, packings shrink without cracking or crack irreversibly. We developed both granular and continuum models to quantify the interplay between grain shrinkage, poromechanics, packing size, drying rate, capillarity, and substrate friction on cracking. Guided by the theory, we also found that cracking can be completely altered by varying the spatial profile of drying. Our work elucidates the rich physics underlying cracking in shrinkable, granular packings, and yields new strategies for controlling crack evolution.Experiments on model shrinkable grains reveal a range of cracking behaviors during drying: shrinkage without cracking, irreversible cracking, and most remarkably, reversible cracking in

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