First Cohort of CSLM Postdoctoral Fellows

The Center for Soft and Living Matter is proud to announce the selection of the first cohort of CSLM Postdoctoral Fellows. Congratulations to our fellows!

Tissues with Tensions

A model of epithelial tissues with edge tensions

Physical Learning Network

Learning modifies a physical learning network. a) Input forces (black) are applied to the physical degrees of freedom (green, e.g. node positions) of a physical network (e.g. mechanical spring network), whose interactions correspond to learning degrees of freedom (blue, e.g. spring constants). b) In the physical configuration space, this input force causes the system to respond, equilibrating in a free state (red dot). To train the system, a further `output force’ is applied, nudging the system to a clamped state (green dot). The blue arrows describe the inherent physical coordinate system, with direction corresponding to eigenmodes v of the physical Hessian H, and lengths correspond to the associated inverse eigenvalues. c) A local learning rule is applied, modifying the learning degrees of freedom. On top of improving the system free state response, learning tends to rotate the Hessian coordinate system such that the eigenmode corresponding to the lower eigenvalues align with the free state response, and decrease these eigenvalues. d) Training results in a physical system whose lower eigenvalues are reduced, and eigenmodes aligned with the trained task(s). The system responds considerably more strongly to random forces, shown by the area spanned by the trained inverse eigenvalues (blue ellipse) compared to the untrained ones (red ellipse). Training makes the physical system more conductive and lower dimensional.

An Electronic Physical Learning Network in Action

Cryo-electron Tomography

Cryo-electron tomography unveils the intricate molecular structural details in situ at the tip of a frozen parasite cell.

Cooperative Clusters

Cooperative clusters of immune cells (pink) form when engulfing cancer cells (green).By Dr. Larry Dooling, Discher Lab (Nature Biomed Eng’g 2023)

High Interfacial Tension

Fat droplets (yellow) within cells collide with the nucleus (white) and rupture it (red), and droplet roundness indicates high interfacial tension. By Dr. Irena Ivanovska and Michael Tobin, Discher Lab (J Cell Biology 2023).

Foam Reconstruction

A 2-dimensional foam of wet soap bubbles squashed between glass plates, after 10 hours of coarsening by the diffusion of gas from smaller to larger bubbles. The green curves are circular arcs, fit to the Plateau borders that connect adjacent three-fold vertices; the red curves represent uncertainty in their curvature. For scale, each Plateau border is 1/3 mm across. The entire image is 2.3 cm x 1.6 cm.

From Photon to Neuron

The neural synapse between a rod photoreceptor (right) and its bipolar cell (left). Art by David M. Goodsell. 

Hydrodynamic Communication Between Cells

Cellular communities of the protist Spirostomum ambiguum use hydrodynamic trigger waves to communicate with each other. Spirostomum can contract its body length by 60% within milliseconds, creating accelerations that can reach forces of 14g and generating long-ranged vortex flows that trigger neighboring Spirostomum cells to contract. The connecting lines and colors indicate which cells triggered which other cells.

Inorganic Chemistry Cover Image

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A paramagnetic CoII4 capsule binds xenon, which is stably encapsulated in the solid state through hydrogen-bonding interactions of the capsule with guanidinium cations. Rapid exchange of xenon in solution enables ultrasensitive 129Xe NMR sensing applications.

Responsive and Foldable Soft Materials

In this image, a biomimetic lotus is gradually blooming, which is made from stimuli-responsive soft materials with folding properties from 2D to 3D, leading to a variety of potential applications including biomimetic machines, wearable electronics, drug delivery and soft robotics. Different types of responsive materials with folding properties are summarized in the review article by J. Liu,Y. Gao, Y-J. Lee, S. Yang*, Trends Chem.2, 107–122 (2020).

Biopolymer Network

A biopolymer network with stiff inclusions responds to uniaxial compression. Compressed network fibers are colored orange and stretched network fibers are colored blue. Under small compressions, the network fibers bend and the sample first softens then stiffens with increasing compression (right). Further increasing compression leads to rearrangement of the stiff inclusions, driving stretching of fibers (middle) and leading to a crossover from bending-dominated to stretching-dominated mechanics and increasing stiffness. With sufficiently large compression the inclusions jam (left), increasing the stiffness still further.

Cytoskeletal Filaments

Cytoskeletal filaments inside the leading edge of a frozen-hydrated human cell imaged by cryo-electron tomography.

Image taken by Dr. Longsheng Lai from the Yi-Wei Chang lab in the Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania

Vascular Networks of Leaves

Morphological transition in growing adaptive flow networks such as the vascular networks of leaves. Line width is proportional to the quarter root of the conductance, color indicates the pressure p. (top left) Initially the network is disordered and not hierarchically organized, with many long branches connecting directly to the source. (top right) Hierarchical organization begins to appear. (lower left) The network is hierarchically organized and efficient. Few long branches are visible (compare with (top left)). (lower right) Optimal network when the source is at the boundary, showing leaf-like main and secondary veins.

Machine-learned softness as a predictor of dynamics in glassy liquids

As liquids are cooled towards their glass transitions, they exhibit dramatically more sluggish and heterogeneous dynamics. One notorious stumbling block in understanding this behavior has been the inability to identify structural features corresponding to the dynamics. We use machine learning methods to construct a structural quantity that correlates strongly with dynamics. We call this quantity “softness”—particles with high softness are highly vulnerable to rearrangement, while those with low softness are resistant. Here we show results from a simulation of a liquid near the glass transition, in which particles with high softness (and corresponding high dynamical mobility) are opaque and colored while particles with low softness are translucent and black. The image was constructed from a two-dimensional slab of the system rendered in POVRAY and then processed with a color gradient.

Shear Band

Characterizing structural inhomogeneity is an essential step in understanding the mechanical response of amorphous materials. We introduce a threshold-free measure based on the field of vectors pointing from the center of each particle to the centroid of the Voronoi cell in which the particle resides. These vectors tend to point in toward regions of high free volume and away from regions of low free volume, reminiscent of sinks and sources in a vector field. The divergence of this vector field correlates with rearrangements, as in the shear band pictured here for a 2d system of bidisperse grains.

Welcome to the Center for Soft and Living Matter at the University of Pennsylvania!

Penn / Philly skyline

This interdisciplinary center brings together more than 60 faculty working on soft and living matter from more than 10 departments across the Penn campus, from the School of Arts and Sciences as well as the School of Engineering and Applied Sciences.

The intellectual richness, reach and applications of the field make it an exciting one that has grown (and continues to grow) rapidly in many science and engineering departments across the country.  The field appeals to many universities because it is highly interdisciplinary and is linked strongly to the discovery of new phenomena and the development of new materials, techniques and applications.

Penn has long been an intellectual center for soft and living matter and was among the first universities to invest seriously in the field. Nowhere else has there been a comparable investment in soft-to-living matter across departments and schools. As a result, Penn has been at the forefront of the field for the last 15 years. It boasts many distinguished faculty members across the relevant departments who have reaped multiple awards and honors and have helped set intellectual agendas across campus. As an example, the Laboratory for Research on the Structure of Matter (LRSM) has included a significant number of soft/living matter researchers since its inception more than 60 years ago. Since then, the LRSM has been continuously funded by the NSF for collaborative research. This has fostered a culture of collaboration across disciplines in soft and living matter at Penn that is unmatched anywhere.

soft matter yodh

Soft Matter

Soft matter research encompasses the study of collective phenomena in many-body systems in which quantum mechanics does not play an explicit role. The intellectual territory spanned by soft matter is vast in its reach. It covers the range of length scales from nanometer-sized liquid crystals or particles to geological features such as craters and river networks. Some of the biggest outstanding challenges in the sciences—to understand emergent collective phenomena in strongly-correlated many-body systems that are not crystalline, that are far out of equilibrium, that have nonlinear responses or that are designed either by humans or by natural evolutionary processes to have special properties or functions, for example—are confronted in their purest forms in this area. These scientific challenges underlie some of the most exciting, high-profile and societally-important areas in engineering, ranging from nanomaterials, biomaterials/bioengineering and energy applications such as batteries and fuel cells to robotics and data science.

Living Matter

Areas that have long been regarded as interface topics between different fields of science or engineering with biology, such as biophysics, biomathematics, bioengineering and quantitative biology, are increasingly recognized as sharing common preoccupations that tie them together into a field of their own, living matter. The phenomena of life pose challenges to our understanding of strongly-correlated many-body systems that range far beyond those typically encountered in non-living systems. To improve the ability of organisms to survive, interactions among the many components comprising living systems have been tuned by the process of evolution to lead to biological functions of great specificity, precision and complexity that are unmatched by properties of human-made materials.  This poses fundamentally new scientific questions. The answers to these questions have great societal relevance through medicine and engineering. Like soft matter, the systems needed to sustain life range in size from the nanoscale to the geological scale. Living systems typically operate at relatively high temperatures, so quantum phenomena play a minor role. As a result, the fields of living and soft matter are closely intertwined. Researchers wander freely and frequently between soft and living matter, carrying experimental, computational and theoretical tools, concepts and questions in both directions. Over the years, they have constructed a continuum of research spanning between soft and living matter science and engineering.

Interested in Joining Us?

The Center welcomes prospective graduate students and postdocs. Interested prospective graduate students must apply to departments, not directly to the center, but are free to work with faculty in other departments. Each department has a “graduate group” of faculty who can work with graduate students in that department. The graduate group includes faculty from other departments, and it is straightforward to add faculty who are not already members of the graduate group. All graduate students working with center faculty are encouraged to participate in Center activities to benefit further from the rich intellectual and collaborative atmosphere fostered by the Center.

Distinguished Faculty

Our participants are comprised of many distinguished faculty members across the relevant departments who have reaped multiple awards and honors and have helped set intellectual agendas across campus.