Active and Driven Soft Matter

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TECHNICAL SUMMARYThis award supports theoretical research and education in soft condensed matter and biological physics, specifically in the field of driven and active matter. The name "active matter" has recently been coined to refer to soft materials composed of many interacting units that individually consume energy and collectively generate motion or mechanical stresses. Examples include bacterial suspensions, the cytoskeleton of living cells, collections of cells on a substrate or in a soft elastic matrix, and even monolayers of vibrated granular rods. These systems exhibit large-scale emergent behavior with transitions between ordered and disordered states, pattern formation, and novel rheological and mechanical properties. They can be described theoretically as a new "living" soft material using the tools of condensed matter and statistical physics. A major objective of the project is disentangling the role of purely physical interactions, such as excluded volume effects or medium-mediated hydrodynamic couplings, from that of genetically of biochemically-regulated signaling or of external symmetry-breaking effects, such as chemotaxis, in controlling the emergent behavior of collections of living organisms. This important question has implications ranging from the understanding of biofilm formation to the modeling of wound healing and tissue formation. The award supports research to: (1) use analogies with magnetic and liquid crystalline systems to model pattern formation and swarming in collections of swimming micro-organisms, understand the rheology of these living systems, and investigate the similarities between collections of living and inanimate self-propelled units; (2) model the behavior of motile cells on soft substrates or in three-dimensional gels, with the goal of understanding the role of the matrix or substrate elasticity in controlling collective cell migration, organization and sorting, ultimately leading to tissue formation; (3) understand transport in conventional soft matter, such as colloidal gels and glasses, that is driven out of equilibrium by an external force, such as an electric field, and where translational invariance is broken by material disorder. Members of underrepresented groups and undergraduate students will be actively recruited to participate in this research project. NON-TECHNICAL SUMMARYThis award supports theoretical research and education in soft condensed matter and biological physics, specifically in the field of driven and active matter. The name "active matter" has recently been coined to refer to soft materials composed of many interacting units that individually consume energy and collectively generate motion or mechanical stresses. Examples include bacterial suspensions, the cytoskeleton of living cells, collections of cells on a substrate or in a soft elastic matrix, and even monolayers of vibrated granular rods. These systems exhibit large-scale phenomena and novel mechanical properties that might be unexpected from knowledge of their constituent parts. They can be described theoretically using the tools of condensed matter and statistical physics as "living" soft materials. This award supports research to understand the interplay of physical and biochemical mechanisms in controlling the organized collective motion of a large number of swimming micro-organisms, with the goal of shedding light on the biological advantage of self-organization as compared to random swimming. A related project focuses on the behavior of cells that can spontaneously move, on soft substrates or embedded in soft three-dimensional gels, with the goal of understanding the role of the matrix in controlling collective cell migration, organization and sorting, ultimately leading to tissue formation.Members of underrepresented groups and undergraduate students will be actively recruited to participate in this research project.