Self-organization of dense active matter

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TECHNICAL SUMMARYThe Division of Molecular and Cellular Biosciences and the Division of Materials Research contribute funds to this award. It supports theoretical research and education in active matter. Active matter is composed of many interacting self-driven units, active particles, that individually consume energy and collectively generate motion or mechanical stress. Realizations range from bacterial swarms to epithelial cell colonies to suspensions of artificial colloidal swimmers. The PI will build on her expertise and track record at the interface of soft matter and nonequilibrium statistical physics to investigate three classes of systems:* Bacterial suspensions as model active systems that can self-organize in fluid and solid-like phases, as well as a rich variety of emergent patterns. Using bacterial suspension as prototype systems, the PI will classify the self-sustained dynamical phases of active matter and elucidate their properties. * Self-propelled colloids - Ingenious synthetic analogues of living systems have been engineered that consist of colloidal particles propelled by self-catalytic reactions. These systems provide an ideal quantitative testing ground for active matter theories.* Cell colonies and tissues, with the goal to understand the interplay of cell-cell and cell-extracellular matrix interactions in controlling force generation and transmission, collective migration, and the emergence of the materials properties of living tissues. This project will have a broad, potentially transformative impact across several fields, from physics to biology and biomedical, chemical and tissue engineering. The collaboration with experimental groups will provide focus to the theoretical research on phenomena of direct interest and relevance in this rapidly growing field. The research supported by this award will include opportunities for undergraduates, graduate students and postdoctoral researchers. Its highly interdisciplinary nature will provide broad training at the interface between science and bioengineering, opening up a broad spectrum of employment opportunities.NONTECHNICAL SUMMARYThe Division of Molecular and Cellular Biosciences and the Division of Materials Research contribute funds to this award. It supports theoretical research and education in active matter. The name "active matter" refers to a class of nonequilibrium systems composed of many interacting units or particles that individually consume energy and collectively generate coherent motion at large scales. An example is a suspension of swimming bacteria. Each individual bacterium is an active particle that propels itself through a fluid or other medium by consuming nutrients. A dense swarm of bacteria behaves collectively as a living fluid and can self-organize in complex regular patterns, exhibit turbulent motion, or "freeze" into a solid-like biofilm. This type of "emergent behavior", where a collection of many interacting entities shows large-scale spatial or temporal organization in a state with novel macroscopic properties, occurs of course also in inanimate matter (for instance, the transition from water to ice as one lowers the temperature), but acquires a new unexplored richness in active systems that are tuned not by an external knob (the temperature), but by energy generated internally by each unit. Active systems span an enormous range of length scales, from the cytoskeleton of living cells, to bacterial suspensions, tissues and organisms, to animal groups such as bird flocks, fish schools and insect swarms. The ability to turn energy injected at the molecular scale into organized and complex motion and specific functions at the macroscopic scale is a unique mechanical property of the living state. The research supported by this award aims at understanding and harnessing this defining property by answering several questions: Are there "universal" properties in the behavior of living matter, such as the "freezing" of a dense bacterial swarm into a solid-like biofilm or the glassy dynamics of confluent cell layers, that can be described using the tools and ideas of condensed matter physics? Can some of the defining properties of living systems, such as motility or the ability to adapt their response to external stimuli, be reproduced in synthetic constructs? How does the emergent behavior of tissues, such as their mechanical properties, arise from that of individual cells?The project will have a broad, potentially transformative impact across several fields, from physics to biology and biomedical, chemical and tissue engineering, and benefit society in several ways. For instance, understanding collective behavior of cells during wound healing and biofilm formation will aid in the characterization of how alterations and mutations in individual cells affect collective mechanical properties and may lead to pathologies. The research supported by this award will include opportunities for undergraduates, graduate students and postdoctoral researchers. Its highly interdisciplinary nature will provide broad training at the interface between science and bioengineering, opening up a broad spectrum of employment opportunities.