CAREER: Dynamics and Pattern Formation in Active Fluids

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Technical SummaryThis award supports theoretical research, education, and outreach activities at the interface of soft matter and biology. The goal of this research program is to develop quantitative theories for emergent behavior in active fluids. Active fluids are a collection of "particles" that is driven out of equilibrium due to the internal activity of each particle. They differ from traditional nonequilibrium fluid systems because the energy that maintains the system far from equilibrium is generated at the scale of the individual units rather than at a boundary. Particular realizations of active fluids include bacteria in suspension, motile cells on substrates, in vitro systems made of cytoskeletal filaments and motor proteins and catalytically propelled nanorods. The study of these systems has implications for phenomena ranging from cytoskeletal dynamics, bacterial biofilm formation, wound healing, and morphogenesis.Emergent behavior arises in active fluids from a complex interplay between nonequilibrium dynamics arising from physical interactions and bio-chemical regulation that controls the physical properties of the system. Active fluids lack the scale separation between the microscopic dynamics and the observed macroscopic dynamics exhibited in classical fluids, in both space and time. As a consequence, detailed considerations of the effect of boundaries, fluctuations and correlations become critical for building quantitative theories of real systems. This project will address these challenges in two ways: (1) Minimal models, both macroscopic and microscopic, will be studied to unambiguously identify physical mechanisms that lead to observed emergent dynamics and pattern formation in active fluids. (2) Theory will be developed to quantitatively capture the effect of boundaries and fluctuations on the dynamics of out-of-equilibrium systems and applied in research thrusts. Specific planned investigations include: a) Elucidating the influence of collective motility and physical interactions on pattern formation and emergent dynamics; this is relevant at the scale of cytoskeletal dynamics and for collective motility of cells that occurs in wound healing and tissue development. b) Characterizing the role of shape and variable motility in the large scale behavior of these systems with an eye toward bacterial biofilms that are typically made of different phenotypes that show variability in both properties. c) Charting the influence of hard walls on the collective dynamics of motile particles due to both hydrodynamic interactions and direct contact interactions which is relevant for most experimental realizations of active fluids.This award also supports an outreach effort that capitalizes on the accessibility of soft materials physics and its relationship to biological systems through everyday materials and table top demonstrations. Specific initiatives include: a) a multiple contributor website that will be a repository of popular articles on soft materials physics and a teacher's resource center, b) a lecture-demonstration that will introduce the concepts of rheology and its relevance to technological applications and biology targeted at middle school and high school students, and c) a collaborative teacher development program for high school teachers in the Waltham area and the physics faculty at Brandeis to interactively develop aids and innovations to teach science in the class room.Nontechnical Summary:This award supports theoretical research, education, and outreach activities at the interface of soft matter and biology. The cytoskeleton of a living cell is made of long string-like molecules that are interconnected in various places rather like a very tiny poorly made fish net. Viewed this way, it is a material analogous to everyday rubber. Swimming bacteria in a fluid suspension resemble the liquid crystals that form the basis of modern display technology. The key features of these systems, organized under the term active materials, is that they are pushed out of the balance of equilibrium by various biochemical processes that together serve to dynamically remodel the material. This project will use the tools of materials theory to understand complex biological systems such as the examples above in order to understand common mechanisms that underlie observed phenomena in diverse systems. Such a study when coupled to detailed biological and biochemical chemical investigations being undertaken today will serve as a stepping stone towards approaching a quantitative and predictive understanding of biological phenomena ranging from wound healing and morphogenesis to bacterial biofilm formation. This award also supports an outreach effort that capitalizes on the accessibility of soft materials physics and its relationship to biological systems through everyday materials and table top demonstrations. Specific initiatives include: a) a multiple contributor website that will be a repository of popular articles on soft materials physics and a teacher's resource center, b) a lecture-demonstration that will introduce the concepts of rheology and its relevance to technological applications and biology targeted at middle school and high school students, and c) a collaborative teacher development program for high school teachers in the Waltham area and the physics faculty at Brandeis to interactively develop aids and innovations to teach science in the class room.