Biological tissues are often framed simply as fluids or solids, creating a binary that overlooks rich intermediate structures. In this talk, I present two theoretical advances revealing how tissues utilize activity and mechanics to access exotic geometric orders. First, I discuss the emergence of the hexatic phase—orientational order without translational order. We show that cell division, typically a disordering force, drives hexatic order when coupled with motility. This occurs via a "defect healing" mechanism where motility actively binds disclinations into dislocations. Second, I examine hyperuniformity—a hidden global order suppressing density fluctuations. We demonstrate that hyperuniformity exists across a spectrum of tissue states, distinct from mechanical rigidity, and introduce the "Hyperuniform Poisson Ensemble" (HyPE) as a thermodynamic lower bound. These findings highlight how tissues decouple rigidity from structure, offering blueprints for active metamaterials.
Dapeng "Max" Bi is an Associate Professor of Physics at Northeastern University. He earned his Ph.D. from Brandeis University in 2012 and completed postdoctoral research at Syracuse and Rockefeller Universities. His work has been recognized with the NSF CAREER Award, the Sloan Research Fellowship, and the NIH MIRA. Dr. Bi uses physics to study how biological tissues and other soft materials behave, looking at how cells move and organize in systems ranging from embryos and tumors to granular matter.
Max Bi, Assistant Professor, Northeastern University
Host: Michelle Driscoll
Joan West
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