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Dr. Bi uses physics and mechanics to study cell motility and collective migration in biological tissues. Cell motion inside dense tissues governs many important processes, including embryonic development and cancer metastasis. Although recent experiments have suggested that these tissues exhibit a jamming transition from a fluid-like to a solid-like state, it remains unclear how cell motility and cell–cell interactions control this transition. Dr. Bi has built a theoretical framework that captures both of these effects, and has discovered that the jamming transition is controlled by single-cell speed, the persistence of single-cell motion, and a mechanical parameter that characterizes the competition between cell–cell adhesion and cortical tension. Working with biologists, he has identified an experimentally accessible structural order parameter—the cell shape index—that specifies the entire transition surface. 

He is also interested in cell rearrangements and tissue remodeling during embryonic development, and in understanding theoretical and numerical models for cancer tumor metastasis.