Dr. Bi focuses on understanding the behavior of soft matter and biological systems using the tools of statistical mechanics and non-equilibrium physics. In particular, he is interested in the emergence of collective behavior in dense biological tissues. Together with collaborators at Harvard School of Public Health, he discovered the unjamming transition in confluent tissue monolayers that are not controlled by density, but instead by single-cell parameters such as cell-cell adhesion, cortical tension, and cell motility. Together they have been applying theoretical ideas and methods to understand jamming and fluidity in human bronchial epithelial cells from the human lung with profound implications for asthmatic disease progression. Recent works have shed light on a unification of the cell shape changes across a large spectrum of tissues that undergo collective cell unjamming and uncovered structural and dynamic signatures of two distinct routes to motility, the Epithelial-Mesenchymal Transition, and the Unjamming transition.