CAREER: Statistical Mechanics of Cellular Structures

Northeastern University, Boston MA

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports theoretical and computational research integrated with education to gain a unified understanding of the physical properties of cellular materials. From honeycombs to foams to biological cells, materials with cellular structures are ubiquitous in nature. To advance understanding of cellular materials, the PI will use an interdisciplinary approach that combines knowledge and techniques from physics, geometry, and biology. Organ surfaces are covered with dense layers of cells, acting as physical barriers. While normally non-migratory, cells can undergo active rearrangements during basic processes such as embryo development, morphogenesis, repair, and remodeling. In these events, the cell layer transitions from a solid-like state to a fluid-like state. This striking transition is traditionally studied in the context of cells on a flat surface. However, most organ surfaces are naturally non-flat, and comprised of curved surfaces such as spheres, saddles, or cylinders. How surface curvature affects cell motion remains largely unknown. To address these questions, the principal investigator will study how cells move collectively on a curved surface and the role of curvature on whether they behave like a solid or a fluid. These investigations will generate predictions that can be tested experimentally in living embryos and lab-cultured tissues. The knowledge gained from biological tissues will serve as an inspiration for the PI to investigate the origin of rigidity in other cellular structures. These include the meshwork of forces in a solid or a mechanical network constructed by randomly connecting springs. The goal is to develop design principles for cellular structures to exhibit unusual mechanical properties and take advantage of them to design functional materials that do not readily occur in nature. This CAREER award also supports educational activities tightly integrated with the research. The goal is to increase diversity and retention of students taking physics classes for the very first time, whether in high school or college. The PI will collaborate with K-12 STEM educators to design unconventional yet accessible teaching modules for introductory physics classes. The modules will be based on biophysics, epidemiology, and biology while drawing connections to the fundamental physical concepts taught in introductory physics. These modules, which differ greatly from conventional "textbook examples", will provide students an eye-opening experience on the applicability and impact of physics concepts. TECHNICAL SUMMARY This CAREER award supports integrated theoretical and computational research, outreach, and education with the aim to advance the fundamental understanding of the statistical mechanics and collective behavior of cellular materials, including biological tissues, foams, granular packings, and their force networks. In the biological context, the project will investigate the nature of the jamming/unjamming transition in multicellular collectives constrained on a curved surface and elucidate the origin of coherent angular motion that arises as a unique consequence of non-zero Gaussian curvature. In non-biological cellular structures, the PI will investigate the consequence of mechanical dualities. The objective will involve deriving an effective Hamiltonian in the force space for disordered granular solids based on the dual correspondence between self-stress states and floppy modes. The framework will be the basis for exploring the force-network ensemble of disordered grain packings. The PI proposes to leverage the duality of self-stresses and floppy modes to design disordered mechanical metamaterials with phononic bandgaps. This CAREER award also supports educational activities tightly integrated with the research. The goal is to increase diversity and retention of students taking physics classes for the very first time, whether in high school or college. The PI will collaborate with K-12 STEM educators to design unconventional yet accessible teaching modules for introductory physics classes. The modules will be based on biophysics, epidemiology, and biology while drawing connections to the fundamental physical concepts taught in introductory physics. These modules, which differ greatly from conventional "textbook examples", will provide students an eye-opening experience on the applicability and impact of physics concepts. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.