Abstract

The mechanics of cells and tissues are largely governed by scaffolds of filamentous proteins that make up the cytoskeleton, as well as extracellular matrices. Evidence is emerging that such networks can exhibit rich mechanical phase behavior. A classic example of a mechanical phase transition was identified by Maxwell for macroscopic engineering structures: networks of struts or springs exhibit a continuous, second-order phase transition at the isostatic point, where the number of constraints imposed by connectivity just equals the number of mechanical degrees of freedom. We will present recent theoretical predictions and experimental evidence for mechanical phase transitions in both synthetic and biopolymer networks. Living systems typically operate far from thermodynamic equilibrium, which affects both their dynamics and mechanical response. As a result of enzymatic activity at the molecular scale, living systems characteristically violate detailed balance, a fundamental principle of equilibrium statistical mechanics. We discuss fundamental non-equilibrium signatures of living systems, including violations of detailed balance at the meso-scale of whole cells.

About the speaker

Fred MacKintosh received his PhD in Theoretical Physics from Princeton University. Following a postdoc at Exxon Corporate Research, he joined the Physics Department at the University of Michigan as Assistant, then Associate Professor. In 2001, Fred joined the Vrije Universiteit in Amsterdam as Professor of Theoretical Physics of Complex Systems. Since 2016, he has been the Abercrombie Professor of Chemical and Biomolecular Engineering at Rice University, as well as a member of the Center for Theoretical Biological Physics, with additional appointments in the Departments of Chemistry and Physics and Astronomy. His primary research interests include the physics of biopolymers and their networks, cell mechanics and non-equilibrium aspects of active soft matter.