Forces at the scale of the cell
The importance of molecular-scale forces in sculpting biological form and function has been acknowledged for more than a century. Accounting for forces in biology is a problem that lies at the intersection of soft condensed matter physics, statistical mechanics, and experimental methods, all adapted to a cellular context. This review surveys how forces arise within the cell. We provide a summary of the relevant background in cell biophysics, of soft-matter systems in and out of thermodynamic equilibrium, and of various force measurement methods. These ideas are then deployed to describe how forces are generated, transmitted, and sensed in specific cell-scale processes. We emphasize active matter descriptions, methodological tools that provide ways of incorporating non-equilibrium effects in a systematic manner into conceptual as well as quantitative descriptions. Our examples include polymerization forces, the motion of molecular motors, the properties of the actomyosin cortex, the mechanics of cell division, and shape changes in tissues. We suggest that a deeper understanding of cell function will necessarily require integrating the action of cell-scale physical forces with the assimilation and processing of information.