| Abstract | The growth and metastasis of tumors are increasingly recognized to be an inherently collective, multiscale problem, wherein understanding at the genetic and molecular level is necessary but is not sufficient; the mechanical response of cells must also be accounted for to understand collective behavior in cancer. Like glassy, granular, and colloidal materials, cells exist in a fundamentally crowded and disordered environment and are capable of undergoing collective phase transitions between states resembling the material phases of solid, liquid, and gas. By mapping concepts from material science to cell motion, it becomes possible to better predict and understand how macroscopic properties of the cellular system – fluidity and rigidity – emerge from physical cellular-scale interactions. These cellular interactions, though enormously complex and variable from a biological standpoint, can be abstracted to generalized state variables, including density, cell shape constraints, and fluctuations, which allow phase diagrams to be constructed to aid in predicting behavior. In this chapter, we review both experimental evidence and theoretical frameworks toward understanding multicellular collectives as material systems, exploring both the power and the limitations of comparisons between biological and non-living soft matter systems. We conclude with how these lessons are being applied to develop a more holistic understanding of how physical constraints affect collective migration and invasion in cancer. |
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