Material approaches to active tissue mechanics

Communities of epithelial cells communicate through intercellular interactions, allowing them to coordinate their motility, which plays a key role in homeostasis, morphogenesis and cancer metastasis. Each cell in the epithelium is a constitutive energy-consuming agent, which can generate forces and interact with other cells through cell-cell junctions. Forces applied through external stimuli or endogenous cellular events are balanced by the cells within the epithelium, resulting in the adjustment of internal tissue contractile stresses and tissue reorganization. Materials science and microengineering techniques can be combined to create controllable environments to study epithelial movement and mechanics. By modulating the cell-material interface and by applying principles of active matter, key aspects of epithelial dynamics and mechanosensing mechanisms can be investigated. In this Review, we discuss epithelial tissues as active materials with particular rheological properties and active behaviours at different length scales. We highlight 2D and 3D materials for the study of epithelial dynamics and summarize key methods for the probing of epithelial mechanics. Tissue responses to mechanical stimuli are examined from the molecular level to the tissue level, and the effects of the shape, architecture and stiffness of the microenvironment are discussed.