Physical properties of single cells and collective behavior

Cells display a high degree of functional organization, largely attributed to the intracellular biopolymer scaffold known as the cytoskeleton. This inherently complex structure drives the system out of equilibrium by constantly consuming energy to conserve or reorganize its structure. Thus, the active, structurally organized cytoskeleton is the key player for the emergent mechanical properties of cells, which further determine properties of cell clusters and even multicellular organisms. In this spirit, this chapter introduces the physical principles on the different levels of biological complexity ranging from single biopolymers to tissues. The emergent mechanical properties and their respective effects on each level will be highlighted with a strong emphasis on their intertwined nature.