Cells move in tissue in several situations such as the spread of cancer. It is known that cell motility leads to deformation of the tissue. We argue here that the deformations are generically plastic and irreversible. We study an experimental model system of breast cancer cells in collagen-I. We observe large, irreversible deformations, namely dense collagen bundles between cells which do not decay when the cells stop contracting. We give a numerical model that shows how sliding of cross-links in the collagen can give the observed results. The same model reproduces bulk rheology observations of plasticity. We also observe the micro-rheology of the collagen bundles.

We discuss the implications of our results for cell motility via durotaxis and contact guidance. We propose that cell motility, even at low densities, is a collective effect due to mechanical
communication between cells.
Speaker(s): Leonard Sander (University of Michigan)