# Cells exploit a phase transition to mechanically remodel the fibrous extracellular matrix

## TL;DR

This paper reveals that cells mechanically remodel the extracellular matrix through a densification phase transition caused by fiber buckling, which explains the formation of tethers and their role in cell migration and invasion.

## Contribution

It uncovers that tether formation results from a phase transition driven by fiber buckling, combining modeling, simulation, and experiments to explain this biological phenomenon.

## Key findings

- Tether formation is a densification phase transition of the ECM.
- Simulations predict strain discontinuities localized in tethers.
- Experimental active particles mimic cell-induced patterns.

## Abstract

Through mechanical forces, biological cells remodel the surrounding collagen network, generating striking deformation patterns. Tethers-tracts of high densification and fiber alignment-form between cells, thinner bands emanate from cell clusters. While tethers facilitate cell migration and communication, how they form is unclear. Combining modeling, simulation and experiment, we show that tether formation is a densification phase transition of the extracellular matrix, caused by buckling instability of network fibers under cell-induced compression, featuring unexpected similarities with martensitic microstructures. Multiscale averaging yields a two-phase, bistable continuum energy landscape for fibrous collagen, with a densified/aligned second phase. Simulations predict strain discontinuities between the undensified and densified phase, which localizes within tethers as experimentally observed. In our experiments, active particles induce similar localized patterns as cells. This shows how cells exploit an instability to mechanically remodel the extracellular matrix simply by contracting, thereby facilitating mechanosensing, invasion and metastasis.