Modeling strain-induced nematic order in the extra-cellular matrix driven by contractile cells

The extracellular matrix (ECM) is a network of fibrous biopolymer macromolecules that, along with living cells, compose biological tissue, with nonlinear mechanical properties that depend on filament density, orientation, and crosslinking. When cells immersed in the ECM contract, the resulting mechanical strain creates bands of aligned filaments, forming stiff nematic domains that bridge between adjacent cells. We present a coarse-grained simulation of ECM mechanical response, where each filament is modeled as a bead-chain polymer. Network formation is controlled by introducing cross-linking sites on each filament with specified density and maximum link coordination number. We explore the role of network geometry in the onset of nematic order and nonlinear elastic response under applied strain. Filaments aggregate into inter-connected bundles with both hard crosslinks and Y-junctions where bundled filaments can peel apart under strain. We test the hypothesis that an optimized density of Y-junctions promotes onset of nematic order as a function of mechanical strain.