Strain-enhanced stress relaxation impacts nonlinear elasticity in collagen gels

Significance The extracellular matrix is a complex assembly of structural proteins that provides physical support and biochemical signaling to cells within our tissues. One of the key structural components of the extracellular matrix is collagen, and matrices of collagen exhibit remarkable mechanical properties. Their resistance to deformation is enhanced as deformation is increased over short timescales, a behavior termed strain stiffening, yet they exhibit some characteristics of viscous fluids at longer timescales. Strikingly, we show that the strain stiffening of collagen matrices is coupled with their liquid-like behavior: at greater deformations, these matrices become stiffer but then flow more rapidly to relax this increase in stiffness. These complex mechanical behaviors are likely to be relevant to cellular interactions with these matrices.