Probing Local Force Propagation in Tensed Fibrous Gels

Abstract

Fibrous hydrogels are a key component of soft animal tissues. They support cellular functions and facilitate efficient mechanical communication between cells. Due to their nonlinear mechanical properties, fibrous materials display non-trivial force propagation at the microscale, that is enhanced compared to that of linear-elastic materials. In the body, tissues are constantly subjected to external loads that tense or compress them, modifying their micro-mechanical properties into an anisotropic state. However, it is unknown how force propagation is modified by this isotropic-to-anisotropic transition. Here, we directly measure force propagation in tensed fibrin hydrogels. Local perturbations are induced by oscillating microspheres using optical tweezers. We use both 1-point and 2-point microrheology to simultaneously measure both the shear modulus and force propagation. We suggest a mathematical framework to quantify anisotropic force propagation trends. We show that force propagation becomes anisotropic in tensed gels, with, surprisingly, stronger response to perturbations perpendicular to the axis of tension. Our results suggest that under external loads, there are favoured directions of mechanical communication between cells in a tissue. Importantly, we also find that external tension increases the range of force transmission by altering the power-law exponent governing the decay of oscillations with distance from the perturbation. We end with a discussion of possible implications and future directions for research.