Local deformation fields in active soft matter induced by internal stresses*

In many active soft materials, force generation, storage, and dissipation occur across length and time scales. This multiscale interaction between active force generating units and dissipative structural units is the defining character of active materials. Understanding how deformations induced by internal stresses propagate across these materials can provide insights into the underpinning mechanisms of this behavior. Here we present a method to measure such deformation fields. Specifically we use microscopy images to investigate systems driven by transient internal active stresses. We illustrate the application of this method in various actomyosin networks. 

We first start by showing how active stresses propagate in a 2d liquid crystal formed by short actin filaments. We then show how deformation fields in disordered actin networks change with network viscoelasticity. Finally, we measure the local strain fields of stress fibers in single cells, which are induced by myosin mini-filaments and F-actin retrograde flow. The convoluted feedback loops in the cells can be better understood by performing these measurements while perturbing multiple controlling pathways of the actomyosin cytoskeleton, including those that alter the active stresses and the viscoelasticity of the network.