Fiber networks amplify active stress
Living organisms generate forces to move, change shape and maintain their internal functions. These forces are typically produced by molecular motors embedded in networks of fibers. While these motors are traditionally regarded as the defining elements of biological force generation, we have shown recently that the surrounding network also plays a central role in this process. Indeed, rather than merely propagating forces like a simple elastic medium, fiber networks produce emergent, dramatically amplified stresses, and can go so far as reversing small-scale extensile forces into large-scale contraction. Our theory quantitatively accounts for experimental measurements of contraction, and suggests mechanisms for the physiological regulation of biological active stresses.