[SY-H2] Controlling the mechanics of a synthetic hydrogel with motor-like internal contractility
Stiffening due to internal stress generation is common in living materials and regulates many biomechanical processes. For example, cells stiffen their surrounding matrix by pulling on collagen and fibrin fibers. At the subcellular level, molecular motors prompt fluidisation and stiffening of the cytoskeleton by sliding polar actin filaments in opposite directions. I will present results showing that synthetic materials, likewise, are able to change their stiffness in response to internally generated and externally applied forces. Theoretical and experimental results are presented for a system where chemical crosslinking of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) into a fibrous matrix of synthetic semi-flexible polymers allows for internal stress generation upon induction of coil-to-globule transition, resulting in a macroscopic stiffening response spanning up to three orders of magnitude. Strikingly, the forces generated by PNIPAM collapse are sufficient to drive a fluid material into a stiff gel within a few minutes. Rigidified networks dramatically stiffen in response to applied stress featuring power law rheology with exponents that match those of reconstituted actomyosin networks pre-stressed by molecular motors. This concept holds potential for the rational design of responsive synthetic materials that are fluid at room temperature and rapidly rigidify at body temperature to form hydrogels mechanically compatible to cells or tissues.