Targeting Mechanical Hysteresis of Actin Networks using Bio-Synthetic Crosslinkers

Rheological studies of in vitro actin networks provide critical insights into cell mechanics and provide design inspiration for new materials. Actin networks are dynamic and flexible yet can resist deformation through strain-stiffening. Recent studies have shown that that the magnitude of stiffening, or differential modulus, K, of actin networks is directionally increased through the application of a pre-stress that aligns the actin filaments. Computational simulations hypothesized that this mechanical hysteresis is dependent on crosslinker length, flexibility, and binding kinetics. Current in vitro actin network studies rely on proteinaceous crosslinkers that are difficult to engineer to rigorously study the mechanical impacts of crosslinker variables. In this study, we probe the mechanical hysteresis of actin networks using bio-synthetic crosslinkers comprised of polyethylene glycol (PEG) polymers end functionalized with actin binding peptides. These peptide-PEG constructs allow for finer control over crosslinker variables. Using bulk rheology, we demonstrate the effectiveness of these bio-synthetic crosslinkers in generating strain-stiffening actin networks and investigate the resulting mechanical hysteresis as a function of PEG molecular weight and relative crosslinker concentration. The results from these studies provide greater insight into cell cortex mechanics as well as a roadmap for the generation of new synthetic materials with tunable strain-stiffening properties.