The viscoelastic response of living cells is determined by heterogenous networks of crosslinked and bundled actin filaments. The quantitative impact of such local network heterogeneities is studied best in well-defined in vitro model systems by employing microscopic and micromechanical techniques. In this study, we show that reconstituted ?-actinin/actin networks exhibit a structural polymorphism, which is dictated by two types of mesoscopic heterogeneities. We investigate the correlation of these two heterogeneities to distinct ?- actinin concentration regimes and demonstrate their influence on the mechanical properties of cross-linked and bundled actin networks. First, locally embedding stiff bundles into the network strengthens the macroscopic network response. Second, the formation of star-like bundle clusters drastically concentrates material in localized spots and weakens the network elasticity. Such bundle cluster networks exhibit kinetically trapped and thus meta-stable network configurations ? which is contrary to the commonly accepted belief of equilibrated network formations.     «

The viscoelastic response of living cells is determined by heterogenous networks of crosslinked and bundled actin filaments. The quantitative impact of such local network heterogeneities is studied best in well-defined in vitro model systems by employing microscopic and micromechanical techniques. In this study, we show that reconstituted ?-actinin/actin networks exhibit a structural polymorphism, which is dictated by two types of mesoscopic heterogeneities. We investigate the correlation of the...     »