The cytoskeleton is a network of crosslinked, semiflexible filaments, and it has been suggested that it has properties of a glassy state. Here we employ optical-trap-based microrheology to apply forces to a model cytoskeleton and measure the high-bandwidth response at an anterior point. Simulating the highly nonlinear and anisotropic stress-strain propagation assuming affinity, we found that theoretical predictions for the quasistatic response of semiflexible polymers are only realized at high frequencies inaccessible to conventional rheometers. We give a theoretical basis for determining the frequency when both affinity and quasistaticity are valid, and we discuss with experimental evidence that the relaxations at lower frequencies can be characterized by the experimentally obtained nonaffinity parameter.

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The mechanics of cells or cytoskeletons have been understood either as a network of semi-flexible polymers or a glass. Here we employ optical-trap based microrheology to apply forces to cytoskeleton and measure the highbandwidth response at an anterior point. Simulating the highly nonlinear and anisotropic stress-strain propagation assuming affinity, we found that theoretical predictions for the quasi-static response are only realized at high frequencies inaccessible to conventional rheometers. We give a theoretical basis for determining the critical frequency when both affinity and quasistaticity are valid, and discuss with experimental evidence that the relaxations at lower frequencies can be characterized by the experimentally obtained non-affinity parameter.