Rheology and Microrheology of Semiflexible Polymer Solutions: Actin Filament Networks

Abstract

We report a systematic study of the linear rheology of solutions of model semiflexible polymers, actin filaments (F-actin), using mechanical rheometry, diffusing wave spectroscopy (DWS), and video-based single-particle tracking microrheology. For pure actin at c = 24 μM and after full polymerization, the elastic and loss moduli still increase with time as G‘(t) ∝ t0.25±0.02 and G‘‘(t) ∝ t0.15±0.03, when measured at 1 rad/s, during network formation and reach a plateau after 12 h. At equilibrium, the linear small-frequency elastic modulus has a small magnitude, G‘p = 14 ± 3 dynes/cm2. The magnitude of G‘p depends weakly on concentration as G‘p(c) ∝ c1.2±0.2, with an exponent much smaller than for flexible polymers. At large concentrations, F-actin network becomes a liquid crystal and G‘p is independent of concentration. Using the large bandwidth of DWS, we show that the high-frequency viscoelastic modulus of F-actin solutions varies with the shear frequency as |G*(ω)| ∝ ω0.78±0.10 for both the isotropic ph...