Liquid crystal domains and thixotropy of filamentous actin suspensions.

摘要: Abstract The thixotropic properties of filamentous actin suspensions were examined by a step-function shearing protocol. Samples purified sheared at 0.2 sec-1 in cone and plate rheometer. We noted sharp stress overshoot upon the initiation shear, indicative gel state, nearly instantaneous drop to zero cessation shear. Stress-overshoot recovery was almost complete after 5 min "rest" before samples again sec-1. Overshoot increased linearly with square root rest time, suggesting that gel-state is diffusion limited. Actin subjected oscillatory frequencies from 0.003 30 radians/sec confirmed existence 5-min time scale gel, similar for stress-overshoot recovery. Flow visualized polarized light observations. 6 mg/ml 20 showed "polycrystalline" texture birefringence typical liquid crystal structure. At shear rates less than 1 sec-1, flow occurred relative movement irregular, roughly ellipsoidal domains 40-140 microns long; appearance moving ice floes. greater decreased size, possibly frictional interactions among domains. Eventually "river" aligned flow. Our observations confirm our previous domain-friction model rheology. The similarities between unusual cytoplasm argue also may as