Single-molecule imaging of tube nonlinearities for sheared, entangled F-actin chains

A homebuilt setup for single-molecule epifluorescence imaging under controlled rheological shear is used to accomplish single-molecule imaging of entangled F-actin solutions. We find “tube softening” at low shear rate and “tube hardening” at high shear rate. Surprisingly, “tube softening” and “tube hardening” are quantitatively related to chain alignment and chain stretching, respectively – quantities that are inaccessible using conventional ensemble-averaged methods.