The mechanical properties of hydrated intermediate filaments: Insights from hagfish slime threads

ABSTRACT Intermediate filaments (IFs) impart mechanical integrity to cells, yet IF mechanics are poorly understood. It is assumed that IFs in cells are as stiff as hard [alpha]-keratin, F-actin, and microtubules, but the high bending flexibility of IFs and the low stiffness of soft [alpha]-keratins suggest that hydrated IFs may be quite soft. To test this hypothesis, we measured the tensile mechanics of the keratin-like threads from hagfish slime, which are an ideal model for exploring the mechanics of IF bundles and IFs because they consist of tightly packed and aligned IFs. Tensile tests suggest that hydrated IF bundles possess low initial stiffness (E^sub i^ = 6.4 MPa) and remarkable …