5 research outputs found
Solid friction between soft filaments
Any macroscopic deformation of a filamentous bundle is necessarily
accompanied by local sliding and/or stretching of the constituent filaments.
Yet the nature of the sliding friction between two aligned filaments
interacting through multiple contacts remains largely unexplored. Here, by
directly measuring the sliding forces between two bundled F-actin filaments, we
show that these frictional forces are unexpectedly large, scale logarithmically
with sliding velocity as in solid-like friction, and exhibit complex dependence
on the filaments' overlap length. We also show that a reduction of the
frictional force by orders of magnitude, associated with a transition from
solid-like friction to Stokes' drag, can be induced by coating F-actin with
polymeric brushes. Furthermore, we observe similar transitions in filamentous
microtubules and bacterial flagella. Our findings demonstrate how altering a
filament's elasticity, structure and interactions can be used to engineer
interfilament friction and thus tune the properties of fibrous composite
materials
Microtubules soften due to cross-sectional flattening.
We use optical trapping to continuously bend an isolated microtubule while simultaneously measuring the applied force and the resulting filament strain, thus allowing us to determine its elastic properties over a wide range of applied strains. We find that, while in the low-strain regime, microtubules may be quantitatively described in terms of the classical Euler-Bernoulli elastic filament, above a critical strain they deviate from this simple elastic model, showing a softening response with increasingdeformations. A three-dimensional thin-shell model, in which the increased mechanical compliance is caused by flattening and eventual buckling of the filament cross-section, captures this softening effect in the high strain regime and yields quantitative values of the effective mechanical properties of microtubules. Our results demonstrate that properties of microtubules are highly dependent on the magnitude of the applied strain and offer a new interpretation for the large variety in microtubule mechanical data measured by different methods