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  • Internal friction controls active ciliary oscillations near the instability threshold.

Internal friction controls active ciliary oscillations near the instability threshold.

Science advances (2020-08-28)
Debasmita Mondal, Ronojoy Adhikari, Prerna Sharma
ABSTRACT

Ciliary oscillations driven by molecular motors cause fluid motion at micron scale. Stable oscillations require a substantial source of dissipation to balance the energy input of motors. Conventionally, it stems from external fluid. We show, in contrast, that external fluid friction is negligible compared to internal elastic stress through a simultaneous measurement of motion and flow field of an isolated and active Chlamydomonas cilium beating near the instability threshold. Consequently, internal friction emerges as the sole source of dissipation for ciliary oscillations. We combine these experimental insights with theoretical modeling of active filaments to show that an instability to oscillations takes place when active stresses are strain softening and shear thinning. Together, our results reveal a counterintuitive mechanism of ciliary beating and provide a general experimental and theoretical methodology to analyze other active filaments, both biological and synthetic ones.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
1,2-Dilinoleoyl-3-palmitoyl-rac-glycerol, ≥95% (TLC), liquid
Sigma-Aldrich
IGEPAL® CA-630, for molecular biology
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Poly-L-lysine hydrobromide, mol wt 15,000-30,000 by viscosity
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Creatine Phosphokinase from bovine heart, Type III, salt-free, lyophilized powder, ≥30 units/mg protein
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Sodium creatine phosphate dibasic tetrahydrate, ≥98.0% (NT)