Buckling and Beating of Motile Microtubules in Soft Networks

We embed microtubules in a viscoelastic polymer network with covalently-attached molecular motors. Pushed by the motors, microtubules exhibit ballistic motion in a 3D analogue of a conventional motility assay. When pinned on their forward-moving ends, microtubules can buckle under the axial load. Such instabilities can generate microtubule oscillations in several distinct 3D beating patterns, pushing against the background viscoelastic network. We simultaneously visualize individual microtubules and local perturbations to the background network. Microtubule length, motor activity, background viscoelasticity, and pinning mechanism are easily tuned, revealing the physical mechanism responsible for internally-driven beating. Understanding this mechanism paves the way toward generating dynamical elastic solids driven by internally controlled beating.