Triggering salt-induced contraction of cytoskeletal networks with microfluidics*

The mechanical tunability and morphology of the cytoskeleton is determined by interacting networks of semiflexible actin filaments and rigid microtubules. By altering the chemical environment of the cytoskeleton, actin and microtubule networks can dynamically change and rearrange to form entanglements, crosslinks and bundles. For example, increasing the concentration of divalent salt can induce crosslinking and bundling of actin filaments. Here, we use microfluidics and confocal fluorescence microscopy to show that increasing salt concentration triggers contraction of cytoskeleton networks in the absence of motor proteins. Specifically, we use microfluidics to cyclically vary the salt concentration over the course of minutes to hours while simultaneously visualizing the triggered structural changes to the networks and measuring the contraction velocity. Our measurements shed new light on how varying environmental conditions can dynamically tune the morphology of actin-microtubule networks and trigger active contraction without motor proteins.