[SMaLS] Non-equilibrium fluctuations of active membrane-like structure

Speaker: Qi Zhang (Postdoc Dogic Lab)

Title: Non-equilibrium fluctuations of active membrane-like structure

Abstract: Recently, increasing attention has been devoted to understanding how
activity—internally generated energy input—affects soft matter systems, including
liquid crystals and dense phases. Beyond these bulk states, interfaces and membranes
play essential roles in organizing dynamics; however, active membranes remain far less
explored. A prominent example is the cell membrane, yet its complexity obscures the
underlying physical mechanisms. To address this challenge, we study a reconstituted
cytoskeletal system composed of microtubules and kinesin-4 motors. We show that tip-
accumulating kinesin-4 drives the formation of macroscopic, one-filament-thick
monolayer membranes. These membranes exhibit large, continuous height fluctuations,
but local protrusions do not grow indefinitely. Instead, once a critical amplitude is
reached, they rapidly relax. Combining continuum analysis with single-molecule
measurements, we find that this relaxation is coupled to local disassembly and
subsequent microtubule recruitment. This feedback between active stress and turnover
stabilizes the membrane and regulates its fluctuations, providing a minimal platform for
understanding active membrane mechanics.