Stochastic elastohydrodynamics of contact and coarsening during membrane adhesion

Abstract

Contact between fluctuating, fluid-lubricated soft surfaces is prevalent in engineering and biological systems, a process starting with adhesive contact, which can give rise to complex coarsening dynamics. One representation of such a system, which is relevant to biological membrane adhesion, is a fluctuating elastic interface covered by adhesive molecules that bind and unbind to a solid substrate across a narrow gap filled with a viscous fluid. This flow is described by the stochastic elastohydrodynamics thin-film equation, which combines the effects of viscous nanometric thin film flow, elastic membrane properties, adhesive springs, and thermal fluctuations. The average time it takes the fluctuating elastic membrane to adhere is predicted by the rare event theory, increasing exponentially with the square of the initial gap height. Numerical simulations reveal a phase separation of membrane domains driven by the binding and unbinding of adhesive molecules. The coarsening process displays close similarities to classical Ostwald ripening; however, the inclusion of hydrodynamics affects power-law growth. In particular, we identify a new bending-dominated coarsening regime, which is slower than the well-known tension-dominated case.