Penetration of thin polymeric membranes by microswimmers

At the microscale, particles and microorganisms are often filtered by or swim through thin networks of polymers immersed in a viscous fluid. For instance, ascidians feed by filtering particles through a mucosal interface composed of a discrete mesh of filaments with pores comparable to the size of prey bacteria. Due to the length scales involved, we model this polymeric interface as a discrete elastic network rather than adopting a continuum description. Connectivities and stiffnesses of elastic links between network nodes endow the interface with membrane-like material properties. Network links could also be dynamically broken if, for instance, they experience a stress beyond a given threshold. Here we use a regularized Stokeslet boundary element method to compute the motion of a microswimmer as it attempts to penetrate this interface. We compare the dynamics of both externally-driven spherical particles and helically-propelled microswimmers that are either free-swimmers like natural bacteria or externally-actuated like many microrobots. We found that the ability of a particle or microswimmer to successfully penetrate the membrane depends on the mode of propulsion as well as the network properties.