Probing membrane material properties with complex and dynamic fluid environments*

Membranes are composed of a variety of materials whose distribution, in combination with enclosed volume, can result in distinct and functional morphologies. It is of generic biological interest and importance to measure these material properties and many methods are used; a red blood cell's bending stiffness, for instance, may been measured by stretching it in a delicate process requiring optical tweezers. We will discuss a few new methods for probing membrane material properties like bending stiffness and spontaneous curvature using complex fluid environments, namely liquid crystals, and using fluid flows. By placing red blood cells into a liquid crystalline environment we show that the sharing of strain between the fluid and the cells can be used to rapidly characterize multiple cells in a population, and perhaps to detect problematic variants. Patches of distinct material properties along the surface, meanwhile, presents new measurement challenges, but new developments on multicomponent cell behavior in flows can also be used to infer membrane composition. Although a richness of shapes and behaviors emerge, we provide physical intuition for the roles of material properties on deformation and dynamics in both contexts.