(647i) Aggregation Mechanism and Stability of Clustered Structures in Viscous Membranes

Eukaryotic cell membranes are a crowded assembly of molecular motors, ion pumps, and other biomolecular machines embedded in the bilayer matrix. Biomimetic membranes made of polymer assemblies also display similar properties, and are promising candidates for drug delivery applications. We investigate the collective behavior of active inclusions in confined membranes - viscous membranes adjacent to a shallow subphase.

We develop a computational framework using a point-particle approach where hydrodynamic interactions within the membrane are captured by accurate long-range Green’s functions. We simulate particles for fixed Saffman-Delbrück length (the ratio of the membrane and subphase viscosities) and a range of confinement strengths. The simulations reveal a systematic transition in clustering from oriented string-like aggregates to hexatic arrangements upon an increase in the confinement strength. We quantify this transition using pair distribution functions and moments of the cluster size distribution.

Using theory and simulations, we then examine the linear stability of string-like oriented structures and the long-term stability of hexatic clusters as a function of confinement strengths. These results provide an explanation for the transition in the clustering mechanism. Lastly, we also incorporate appropriate Brownian noise in the system to study the affects of thermal fluctuations, where the effects observed without any Brownian noise still persist. Taken together, this work could explain the hydrodynamic mechanisms behind the ordering and structuring of active inclusions in certain physiological conditions, and provide insight into possibly tuning the behavior of such inclusions.