(608e) Effects of Crowding on the Diffusivity of Membrane Adhered Particles

receptors, drives critical biological processes, including the formation of complexes, cell-cell signaling,

and membrane trafficking. These diffusive processes are complicated by how concentrated,

or “crowded”, the inclusions are, which can occupy between 30-50% of the area fraction of the

membrane. In this work, we elucidate the effects of increasing concentration of model membrane

inclusions in a free-standing artificial cell membrane on inclusion diffusivity and the apparent viscosity

of the membrane. By multiple particle tracking of fluorescent nanoparticles covalently tethered to

the bilayer, we show the transition from expected Brownian dynamics, which accurately measure

the membrane viscosity, to subdiffusive behavior with decreased diffusion coefficient as the particle

area fraction increases from 1% to around 30%, approaching physiological levels of crowding. Using

hydrodynamic models relating the 2D diffusion coefficient to the viscosity of a membrane, we

determine the apparent viscosity of the bilayer from the particle diffusivity and show an increase in

the apparent membrane viscosity with increasing particle area fraction, however, the scaling of this

increase is in contrast with the behavior of monolayer inclusion diffusion and bulks suspension rheology.

These results demonstrate that physiological levels of model membrane crowding nontrivially

alter the dynamics and apparent viscosity of the system, which has implications for understanding

membrane protein interactions and nanoparticle-membrane transport processes.