Multiscale Structural Dynamics of Unilamellar Liposomes in Polymeric Viscoelastic Medium: From Bulk to Micro Environment

The dynamic interactions between membrane lipids and extracellular matrix in macromolecularly crowded mediums affect the properties of the membrane. In the present study, we used 100-nm unilamellar DMPC/DMPG liposomes, and Polyethylene Glycol (PEG) with various molecular weights, from 1.5 to 400 kDa, to explore the effects of length of the polymer chains on structural dynamics of the membranes from bulk to micro environment.  Wide angle x-ray scattering analysis revealed that PEG chains are attached to bilayer surface due to the attractive interactions without causing a notable structural change. Rheology of the solutions shows that adsorbed PEG layers increase the bulk viscosity of membranes and cause a stiffening behavior with monotonically decreasing diffusion constants as M_w increases. According to the microviscosity measurements by fluorescence lifetime spectroscopy (FLS), the presence of PEG decreases the microviscosity in all molecular weights, and the bulk viscosity dominates the lipid bilayer dynamics. This study shows that the dynamics of the membranes can be effectively controlled by changing the length and size of the attached polymer, which can be useful for targeted drug delivery systems.