Equilibrium and dynamics of PEO/PPO/PEO penetration into DPPC monolayers

The interaction of synthetic polymers with living tissue is of interest in a wide range of biochemical and biomedical applications ranging from cell culture in large-scale bioreactors to pharmaceutic and cosmetic products. To gain insight into the physico-chemical interactions between polymeric material and cell membranes, we study the equilibrium and dynamic penetration of a symmetric triblock copolymer (PEO/PPO/PEO) into DPPC monolayers using a novel coaxial capillary pendant drop technique. A well-defined initial condition of the insoluble monolayer was established by first spreading the lipid onto a water drop formed at the tip of two (concentric) capillaries. The lipid was subsequently compressed to a specified surface state. Afterwards, the droplet subphase was exchanged by injecting a polymer solution from one of the capillaries and withdrawing liquid from the other under a constant total (drop) volume. The effects of polymer concentration and fractional coverage of the lipid monolayer on the surface pressure evolution were investigated. ta suggests that the adsorption of polymer into the lipid monolayer is reversible and that upon compression of the surface, the lipid can eject the macromolecule from the surface. A comparison of the equilibrium surface pressure of the penetrated monolayer with the surface pressure of the polymer alone shows that interactions in the adsorbed layer are non-ideal and consistent with polymer–lipid repulsion. Both desorption of the polymer from a suddenly compressed interface and response to oscillatory perturbation of the interface show that a characteristic timescale in the kinetics of monolayer relaxation is in the order of 100 s. Because of the elevated concentration of polymer in the bulk phase, this suggests a kinetic barrier to macromolecule adsorption/desorption.