The Physical Role of Lipopolymers in the Modulation of Interfacial Forces and Dissipative Pattern Formation in Biomembrane Models

Abstract

A new class of model cell membranes which is separated from the solid substrate via linear polymer spacers of defined length was established in order to unravel the physical role of soft polymers attached to the membrane surface (e.g. glycocalyx) in modulating cell-cell interactions. Using specular neutron and X-ray reflectometry as well as ellipsometry the influence of the lateral density and length of the polymer chains on the membrane-substrate interactions was systematically investigated. The combination of different reflectivity techniques at various osmotic pressures and in bulk water enabled the calculation of quantitative force-distance relationships which reveal the interplay of the major interfacial forces determining the equilibrium distance. During the transfer of lipid-lipopolymer monolayers from the air-water interface to solid substrates by vertical lifting, stripe patterns parallel to the transfer direction appear. A deeper insight into the pattern formation process is taken by two uniquely designed experimental setups that allow for the in situ observation of phase separation during film transfer. The dependence of the characteristic length on the preparation parameters was systematically discussed in the theoretical framework of phase separation: In fact, the experimental results at low transfer speeds could be well explained with the Cahn-Hilliard equation.