Surface energy of phospholipid bilayers and the correlation to their hydration.

Supported lipid bilayers (SLBs) were prepared on glass and silicon slides grafted with polyethylene glycol (PEG) and covalently bound cholesteryl anchors to fix the lipid bilayer on the surface. Phospholipid bilayers and bilayers modified by addition of covalently bound PEG were investigated. Using contact angle measurements, the surface energy components of bilayer surfaces were analyzed using van Oss' and Owens-Wendt's methods. A quantitative correlation between the polar proton acceptor component of the surface energies and the respective hydration densities was proven for SLBs of pure lipids. We could show that the presence of PEG in the SLB produces a significant change of the proton acceptor component. Regarding the correlation between the surface energies and the hydration densities of SLBs with PEG, we were able to show a dependency on the PEG conformation.