Characterization of a Biomimetic Polymeric Lipid Bilayer by Phase Sensitive Neutron Reflectometry

Neutron reflectivity measurements were performed on a cell membrane mimic system consisting of a polyelectrolyte multilayer plus a synthetic terpolymer plus a phospholipid layer, at all of the intermediate steps in the assembly of the composite, to obtain neutron scattering length density depth profiles. The polyelectrolyte multilayer functions as a soft, water-containing cushion for the membrane mimic, formed by the synthetic terpolymer and the phospholipid layer. The systems were studied dry, in 92% humidity and wet, or fully hydrated, using a phase-sensitive neutron reflectometry technique. By using two water conditions (D2O and H2O mixtures) on the polyelectrolyte multilayer plus terpolymer plus phospholipid layer assembly, the distribution of water in the layers was obtained. It was found that the supported membrane-mimic has 40% water content in the “cushion” polyelectrolyte multilayer under humid conditions. Under the same conditions, a 10% water content was found in the terpolymer-phospholipid region. The overall thickness change due to the water uptake under these conditions was found to be 10 Å and was due to an increase in thickness of the polyelectrolyte multilayers. Because fusing phospholipid vesicles onto the polyelectrolyte multilayer plus synthetic terpolymer assembly shows the appearance of a 20 Å increase in thickness of the composite film system, it can be inferred that a phospholipid monolayer was formed. In addition, the terpolymer layer undergoes significant rearrangement upon the addition of the