Phase sensitive neutron reflectometry describes the structure of a membrane-mimetic biomaterial.

Scientists at the NIST Center for Neutron Research (NCNR) and the Department of Surgery at Emory University in Atlanta, GA, are using phase-sensitive neutron reflectometry to characterize the structure of a medically relevant membrane-mimetic system composed of a polyelectrolyte cushion, a terpolymer, and a self-assembled phospholipid monolayer. Neutron reflectometry is a powerful probe of the compositional depth profile of multilayer structures on planar supports, with a resolution that can be less than a nanometer.

Cell membranes, which form the boundary between extracellular and intracellular compartments, regulate many crucial biological processes. Planar supported mimics of cell membranes are of great interest for the study of membrane structure/function relationships and for the development of biomaterials. The polymeric lipid bilayer membrane under study is being developed as a coating for artificial vascular grafts. The water-swellable polyelectrolyte acts as a support for the biomembrane, not unlike the cytoskeletal support found in mammalian cell membranes. The terpolymer acts as a cushion for the phospholipid layer. The lipid is polymerizable so that it can be anchored to the terpolymer. This gives the membrane mimic stability under shear forces such as those imparted by blood flowing through the vascular system. The goal of this research is to determine the water distribution in the different layers of the biomaterial and to infer if the phospholipid layer exists as a single monolayer on top of the terpolymer. Phase-sensitive neutron reflectometry, developed at the NCNR, makes it possible to directly obtain a unique depth profile of the measured system without any prior knowledge of its composition. NIST's recent neutron reflectometry experiments have shown that the polyelectrolyte cushion layer contains 40% water and the terpolymer layer contains 10% water in a membrane containing just those two layers. However, upon addition of the phospholipid layer, the polyelectrolyte layer becomes less hydrated and the terpolymer layer undergoes significant structural rearrangement. The results also show a 30 A thick layer at the membrane surface, consistent with the formation of a single phospholipid monolayer. This new information now can be used to construct a better polymeric lipid membrane mimic containing a biologically active membrane protein.

CONTACT: Susan Krueger, [phone]; [e-mail] or Chuck Majkrzak, [phone]; [e-mail].