Preparation of a PEG-grafted phospholipid Langmuir-Blodgett monolayer for blood-compatible material.

In order to develop a versatile model for blood-compatible materials, we studied morphology and platelet adhesion of a dipalmitoyl-phosphatidylcholine (DPPC)/dipalmitoyl-phosphatidylethanolamine-polyethylene glycol (PEG lipid) mixed monolayer. This monolayer, which mimics the cell membrane structure, consists of two heterogeneous layers, that is, a PEG layer lying on top of a phospholipid monolayer. The DPPC/PEG lipid mixed monolayer was prepared using the Langmuir-Blodgett (LB) Technique. The monolayer was transferred onto a silanized glass substrate by the down-stroke mode, at a surface pressure of 25 mN/m. The transfer efficiency achieved unity at all times. The morphologies of PEG chains on the phospholipid monolayer in water, in a dried state, and in a hydrated state were evaluated using Pi-A isotherm, ellipsometry, and atomic force microscopy (AFM), respectively. When the concentration of PEG lipid was below 1 mol %, the PEG chains could cover the DPPC surface completely in water, but not in the dried state. On the other hand, the PEG chains could cover the phospholipid surface completely in a dried state, as well as in water, when the PEG lipid concentration was above 3 mol %. These PEG chains, showing a brush-type conformation in water, were highly packed and had a bulky structure at the surface in the dried state as well as in the hydrated state. A bulky and extended PEG layer, above 3 mol % concentration, was greatly effective in the prevention of platelet adhesion.