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 st udied 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 o f 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 pres sure of 25 mN/m. The transfer efficiency achieved unity at all times. The m orphologies of PEG chains on the phospholipid monolayer in water, in a drie d state, and in a hydrated state were evaluated using Pi-A isotherm, ellips ometry, and atomic force: microscopy (AFM), respectively. When the concentr ation of PEG lipid was below 1 mol %, the PEG chains could cover the DPPC s urface 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 s tate, 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 high ly packed and had a bulky structure at the surface in the dried state as we ll as in the hydrated state. A bulky and extended PEG layer, above 3 mol % concentration, was greatly effective in the prevention of platelet adhesion . (C) 2000 John Wiley & Sons, Inc.