WHY DO PHOSPHOLIPID POLYMERS REDUCE PROTEIN ADSORPTION

The amount of plasma protein adsorbed on a phospholipid polymer having a 2-methacryloyloxyethyl phosphorylcholine (MPC) moiety was reduced c ompared to the amount of protein adsorbed onto poly[2-hydroxyethyl met hacrylate (HEMA)], poly[n-butyl methacrylate (BMA)], and BMA copolymer s with acrylamide (AAm) or N-vinyl pyrrolidone (VPS) moieties having a hydrophilic fraction. To clarify the reason for the reduced protein a dsorption on the MPC polymer, the water structure in the hydrated poly mer was examined with attention to the free water fraction. Hydration of the polymers occurred when they were immersed in water. The differe ntial scanning calorimetric analysis of these hydrated polymers reveal ed that the free water fractions in the poly(MPC-omega-BMA) and poly(M PC-con-dodecyl methacrylate) with a 0.30 MPC mole fraction were above 0.70. On the other hand, the free water fractions in the poly(HEMA), p oly(AAm-omega-BMA), and poly(VPy-omega-BMA) were below 0.42. The confo rmational change in proteins adsorbed on the MPC polymers and poly(HEM A) were determined using ultraviolet and circular dichroism spectrosco pic measurements. Proteins adsorbed on poly(HEMA) changed considerably , but those adsorbed on poly(MPC-omega-BMA) with a 0.30 MPC mole fract ion differed little from the native state. We concluded from these res ults that fewer proteins are adsorbed and their original conformation is not changed on polymer surfaces that possess a high free water frac tion. (C) 1998 John Wiley & Sons, Inc.