INFLUENCE OF PREADSORBED BLOCK-COPOLYMERS ON PROTEIN ADSORPTION - SURFACE-PROPERTIES, LAYER THICKNESS, AND SURFACE COVERAGE

In this article the influence of preadsorbed block copolymers on lipas e adsorption is studied. The Pluronic triblock copolymers used in this study (P75 and F108, respectively) both have one hydrophobic (poly(pr opylene oxide)) block in the middle and two hydrophilic (poly(ethylene oxide)) blocks at the ends of the molecules. It was concluded that bl ock copolymers adsorb onto a hydrophobic surface with the middle block ; the buoy groups are extended into the water, thus forming a brush. T he hydrodynamic layer thickness of F108 is 10 nm. At a hydrophilic sur face the buoy groups adsorb and a flat pancake configuration is formed . The hydrodynamic layer thickness is 1 nm. Protein (lipase and bovine serum albumin) adsorption is prevented by F108, provided this is adso rbed in a brush configuration; a pancake configuration is not effectiv e. Prevention of protein adsorption is not solely caused by the presen ce of F108 at the surface; above that the configuration of the adsorbe d molecule is essential. The steric repulsion caused by a brush is str onger than that caused by a pancake. The effect of brush density on pr otein adsorption has been systematically studied for the F108/lipase s ystem. Both the protein adsorption rate and the final adsorption level were measured as a function of the amount of preadsorbed F108. It is found that small amounts of adsorbed F108 (10% saturation of the surfa ce) reduce the initial adsorption rate of lipase severely (approximate ly 20-fold). The maximum value of the adsorbed amount at such a surfac e is 3 times lower as compared to a ''bare'' surface. It can therefore also be concluded that protein binding to the surface is already hind ered by low levels of preadsorbed block copolymer. In the case of a sa turated F108 layer no protein adsorption takes place.