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 lipase adsorption is studied. The Pluronic triblock copolymers used in this study (P75 and F108, respectively) both have one hydrophobic (poly(propylene oxide)) block in the middle and two hydrophilic (poly(ethylene oxide)) blocks at the ends of the molecules. It was concluded that block copolymers adsorb onto a hydrophobic surface with the middle block; the buoy groups are extended into the water, thus forming a brush. The hydrodynamic layer thickness of F108 is 10 nm. At a hydrophilic surface 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 adsorbed in a brush configuration; a pancake configuration is not effective. Prevention of protein adsorption is not solely caused by the presence of F108 at the surface; above that the configuration of the adsorbed molecule is essential. The steric repulsion caused by a brush is stronger than that caused by a pancake. The effect of brush density on protein adsorption has been systematically studied for the F108/lipase system. 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 surface) reduce the initial adsorption rate of lipase severely (approximately 20-fold). The maximum value of the adsorbed amount at such a surface is 3 times lower as compared to a ''bare'' surface. It can therefore also be concluded that protein binding to the surface is already hindered by low levels of preadsorbed block copolymer. In the case of a saturated F108 layer no protein adsorption takes place.