Surface modification with hydrogels via macroinitiators for enhanced friction properties of biomaterials

A general method of surface modification is described which is based on dip-coating of a substrate with a macroinitiator and subsequent free radical polymerization of functional monomers. Using this method, it is possible to fix poly(acrylic acid) hydrogels on polymer surfaces, e.g. on catheters, which drastically reduces the friction of these materials. Similarly, other biological relevant properties, especially reduced protein or bacteria adsorption can be achieved by choosing appropriate monomers. The substrate was first homogeneously dip-coated with e.g. the water-insoluble macroinitiator poly(octadecene-co-maleic anhydride), partially reacted to the tert.-butyl perester. Homogeneity, thickness, and reactivity of the macroinitiator layer was characterized in detail. After a temper step, surface homo- and copolymerizations of ionic monomers were carried out in water directly from the modified surface. The consistency of the hydrogel coating could be well controlled by the reaction conditions and the monomer composition. The correlation between the experimental parameters, the composition of the surface coating, and the friction properties was established. A relatively thick, slightly crosslinked poly(acrylic acid) hydrogel coating reduces the friction coefficient by 95% compared to that of uncoated surfaces.