Functionally adapted surfaces on a silicone keratoprosthesis

Silicone intraocular lenses as well as silicone sponges and encircling bands on the bulbar surface are widely used and are well tolerated. The aim of this project is a new one-piece silicone keratoprosthesis with enhanced cell adhesion in the haptic region to optimize the keratoprosthesis stability. These investigations show how enhanced profileration of conjunctival fibroblasts and, therefore, improved tissue compatibility can be achieved by hydrophilizing and by protein immobilisation on a hydrophobic silicone surface. This allows a combination of desired chemical and mechanical properties of the silicone bulk material with surfaces of improved tissue compatibility.

Silicone foils with surface modifications of different kinds were tested. Experiments were done using cell cultures with murine fibroblasts L-929 and human conjuctival fibroblasts. Cytotoxicity assays were carried out with cells grown on the material in direct contact, as well as in indirect contact, with extracts (EN 30993-5). Viability stains by means of fluoresceindiacetate and ethidiumbromide together with morphology analyses by hemalaun-staining were performed.

For the unmodified and modified foils themselves and their extracts any negative influence on cell cultures of murine and human cells could be excluded. There was a gradual improvement of cell morphology, spreading and proliferation dependent on the degree of surface modification. Covalently immobilised fibronectin showed the best results in contrast to adsorptive binding.

Silicone surfaces can be modified chemically with bioactive proteins. These modifications are cell compatible and do not result in toxic reactions. The degree and type of silicone hydrophilization results in improved development of cell morphology, spreading and proliferation. Even better results are obtained after covalent binding of bioactive proteins like fibronectin. Improved biocompatibility with enhanced cellular overgrowth has been demonstrated in vitro for the modified silicone of the haptic region. We believe that this type of modification will help in reducing extrusion problems observed with former keratoprostheses.