PURPOSE Integration of Boston keratoprosthesis with the surrounding cornea is very important in preventing bacterial invasion which may cause ocular injury. Here we investigate whether hydroxyapatite (HAp) coating can improve keratoprosthesis biointegration, using polymethyl methacrylate(PMMA) – the principal component of the Boston KPro - as a model polymer.

METHODS HAp coatings were induced on PMMA discs after treatment with concentrated NaOH, coating with poly-dopamine (PDA), or coating with polydopamine then with 11-mercaptoundecanoic acid (11-MUA). Coatings were characterized chemically (FTIR, EDX) and morphologically (SEM), and were used as substrates for keratocyte growth in vitro. Cylinders of coated PMMA were implanted in porcine corneas ex vivo for 2 weeks, and the force required to pull them out was measured. The inflammatory reaction to coated discs was assessed in the rabbit cornea in vivo.

RESULTS FTIR of the coatings showed absorption bands characteristic of phosphate groups, and EDX showed that the Ca/P ratios were close to HAp. By SEM, each method resulted in morphologically distinct HAp films; the 11-MUA group had the most uniform coating. The hydroxyapatite coatings caused comparable enhancement of keratocyte proliferation compared to unmodified PMMA surfaces, and induced more ECM secretion. HAp coating significantly enhanced the force required to pull PMMA cylinders out of porcine corneas ex vivo. HAp coating of implants reduced the inflammatory response around the PMMA implants in vivo.

CONCLUSIONS These results are encouraging for the potential of HAp-coated surfaces for use in keratoprostheses.