Release and retention of biomolecules in collagen deposited on orthopedic biomaterials

Delivery of osteotropic biomolecules directly to the bone-implant interface can alter initial interactions between tissue and biomaterial. To this end, type I collagen coatings containing a model biomolecule, lysozyme, were deposited on Co-Cr-Mo and Ti-6Al-4V. Two deposition methods were examined. In the first, lysozyme was deposited concurrently with collagen, while in the second, protein was impregnated into previously deposited collagen coatings. The amount of collagen and the amount of lysozyme loaded into collagen were varied to provide different amounts of weakly and strongly bound protein. Release and retention of lysozyme were monitored over a 7 d period of incubation in physiological saline. For both methods, larger amounts of collagen in the coatings allowed incorporation of more lysozyme. Additionally, loading collagen coatings with greater amounts of lysozyme resulted in release of more protein. During the first 24-96 h of incubation, loosely bound protein was eluted, resulting in release of 2 micrograms to 55 mg (5-75% of the amount available) of enzymatically active lysozyme. This left 25-95% of the protein bound to the collagen-coated biomaterials and, thus, available for later release during degradation of the collagen.