Two experiments were conducted to evaluate hydroxylapatite/polymer composite coatings as bone attachment vehicles for polymers. In the first, bone attachment to two classes of hydroxylapatite (HA) coated polymers was evaluated mechanically and histologically. Particulate HA was molded into the surface of thermoplastic implants and cast into the surface of thermoset implants. Coated and uncoated specimens were implanted in the distal femurs of rabbits for four and twelve weeks. In a second experiment, a roughened surface polysulfone implant was created by imbedding particulate HA into a polysulfone (PS) rod. A second material was created where HA particles were imbedded in the PS rod and the surface of the composite was machined smooth. Smooth and coated implants in both experiments were implanted transcortically in the distal femurs of rabbits for four and twelve weeks.
After sacrifice, the bone/implant interface of all the implants was evaluated mechanically by means of a push-out test with a servohydraulic test system. Paired statistical analysis revealed significantly greater shear strengths for coated versus uncoated implants for both polymer systems (thermoplast and thermoset) at both time periods in the first experiment. The results of the second experiment showed a statistically significant increase in shear strength for the rough surfaced HA/PS implant when compared to the smooth surfaced HA/ PS implant at each time period. Histology at both time periods indicated direct bone apposition to the HA coating as compared to a fibrous encapsulation using the uncoated implants.