Wear characteristic and biocompatibility of some hydroxyapatite–collagen composite acetabular cups

Both HDPE and UHMWPE have long been used successfully as socket materials in hip-joint replacements. Recently, however there are concerns over the adverse biological responses due to the wear debris of these polymers. Although a good deal of work to improve the performance of these polymers has been carried out a need still exists for an implant material with improved biocompatibility and mechanical properties. Hydroxyapatite–collagen composites have been prepared by precipitation of calcium phosphate on collagen in the past but very few of these attempts considered the mechanical strength of the composites that suits their realistic uses as implant material. Present work is an attempt to develop hybrid composites of hydroxyapatite–collagen–hyaluronic acid or gelatin with sufficient adherence to both hard and soft tissues and also with good cohesive strength leading to improved mechanical and biological properties. It was possible to prepare acetabular cups of the newly developed composites by compression moulding for tests on a hip-joint simulator. Pin specimens for tests on a pin-on-disc apparatus were also moulded with these composites. Tests with the acetabular cups and pin specimens indicate that some of the newly developed materials offer wear resistance comparable to those of the presently used socket materials. Biocompatibility tests with these materials show that their haemolysis counts are well below the acceptable range. Hydroxyapatite–collagen composites with 10% hyaluronic acid offer suitable mechanical strengths, good friction and wear characteristics and acceptable level of haemolysis and therefore the composite may be considered to be a potential socket material of future generation.