To resolve these persistent [hip joint replacement replacement] failures, researchers turned their attention towards a bioactive ceramic called hydroxylapatite. This ceramic promised to provide a more hospitable environment for biological bony fixation of prosthetic implants.
Bone is a composite material made up of 60 to 70% inorganic mineral crystal and 30 to 40% organic matrix consisting mostly of collagen protein fibers. The major mineral constituent of bone is hydroxylapatite in the form of tiny elongated crystals. These crystals are combined with the collagen fiber organic matrix of bone in a highly organized fashion and stiffen the bone structure in much the way that glass fibers stiffen softer plastics in the synthetic composite fiberglass.
When the body encounters exposed hydroxylapatite surfaces adjacent to healing bone, the natural response is to form new bone along those exposed surfaces until the healing bone is anchored there. Synthetically prepared hydroxylapatite ceramic has the same chemical composition as this major mineral constituent of bone.
When implanted in sites adjacent to healing bone, it incites this same natural healing response with an actual physical chemical bond forming between the patient's healing bone and the implanted bioceramic. This bond is so strong that once bone has become attached to the surface of this material and samples are stressed to failure, fracture occurs through the bone some distance away from the actual bone ceramic interface.