In 1974, it was found that sintered hydroxyapatite has a good biocompatibility in a dog's femur and mandible bones. Since then, hydroxyapatite has been studied as a biomaterial for artificial bones, cement and tooth roots.
Now, bone fillers made of hydroxyapatite are used clinically worldwide. In 1982, it was clarified that sintered hydroxyapatite has also a good compatibility with skin tissue. Since then, percutaneous devices based on hydroxyapatite have been developed, and the applications have been expanded to CAPD dialysis, blood pressure measurement, blood access for nutrition, and so on.
Hydroxyapatite has various types of crystal faces, including (100), (010), and (001) faces. The surfaces of these faces are very different in atomic elements, numbers, and arrangements. Therefore, their surfaces are also different in biocompatibility. We must design the crystal surfaces of hydroxyapatite according to its functions. In this paper, the crystal and surface structures of hydroxyapatite are described, and the relationship between the surface structure and biocompatibility is discussed.
