16.1 Introduction

Hydroxyapatite is a calcium orthophosphate containing water with a chemical composition of Ca ₁₀(PO ₄) ₆(OH) ₂. The composition and structure of hydroxyapatite closely resembles that of mineral components of vertebrate hard tissues. Body fluid is supersaturated with respect to hydroxyapatite under normal physiological conditions. Therefore, the growth and dissolution of hydroxyapatite has an important contribution to ossification, calculus formation, and the development of caries. However, the mechanism underlying biological apatite formation is still not sufficiently clear. In addition to the normal calcifications in bone and teeth, some of the pathological calcifications are also regulated by various factors including cells and matrix proteins.

In this chapter, we first briefly review the calcium orthophosphate family to which hydroxyapatite belongs, although detailed reviews on this subject have already been published by a number of authors [1 5]. Some calcium orthophosphates are formed as precursors that have chemical and structural similarities to hydroxyapatite, and others are used as raw materials for calcium phosphate cements and hydroxyapatite single crystals.

An important aspect of hydroxyapatite growth in modern technology is that, in many cases, the nucleation and subsequent growth of hydroxyapatite on the surface of biomaterials implanted in body tissues determine the performance and even lifetime of biomaterials. For biomaterials used in the repair of bone tissue, the formation of hydroxyapatite on...