FUNDAMENTALS OF HYDROXYAPATITE AND RELATED CALCIUM PHOSPHATES - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 43

(a) (b)

Figure 2.14. Histological micrographs showing carbonate apatite granule (A) and sintered
hydroxyapatite (HAP) granule (B) 12 weeks after implantation in rat calvaria (toluidine blue
staining). Bar = 100 μ m. C: carbonate apatite; H: sintered HAP; nb: new bone; pb: parietal
bone. The sizes of the carbonate apatite and HAP granules before implantation were similar.
(See color insert.)

Figure 2.15. In vivo transformation of calcium phosphate ceramic (H) to carbonate apatite
nanocrystals (c) similar to bone apatite [64,67,88].

similar to that of serum [54]. In vivo , bioactivity is characterized by the formation
of carbonate apatite on the surface of the material resulting from the partial
dissolution of the calcium phosphate ceramic (Figure 2.15), reacting with the elec-
trolytes in the biological fl uid and forming carbonate apatite similar to bone apa-
tite [33,67,88]. Osteoconductive property is the ability of the calcium phosphate
material to act as a template guiding the growth of the new bone (Figure 2.14).
Appropriate geometry and combination of interconnecting macroporosity and
microporosity, apatite (Figure 2.16) can impart osteoinductive (ability to induce
de novo bone formation) properties [53]. However, the exact geometry and
appropriate combination of macro- and microporosities are yet to be established.