**6.1.6. Iron-substituted apatites**

**6.1.3. Copper-substituted apatites**

**6.1.4. Nickel-substituted apatites**

**6.1.5. Zinc-substituted apatites**

antimicrobial activity [3].

tion of Cl<sup>−</sup> or NO3

apatite structure.

to 10, could be described by the following equation:

Copper-substituted hydroxyapatite (Ca10−xCux(PO4)6(OH)2 (where *x* = 0.05 – 2.0) and fluorapa‐ tite Ca10−xCux(PO4)6F2 (*x* = 0.05 – 2.0) were synthesized by SHANMUGAM and GOPAL [29] via the co-precipitation method and subsequent thermal treatment to 700°C for 30 min. Due to its antimicrobial activity, the copper-substituted fluorapatite could be applied as an antimicro‐

According to MOBASHERPOU et al [30], the reaction mechanism corresponding to equimolar exchange of nickel and calcium and yielding to Ca10−xNix(PO4)6(OH)2, where *x* varies from 0

( ) ( ) ( ) ( ) <sup>2</sup>

In this process, Ni2+ ions are first adsorbed onto the surface of hydroxyapatite (surface complexation, **Section 6.5.2**) and then the substitution of Ca2+ for Ni2+ ions takes place.

Zinc is a common bioelement. The zinc content in human bones ranges from 0.0126% to 0.0217% by weight [7]. Zinc as a cationic substituent in hydroxyapatite provides the option to counteract the effects of osteoporosis [31]. The incorporation of zinc into the HAP structure (Zn-HAP) was abundantly studied, owing to the key effect of Zn2+ cations in several metabol‐ ic processes that makes zinc eligible for use in many biomedical applications and to its possible

The results of structure analysis indicated that Zn ions substituted partially for Ca ions in the apatite structure and the upper limit of Zn substitution for Ca in HA was about 20 mol.%. In

4

<sup>−</sup> into the structure of apatite. This can be avoided by the utilization of acetate

(3)

general, the HAP lattice parameters, *a* and *c*, decreased with Zn addition [32].

( ) ( ) ( ) ( )

10x 10 1 x 4 6 2

Ca Zn PO OH


Zn-substituted apatite was synthesized by the precipitation method as follows [33]:

2 2 3

10x Ca 10 1 x Zn 6 PO 2 OH

+ + --

+- + + ®

where 0 ≤ *x* ≤ 1. The pH of the solution was adjusted to 8 by aqueous solution of NH3, and the reaction mixture was kept at 90°C for 5 h with stirring. The resulting suspension was then subjected to suction filtration, and the powdery product was dried at 100°C for 10 h. It is known that the usage of chloride or nitrate of calcium as a starting reagent may cause the incorpora‐

salts, because acetate ions are not incorporated into the apatite, i.e. they would not affect the

10 4 6 2 10 x x 4 6 2 Ca PO OH x Ni Ca Ni PO OH x Ca <sup>+</sup> + ® - <sup>+</sup> (2)

bial biomaterial for various purposes like orthopedic and dental implantations.

298 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

The synthesis and the characterization of iron-substituted hydroxyapatite via a simple ionexchange procedure were described by KRAMER et al [34]. Using a ferric chloride solution and a simple soaking procedure, FeHAP can be prepared with no apparent formation of the second phase. The substitution of Fe3+ into the HAP lattice results in FeHAP powders with magnetic properties. This novel simplified room temperature soaking procedure can be applied in the future to synthesize magnetic apatite-based nanoparticles for biomedical applications.
