Solution hydroxyapatite coatings

Nanocrystalline hydroxyapatite coatings were deposited by plasma spraying of sols formed from various precursor solutions by Coyle et al. (2007). The coatings were designed to possess improved resorption in vivo and thus reduced the risk of forming larger debris particles that may give rise to particle disease . 

Kuroda, K., Ichino, R., Okido, M., and Tokai, O. (2002b) Hydroxyapatite coating on titanium by thermal substrate method in aqueous solution. Biomed. Mater. Res., 59 (2), 390-397. 

J.C., and Meletis, E.I. (2001) Effects of solution pH and electrical parameters on hydroxyapatite coatings deposited by a plasma-assisted electrophoresis technique. 

J., and Yakovin, S. (2014) Formation of solution-derived hydroxyapatite coatings on titanium alloy in the presence of magnetron-sputtered alumina bond coats. Open Bioeng. J., in press. 

Figure 7.19 Cathodoluminescence images of an as-sprayed hydroxyapatite coating cross-section (a) and CL images of coatings immersed in Hank s Balance Salt Solution (HBSS) for 7 days (b) and 28days (c).

Pure magnesium substrates were chemically pretreated at 70 °C with a Ca/Na phosphate solution to obtain a porous brushite layer and subsequently PEO at a voltage of 450 V, a frequency of 1000 Hz and a duty cycle of 40% to deposit strontium-containing hydroxyapatite (Lu et al., 2014). Figure 7.59 shows that the Sr-hydroxyapatite coating provided improved corrosion resistance in HBSS to the pure Mg substrate. The characteristic corrosion parameters are presented in Table 7.6. 

Table 9.21 Effect of hydroxyapatite coatings and calcium phosphate solutions on the corrosion resistance of titanium and stainless steel...

There are several reports on the coating of bone-like hydroxyapatite onto natural polymer substrates. Kawashita et at. [57] reported that carboxymethylated chitin and gellan gum gels, which have carboxyl groups, can form hydroxyapatite on their surfaces in SBF if they are treated with a saturated Ca(OH)2 solution in advance, while curdlan gel, which has no carboxyl group, does not form hydroxyapatite in SBF, even if it is treated with Ca(OH)2 solution. These results support the hypothesis that carboxyl groups induce hydroxyapatite nucleation. Kokubo et at. [58,59] reported that non-woven fabrics of carboxymethylated chitin and alginate fibers also form hydroxyapatite on their surfaces in SBF if they are treated with Ca(OH)2 solution. 

Fig. 10. Scanning electron microscope (SEM) micrograph of the surface of vacuum plasma sprayed hydroxyapatite (HA) coating after treatment in the fluoridating solution (KF 0.05 M KH2PO4 0.15 M pH 7, temperature 100 C). A layer of thin needle-like fluorhydroxyapatite crystals (0.5-3 m long, 0.1-0.3 m width) can be observed. (With kind permission of Springer Science and Business Media).

Fujishiro, Y., Sato, T., and Okuwaki, A., Coating of hydroxyapatite on metal plates using thermal dissociation of calcium-EDTA chelate in phosphate solutions under hydrothermal conditions, 7. Mater. Sci. Mater. Med., 6, 172, 1995. 

Teeth have a protective coating of hard enamel that is about 2 mm thick and consists of about 98% hydroxyapatite, Ca5(PO4)3011. Like any ionic solid surrounded by a water solution, the hydroxyapatite is constandy dissolving and reprecipitating. 

A supersaturated bioinspired solution was used to coat alumina and zirconia substrates with a thin, poorly crystalline layer of OCP that after heat treatment at 1050 °C for 1 h was converted to hydroxyapatite with particle size of 300 nm (Pribosic, Beranic-Klopcic and Kosmac, 2010). Stefanic et al. (2012) applied a related method to rapidly deposit an OCP layer by a two-step process onto yttria-stabilised tetragonal zirconia polycrystal (Y-TZP). 80vol% Mg-PSZ/20 vol% alumina substrates were used by Nogiwa and Cortes (2006) to deposit biomimetically by immersion in 1.4 SBF a bone-like apatite coating of 15-30 pm thickness, using a bed of either wollastonite ceramics or bioactive glass as an additional source of Ca2+ ions. 

---