Atmospheric hydroxyapatite coating

Figure 5.32 SEM images of conventional atmospheric plasma sprayed (APS, left) and suspension plasma sprayed (SPS, right) hydroxyapatite coatings, (a, b) Top view and (c, d) coating cross-sections (Gross and Saber-Samandari, 2009). ( With permission by Elsevier.)...

A notable exception is a study by Hesse et al. (2008) who investigated the effect of powder grain size and grain size distribution on the spatial distribution of calcium phosphate phases in atmospheric plasma-sprayed hydroxyapatite coatings incubated in r-SBF (SBF-H, Table 7.8). Coatings were mechanically abraded under dry conditions in steps of 40 pm by abrasive SiC paper, and the newly created surfaces analysed by XRD with Rietveld refinement for their quantitative phase composition. The results of this depth profiling are shown in Figure 6.8. 

In the field of metallic powder applications, a method of plasma spray coating suitable for biomedical materials has been developed using titanium and calcium phosphate composite powder. By means of the mechanical shock process, the appropriate composite powder was prepared, and plasma sprayed on Ti substrate under a low-pressure argon atmosphere. A porous Ti coating layer was obtained in which the surface and the inside of the pores were covered thinly with hydroxyapatite. This surface coating is expected to show excellent bone ingrowth and fixation with bone (21). 

Hydroxyapatite/titania layers were spin-coated on the surface of TiZr alloy at a speed of 3000 r.p.m. for 15 s, followed by a heat treatment at 600 °C for 20 min in an argon atmosphere (Wen et al., 2007). The coating displayed excellent bioactivity when soaked in a SBF for an appropriate period. Differential scanning calorimetry, TGA, XRD and SEM in conjunction with energy dispersive spectroscopy were used to characterise the phase transformations and the surface structures and to assess the in vitro tests. The titania (anatase) layer exhibited a cracked surface and the HAp layer showed a uniform dense structure. Both layers were about 25 im thick. 

Park, E. and Condrate, R.A. (1999) Graded coating of hydroxyapatite and titanium by atmospheric plasma spraying. Mater. Lett., 40, 228-234. 

Slosarczyk et al [229] used PAN based carbon fibers, both uncoated and coated, with calcium phosphate applied by a sol gel technique. Carbon fiber reinforced hydroxyapatite composites were then prepared by hot pressing hydroxyapatite powder and carbon fibers at 1100°C and 25 MPa for 15 min in an Ar atmosphere. The best strength properties were obtained with the eoated fibers and were attributed to the —OH groups on the fiber surface bonding with the ealeium phosphate layer. 

It is likely that cordierite, titanate and zirconate ceramics will record the most rapid rates of growth, due to their uses in environmental systems, medical products, electronic components, and household appUances. A continued expansion in electronic component shipments will provide opportunities for titanate per-ovskites and other ceramics. Nonetheless, cordierite, titanates and other ceramics will undoubtedly benefit from a continued, environmentally driven trend to reduce the amounts of particulates, nitrogen oxides (NO,), and sulfur oxides that are released into the atmosphere. Technological advances in the medical product market will also provide many opportunities, notably for monohthic ceramics such as alumina and zirconia used for femoral balls in hip endoprostheses, as well as biocompatible hydroxyapatite and tricalcium phosphate coatings for the metal stems of hip implants (see also Chapter 10). Likewise, dental ceramics wiU continue to experience high growth rates through 2010. 

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