Improvement in crystallinity of apatite coating on titanium with the insertion of CaF2 buffer layer

Abstract

In the apatite coatings on Ti the heat treatment process is necessary to crystallize the apatite structure for improved chemical stability and biological properties. However, the heat treatment normally degrades the mechanical strength of the coating layer associated with thermally induced stress. In this study, we aimed to improve the crystallization of apatite coating by using calcium fluoride (CaF 2 ) as a buffer layer. The insertion of a thin layer of CaF 2 (0.2-1 lm) between apatite and Ti significantly improved the crystallization behavior of apatite. Moreover, this crystallization was more enhanced as the thickness of CaF 2 was increased. When a 1 lm-thick CaF 2 was inserted, the crystallization of apatite initiated at a temperature as low as 320°C, being a dramatic improvement in the crystallization when considering the crystallization initiation temperature of a bare apatite coating on Ti was *450°C. As a result of this crystallization enhancement, the dissolution behavior of CaF 2 -inserted apatite coatings was more stable than that of the bare apatite coating, showing much reduced initial-burst effect. Preliminary cellular assay showed the CaF 2 -inserted apatite coating provided a substrate for cells to spread and grow favorably, as being similar to the bare apatite coating. This novel way of apatite coating on Ti using CaF 2 buffer layer may be useful in the coating systems particularly requiring low temperature processing and increased crystallinity with high chemical stability.

Characterization of nano-structural and nano-mechanical properties of osteoarthritic subchondral bone

“…This supports the notion that sclerotic trabecular bone had a denser structure and stiffer property than the grade I OA trabecular bone that had suffered osteoporosis [43]. Furthermore, increased crystallinity of the mineral phase increases the chemical stability of the crystals [44] and leads to reduced rates of bone turnover in sclerosis and, therefore, results in stiffer bone material property than the grade I trabeculae. Using micro-indentation testing and electron probe microanalysis of the hip, Coats et al has shown a reduced hardness and elastic modulus in OA bone when compared to osteoporotic bone [45].…”

“…Increased intra-fibrillar mineral density also results in the fibrils having less ductility and being subjected to greater compressive stress. Furthermore, increased crystallinity of the mineral phase renders higher stiffness to bone, and increased chemical stability of the crystals leads to reduced rates of bone turnover in sclerosis [44]. …”