Physico-Chemical and Mechanical Characterization of Bioactive Ceramic Coating

The research problem the solution of which has been attempted in my dissertation is multidisciplinary in nature. This includes a lot of interfacial subject areas e.g. biomedical science and engineering, nanotechnology, mechanical engineering as well as materials science and engineering. The problem has originated from a critical biomedical engineering issue e.g. loosening of metallic prosthesis fixed with the Polymethylmethylacrylate bone cement especially in the case of hip joint replacement which ultimately causes the patient to undergo the painstaking revision surgery. Then the engineers produced a cementless fixation introducing a bioactive hydroxyapatite (i.e. the main inorganic constituent of the bone and teeth) coating on the metallic implants. A wide variety of different coating methods has been developed to make the HAP coating on metallic implants more reliable, of which; ultimately the plasma spraying method has been commercially accepted. However, the story was not yet finished at all; a lot of questions came out regarding coating adherence, stability and bio-functionality in both in vitro and in vivo environments. Moreover, it has been now realized that the conventional high power plasma spray (i.e. macroplasma) coating method renders plenty of disadvantages in terms of poor crystallinity that hinders bio-resorption, phase impurity, lesser porosity that hinders osseointegration and residual stresses which ultimately lead to inadequate mechanical properties and delamination of the coating. Therefore, in the present thesis the low power plasma spraying i.e. the microplasma spraying method developed very recently; has been utilized to coat hydroxyapatite on SS316L substrates for minimizing the aforesaid problems associated with the conventional, commercial Macroplasma sprayed vi hydroxyapatite coatings. Surgical grade SS316L has been chosen as the substrate material because it is more cost effective than Ti-6Al-4V and CoCrMo alloys. In the present work, systematic studies have been carried out from processing of microplasma sprayed hydroxyapatite coating to it’s actual in vivo application. To the best of the author’s knowledge, the present thesis work in the area of microplasma sprayed hydroxyapatite coating on SS316L substrate, the related physico-chemical, in vitro and in vivo characterizations as well as evaluation of the mechanical properties at the microstructural length scale utilizing the nanoindentation technique is probably the first such attempt and I hope that the present work marks the beginning of a journey in this area.