Development of europium-doped calcium silicate coating for bone tissue engineering applications / Kee Chia Ching

Kee , Chia Ching (2022) Development of europium-doped calcium silicate coating for bone tissue engineering applications / Kee Chia Ching. PhD thesis, Universiti Malaya.

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Abstract

Calcium silicate (CaSiO3 or CS) ceramics are promising bioactive ceramics for coatings on metallic implants (titanium and its alloys) for bone regeneration to overcome their inert properties. Yet, their rapid dissolution rates lead to poor chemical and mechanical stability of the implants. Thus, chemically modified CS ceramics are developed to overcome their drawbacks without impairing their bioactivity. Europium (Eu) ions have been identified as promising doping candidates into bioactive ceramics to achieve different biological and functional properties. In this research, Eu–CS coatings with improved mechanical properties, lower dissolution rate and enhanced bioactivity were successfully fabricated for potential application in bone tissue engineering. The precursor of CS, calcium silicate hydrate (CSH), doped with various amount of Eu, was synthesized via hydrothermal and coprecipitation methods. Subsequently, both synthesis methods were compared. The hydrothermal method produced xonotlite while coprecipitation gave 11 Å tobermorite. Regardless of the synthesis method, incorporation of Eu inhibited the crystallite growth and particle size of the as-synthesized powders, while increasing their thermal stability. In both phases, Eu3+ was found to occupy the cation sites in preference to Ca2+. Comparing both synthesis methods, the hydrothermally synthesized powders were of higher crystallinity and thermal stability than the powders prepared by coprecipitation. Moreover, Eu–CSH powder by hydrothermal exhibited stronger photoluminescence intensity than the one by coprecipitation, primarily attributed to its higher degree of crystallinity. Thus, they showed higher potential for nanomedicine application where a combination of biocompatibility and light emission is desired. Powders of Eu–CSH by hydrothermal method were electrophoretically deposited (EPD) on titanium substrates, and calcined, in order to obtain Eu–CS coatings. Their chemical, structural, mechanical and biological properties were evaluated. Doping Eu into CS altered the particle shape and morphology of the coatings, where a low amount of Eu gave a relatively denser coating, while a higher amount gave a more porous one. An Eu doping of 2.5 mol% gave the optimal coating adhesion strength. All Eu–CS coatings provided sufficient apatite forming ability, yet lower degradation rate, as compared to CS coating. Eu2.5CS induced formation of calcium-deficient apatite with a Ca/P ratio of 1.43, close to biological apatite with a ratio of ~1.7. The effect of Eu doped CS on human fetal osteoblast (hFOB) cells were investigated in vitro as well. It was observed that hFOB cells could attach and proliferate on all Eu–CS coatings, suggesting the low or absent cytotoxicity of the coatings. A low amount of Eu doping (2.5 mol%) not only showed comparable cell proliferation with CS, but also enhanced the osteogenic activity of the CS coating.

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