Corrosion behavior and mechanical properties of silicon and zinc-oxide coated magnesium-based bionanocomposite with hydroxyapatite and titania additives
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Date
2016
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Universiti Teknologi Malaysia
Abstract
Magnesium (Mg)-based alloys were emerged as potential biodegradable material for temporary implants. However, their fast degradation in the high chloride environment of the physiological solution is detrimental unless inhibited. These Mg-based implants lose their mechanical integrity before the tissue is being sufficiently healed. Furthermore, the accumulation of hydrogen gas upon fast degradation in a physiological solution restricted their clinical applications. In this view, the present research is targeted to improve the biocorrosion behavior and mechanical properties of pure Mg by alloying it with nanostructured hydroxyapatite (HA), MgO, and TiO2 through milling-pressing-sintering powder metallurgy route. Four different Mg-based bionanocomposites including Mg/HA, Mg/HA/MgO, Mg/HA/TiO2 and Mg/HA/TiO2/MgO were synthesized to evaluate their bioimplantation efficacy. The Mg/HA/TiO2/MgO bionanocomposite was further coated with nano-Si, nano-ZnO single-layer, and nano-Si/ZnO double-layers using radio frequency magnetron sputtering technique to achieve such goal. The influence of varying amounts of the additives, the ball milling duration, the annealing temperature, and the coating agents on the biocorrosion and mechanical properties of these bionanocomposites were evaluated using electrochemical, immersion and compression tests. The phase evolution of the synthesized bionanocomposites before and after immersing in the simulated body fluid (SBF) solution was characterized via X-ray diffraction, Fourier-transform infrared and X-ray photoelectron spectroscopy. The detailed microstructures were determined using field-emission scanning electron, transmission electron, and atomic force microscopies. The bionanocomposites wettability was measured via video contact angle method. Thermal gravimetric and differential thermal analysis were performed to evaluate the activation energy and the reaction kinetics of the prepared powder bionanocomposites. In vitro corrosion resistance was analysed using potentiodynamic polarization, immersion, pH variation, and hydrogen evolution tests. After 8 h of ball milling the corrosion resistance of Mg/xHA/10TiO2/10MgO (wt%) bionanocomposite for two different compositions of HA such as 12.5wt% and 27.5wt% was found to increase from 1.35 and 2.19 kΩ.cm2 to 2.25 and 4.78 kΩ.cm2, respectively. Meanwhile, by annealing at 630°C, these two bionanocomposites demonstrated reduced corrosion rates compared to those annealed at 500°C. Interestingly, the compression failure strain (ductility) of HA incorporated Mg was decreased by increasing milling time. The corrosion rate of Mg/12.5HA/10TiO2/10MgO coated with nano-Si/ZnO exhibited a significant reduction from 5.82 (uncoated) to 0.25 mm/year. The cell culture test authenticated that the Mg-based bionanocomposites appeared biocompatible in the presence of HA, MgO, TiO2 additives and nano-Si/ZnO coating. It is noticed that the synthesized Mg/12.5HA/10TiO2/10MgO coated with nano-Si/ZnO has a great potential to become a candidate for biodegradable implants
Description
Thesis (Ph.D (Biomedical Engineering))
Keywords
Biosciences and medical engineering