Surface Modification of Magnesium and its Alloys for Orthopedic Applications

In recent years, Magnesium (Mg) and its alloys as bioresorbable metals have attracted increasing attention for orthopedic implant applications because of their promising mechanical and biological properties. However, the rapid degradation of pure Mg remains a key challenge toward its clinical translations. Additionally, implant infections continue to be a significant clinical problem for orthopedic applications. This dissertation develops two approaches to improve the overall performance of pure Mg. One method includes engineering a nanostructured oxide surface onto the Mg coupled with adding alloying elements into the Mg matrix, the other involves depositing a nano-micro and micro hydroxyapatite supplemented with gentamicin onto the Mg. The nanostructured oxides on Mg alloy and pure Mg resulted in a slower electrochemical degradation rate, and reduced adhesion of methicillin-resistant Staphylococcus aureus (MRSA) on their surfaces when compared with the corresponding non-treated Mg controls. Moreover, the soluble degradation products released from nanostructured oxides on the Mg alloy and pure Mg did not affect the growth of bone marrow derived mesenchymal cells (BMSCs) under indirect contact, but showed reduced cell spreading and adhesion under direct contact when compared with Ti control and glass reference. In terms of the nano-micro and micro hydroxyapatite supplemented with gentamicin coated Mg, the 12-week immersion study showed that the difference in the degradation rate between the hydroxyapatite coated Mg samples and the Mg controls is negligible because no statistically significant difference was found. The micro hydroxyapatite coated Mg samples did not affect the growth of BMSCs under indirect contact, but showed reduced cell spreading and adhesion under direct contact when compared with the Ti control and glass reference. The micro hydroxyapatite supplemented with 30 wt. % gentamicin coated Mg exhibited significantly lower adhesion of Staphylococcus aureus on the surface among all samples in vitro. Overall, this dissertation provides extensive knowledge regarding surface treatments on Mg and applying alloying elements into Mg to achieve desired performance toward clinical translations