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2. ENGINEERING AND TECHNOLOGY
Magnesium (Mg) and its alloys have been widely explored for orthopaedic applications due to its biodegradable nature, biocompatibility and closely related mechanical properties with bone. However, rapid degradation of Mg alloys under physiological conditions is a major challenge for biomedical industries and clinicians. Amongst the various methods employed, deposited coatings have been widely favoured to enhance the corrosion resistance and compatibility of the Mg alloys. This study focused on developing multifunctional coatings on AZ31 Mg alloy having a corrosion resistant, osteoinductive and antibacterial properties for orthopaedic applications. The aim of this study was achieved through the following objectives: - Fabrication of corrosion resistant and biocompatible PLGA-silane coatings on AZ31. - Preparation of Biomimetic Hyaluronic acid functionalized silane coatings on AZ31. - Fabrication of osteoinductive and antibacterial Hyaluronic acid-lysozyme composite coatings on AZ31. - Effect of hyaluronic acid molecular weight and Mg2+ on osteoblast functions in vitro. Overall, this body of work presented: - Successful assembly of multilayer PLGA coating associated with the amine-terminated MTES-TEOS- APTES silane on the AZ31 Mg alloy. - PLGA-silane coating improved the corrosion resistance of AZ31 Mg alloy in DMEM by ~2 of magnitude (impedance magnitude and corrosion current density) as confirmed by the electrochemical corrosion studies. Similarly, immersion studies showed ~5-fold increase in the corrosion resistance of PLGA-silane coated AZ31 Mg alloy over uncoated AZ31 equivalents. - In comparison to the uncoated AZ31 substrate, osteoblasts showed ~2 to 4-fold increase in the proliferation and differentiation of osteoblast cells cultured on the PLGA-silane coated AZ31 substrates for 14 days. - To further evaluate the corrosion resistant properties of silane coated-AZ31 Mg alloy in the high corrosive electrolyte, the electrochemical corrosion and immersion studies were conducted in HEPES buffered DMEM. The EIS analysis showed an increase in the magnitude of impedance by ~ 2 order of magnitude for MTES-TEOS- APTES modified AZ31 substrate when compared to the uncoated AZ31 equivalents To improve the cytocompatibility of AZ31 Mg alloy by providing a biomimetic environment, high molecular weight hyaluronic acid (HA) was coupled to the amine-terminated MTES-TEOS-APTES modified AZ31 substrate. The high molecular weight HA enhanced the proliferation and differentiation of osteoblasts cells by ~ 4 to 6-fold as compared to the uncoated AZ31 Mg alloy. - Furthermore, the effect of high and low molecular weight of HA and Mg2+ on osteoblast functions was evaluated. It was observed that the high molecular weight HA and Mg2+ synergistically improve the proliferation and differentiation of osteoblast cells by stimulating intracellular calcium ions. - The concerns of bacterial colonisation on Mg-based biodegradable alloy without compromising osteoblast functions was addressed by modifying the amine terminated silane coating with HA-lysozyme (HA-LZ) composite. LZ component of composite significantly reduced the colonisation of S.aureus in a concentration-dependent manner by ~ 30 fold when compared to the uncoated AZ31 equivalents. Whereas, HA component of the composite maintained the osteoblasts cellular response in terms of adhesion, proliferation and differentiation. Hence, the developed multifunctional coatings improved the corrosion resistance, osteoinductive and anti-bacterial properties of the AZ31 Mg alloy.
All work in this thesis has been published.
Agarwal, S. (2018) Multifunctional Coatings for Biodegradable Biomedical Devices. Doctoral thesis, TU Dublin, 2018.