DEVELOPMENT OF BIOACTIVE GLASS BASED COMPOSITES FOR CORROSION RESISTANT COATING APPLICATIONS

Abstract

Magnesium and its alloys show great promise as potential biodegradable metals for use in orthopedic applications. However, one significant challenge that has hindered their widespread adoption in medicine is their rapid degradation rate in the physiological environment. This thesis is aimed to explore surface modification strategies that could effectively regulate the degradation rate of magnesium alloys when exposed to physiological environments. Additionally, the study seeks to conduct thorough in vitro assessments and evaluations of the biocompatibility of these modified alloys. The overall thesis is composed of two individual projects. Chapter 1, discusses a brief introduction of magnesium alloy as biodegradable materials and discusses the degradation rate when implanted in human body. Also, presents the approach strategies for surface modification to enhance corrosion resistance, biocompatibility and mechanical integrity of magnesium alloy. Chapter 2, investigates the effect of zein-bioactive glass (BG) nanocomposite on AZ31B magnesium alloy. BG nanoparticles required for zein and BG (zein_BG) composite were synthesized by a bio-inspired method using cetyltrimethylammonium bromide (CTAB) as a template. The formation of BG particles were confirmed by Fourier transform infrared spectroscopy (FTIR) showing characteristic Si-O-Si and Si-O− peaks. Nano-size of BG particles with an average diameter of (6.67 ± 0.06) nm was reported by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) revealed successful deposition of zein and zein_BG coatings on the magnesium alloy surfaces. High resolution X-ray Photoelectron Spectroscopy (XPS) analysis on zein_BG coated Mg alloy immersed in HBSS revealed the corrosion deposition of Mg(OH)2 ,MgHPO4.H2O, CaHPO4.H2O, SiO2 , MgCO3 and CaCO3 on the substrate surface. More than two fold wettability, 95 % adhesion strength, and 14-fold increase in surface roughness were reported for zein_BG coated magnesium alloy compared to the bare surface. Measurements of weight loss and electrochemical measurements in zein and zein_BG coated alloy substrates in Hanks Balanced Salt Solution (HBSS) for 10 d at 37 ℃ showed a drastic decrease in weight loss of substrates after coating. As a result, zein_BG coated substrate was observed to possess the maximum protective efficacy (95.99 %) against corrosion. These findings demonstrated that simple zein_BG composite dip coating was a successful corrosion-resistant implant coating on magnesium alloy surface for orthopedic applications. Chapter 3, the present study reports on a novel multilayer coating for biodegradable magnesium (Mg) alloy substrates. This coating contains soy protein hydrolysate (SPH), poly(allylamine hydrochloride) (PAH), and folic acid (FA) templated bioactive glass (BG) nano particles. The multilayer, designated as SPH/(PAH/BG)n, was coated onto an alkaline treated Mg alloy surface (AMgS) through a dip-coating process with various numbers of cycles (n = 5 and 7) using a layer-by-layer (LbL) assembly. The BG particles had an average diameter of 12.53 ± 2.22 nm and were embedded with therapeutic FA molecules. Scratch testing, wettability, and roughness tests showed excellent adherence of the SPH/(PAH/BG)7 coating on AMgS, making it suitable for cell attachment. Electrochemical measurements in Hanks balanced salt solution (HBSS) demonstrated that the SPH/(PAH/BG)7 coating improved the corrosion resistance of the Mg alloy. SPH/(PAH/BG)7 coated substrate showed a maximum protective efficacy of 98.4041% , thanks to the bioactive nature of BG. High-resolution XPS and XRD analyses on SPH/(PAH/BG)7/AMgS confirmed the corrosion deposition of Mg(OH)2, MgHPO4.H2O, CaHPO4.H2O, SiO2, MgCO3 and CaCO3 on the substrate surface after immersion in HBSS for 10 d at 37 ℃. The LbL coated Mg substrate also showed excellent cytocompatibility by hemolysis assay These results suggest that the SPH/(PAH/BG)7 /AMgS material has multifunctional properties and can be a possible alternative for biomedical applications of Mg alloys. Chapter 4, summarizes the main conclusions and recommendations for future work by use of surface modification (layer by layer ) coating of magnesium alloy.