Development of silane based coating for corrosion protection of magnesium alloy for biomedical implant application

2017-03-01T23:35:26Z (GMT) by Gaur, Swati
Biomaterials are used in several medical applications today, such as fixation devices, replacements and surgical equipment. Implants are typical examples of a biomaterial application and there are several different implant materials used today. Conventional implant materials include stainless steels, cobalt-chromium alloys, alumina, polymers (methyl methacrylate), polyethylene etc. There are several impediments associated with long term presence of implants inside body, including allergy and sensitization. After the healing and curing, the implant is removed by a second surgery which is not only costly but also very painful. To make this process simpler, less painful and cost effective, there is a need for alternative methodology, called the use of temporary biodegradable implants. The purpose of biodegradable implant is to support tissue regeneration and healing by material degradation and simultaneous implant replacement through the surrounding tissues. In recent years there has been increased amount of focus on magnesium and its alloys for their potential use as biodegradable implant materials. Magnesium is biocompatible; has excellent mechanical properties; is natural for human body, and seems to stimulate new bone formation. However, a serious problem with magnesium is its high corrosion rate with consistent hydrogen gas formation which delays the healing process. Hence, there is need for controlling their degradation rate, by some surface modification. In this research work magnesium based alloy system containing calcium and zinc was investigated (Mg-6Zn-Ca alloy) which are supposed to be non-toxic in the body. The work focused on to mitigate/delay the corrosion rate of the alloy by development of silane based coating systems for effective corrosion resistance and selecting the coating chemistry to provide biocompatibility. Two different types of silane based coating systems were studied and developed. Phosphonato silane approach (DEPETES with MTEOS and BTESPT as precursor) and non-Phosphonato silanes approach (GPTMS with MTEOS) were used to develop coating. As developed coatings were subjected to various detailed characterization techniques like, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) and the cross-linking in the coating was studied using Fourier transform infrared spectroscopy (FTIR)and performance evaluation, using Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic polarization, hydrogen evolution and pH change. Further, biological response of human osteoblast cell line on the developed coating system was studied. The in vitro cytotoxicity studies were performed on human osteoblast cells MG-63 to observe cell morphology, attachment, proliferation and differentiation. It was found that the silane coated alloy shows an improved corrosion resistance and biocompatibility as compared to bare Mg-6Zn-Ca alloy. Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia.