Date of Award

Spring 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Sankar, Jagannathan

Abstract

There is a need for innovation in medical implant devices through novel biomaterials that will improve the quality of life. The first step in the creation of a foundation of knowledge and technology to improve these implant devices is through the creation of new alloys with the capabilities of biodegradation and bioabsorption without a toxic effect that will pass through FDA regulatory procedures. In this study, unique heat treatment processing techniques coupled with innovation in elemental alloying produced distinctive magnesium (Mg) based alloy systems. The MgZnCa system was used as the underpinning system where four groups of novel alloys were developed, which include the as-cast Mg−xZn−0.3Ca system, the heat treated Mg−4.0Zn−0.3Ca system and as-cast and heat treated Mg−1.0Zn−0.3Ca system alloyed with 1.3% rare earth elements. All alloy groups were assessed through immersion corrosion tests utilizing 0.9% NaCl physiological solution and MEMα cell culture medium, tensile and compressive mechanical testing, and cytotoxicity assays. The increase of Zn content in the Mg−xZn−0.3Ca system had an effect on phase precipitation and grain size refinement, which caused an increase in mechanical strength and a reduction of corrosion resistance up to a Zn content of 4.0 wt.%. The cytotoxicity assays determined that the Mg−4.0Zn−0.3Ca system showed negative cytocompatibility with the MC3T3-E1 cell line which can be reduced or eliminated by diluting the interaction between the two. The addition of rare earth elements caused significant grain size refinement, increased corrosion resistance, increased mechanical strength compared to the MgZnCa system, and positive cytocompatibility. Through this research, novel Mg-based alloys were developed with the potential of being employed as orthopaedic biomaterials capable of supporting the mechanical and physical function of an injured tissue throughout the entire healing process.

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