Corrosion and Biocompatibility of Traditional and Next Generation Metallic Orthopaedic Biomaterials
Brooks, Emily K.
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Both traditional bioinert materials, as well as next generation bioactive materials, are intended to replace or repair damaged tissue within the body following their implantation. For each material, it must be considered how the biological environment will affect the performance of the biomaterial, as well as how the presence of a foreign material will affect the surrounding biology. The initial goal of the work was to characterize the impact of a simulated inflammatory response on the electrochemical behavior of traditional metallic orthopaedic biomaterials. The investigated materials, all materials presently employed in orthopaedics due to their known corrosion resistance, included commercially pure titanium (cpTi), titanium-6%aluminum-4%vanadium (Ti64), and 316L stainless steel. Inflammatory conditions significantly reduced the corrosion resistance of the examined materials, with the alloys experiencing more pronounced changes. This was followed by examination of a next generation biodegradable metallic material, magnesium (Mg) alloy magnesium-9%aluminum-1%zinc (AZ91), exposed to a simulated inflammatory environment. Again, it was determined that a simulated inflammatory environment initiated increased corrosion processes of the Mg alloy. The interaction of AZ91 with both eukaryotic and prokaryotic cells was then characterized. Cells were able to adhere to and grow on the corroding AZ91 material surface, and it was observed that the corrosion rate of the material was modified as a function of the cellular coverage. Bactericidal material properties were demonstrated for AZ91 through in vitro testing, but were absent in in vivo testing. A broad characterization of the corrosion resistance of three additional next generation Mg alloys was then completed, demonstrating that low alloying additions of various biocompatible elements are feasible. Preliminary antimicrobial studies on a select alloy, magnesium-2%strontium (Mg2Sr), were performed; however, the Mg alloy showed no bactericidal effects in vitro or in vivo. Overall, the presented work displays the importance of understanding the dynamic relationship between a material and the surrounding biology. Material behavior and the biological response are interdependent, and properly assessing their relationship is crucial to ensure biomaterials function as intended.