The research objective of this award is to test the hypothesis that superior surface integrity enables a significant increase of corrosion resistance of novel biodegradable orthopedic magnesium-calcium implants. The research approach is to adjust surface integrity of magnesium-calcium implants by a new hybrid dry cutting-finish burnishing process. The specific methodology includes: (1) fabrication of biodegradable, biocompatible, and lightweight magnesium calcium alloys via calcium alloying and characterization of dynamic mechanical behaviors and microstructures, (2) creation of desired surface integrity of implants through the novel hybrid dry cutting-finish burnishing process with acoustic emission process monitoring, (3) development of a microscale finite element analysis model to provide a fundamental understanding on the process mechanics and surface integrity, and (4) characterization of process-induced surface integrity and its effect on biodegradation performance in simulated body fluids.
The research results will enable progress in biodegradable orthopedic implants via solving the pressing issues of stress shielding and surgical interventions associated with commercial permanent metallic implants. It will provide an insight into the basic relationships between process parameters, surface integrity, and biodegradation performance of orthopedic implants. The benefits to society include the improved life quality and reduced financial burden of the affected individuals. The socioeconomic benefits of biodegradable magnesium-calcium implants will also help boost the competitiveness of the booming medical device manufacturing industry.
Intellectual Merits: This project aims to manufacture biodegradable magnesium calcium (MgCa) orthopedic implants with controllable corrosion performance through adjusting surface integrity by a novel hybrid dry cutting – finish burnishing process. A synergistic experimental, theoretical, and numerical study has been conducted, specifically: Fabricated biodegradable, biocompatible, and lightweight magnesium calcium (MgCa) alloys via calcium alloying to increase the corrosion resistance. Determined dynamic mechanical behaviors and microstructures of the MgCa alloys. Created an efficient hybrid dry cutting – finish burnishing process with acoustic emission (AE) monitoring to produce desired surface integrity of MgCa implants, and developed a microscale finite element analysis model to provide a fundamental understanding of burnishing process mechanics. Characterized the process-induced surface integrity including surface finish, residual stress, microstructure, and microhardness, and established the basic relationship between burnishing pressure, surface integrity, and AE monitoring signals. Evaluated and characterized the effect of process-induced surface integrity on biodegradation performance via corrosion of MgCa Implants in a simulated body fluid. The completed research has made several unique technical contributions including: (a) an enabling calcium alloying technique to increase corrosion resistance, stabilize corrosion rate, and enhance mechanical property of the MgCa implants; (b) a new hybrid synergistic dry cutting – finish burnishing process and simulation methodology to significantly enhance implant surface integrity which is a key for increasing corrosion resistance; and (c) a fundamental linkage between process parameters, surface integrity, and corrosion performance. Broader Impact: On the socioeconomic end, the use of MgCa implants will make biodegradable implants a viable therapeutic modality in the 21st century, improve the quality of life of the affected individuals, and make them more productive while help lifting a financial burden on the US health care system. The collective advantages of biodegradable MgCa implants will also substantially boost the competitiveness of booming US medical device manufacturing industry via broad knowledge dissemination (26 publications and 21 seminars), strong industrial consortium (2 industrial collaborators), working groups of professional societies, research collaborations, and various outreach mechanisms. The transformative research provides an example of paradigm transition to high value-added medical device manufacturing.
