MTech (Research) Colloquium: Mr. Lochan Upadhyay (22/09/23)
Thesis title:
Effect of Processing Mg-6Zn-0.2Ce through High-Pressure Torsion on Its Use as a Biomaterial
Faculty advisor(s):
Prof. Praveen Kumar and Prof. Kaushik Chatterjee
When?
22nd September, 2023 (Friday), 03:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract:
Conventionally, internal fixation devices that help fractured bone for conventional osteosynthesis are made of titanium alloys and stainless steel. As they are non-degradable, their removal requires revision surgery, which is expensive and patient unfriendly. As an alternative, Mg-based biomaterials are being actively explored as bioresorbable implants. The low Young’s modulus of Mg also helps to minimize stress shielding. However, the high corrosion rate and low strength limit its clinical application. In practice, severe plastic deformation (SPD) can significantly improve mechanical properties; however, the effect of SPD processing on Mg-based biomaterials is not well understood. This work aimed to study the effect of processing Mg-6Zn-.2Ce alloy by high-pressure torsion (HPT). Samples were processed using 6 GPa pressure for 1, 2, or 5 turns. Tensile tests using sub-standard samples, machined from HPT-processed disks, were performed using a micro-mechanical tester, and the 2D strain field was accurately measured using digital image correlation. An in vitro study was performed to assess its cytocompatibility. Critical assessment of corrosion was performed using both electrochemical analysis and immersion method. Two-turn HPT samples exhibited a five-fold increment in yield strength compared to the annealed, coarse-grained sample, with about a 50 % reduction in ductility. This increment in strength is consistent with the HPT-induced grain refinement from ≈300 µm to ≈50 nm after two turns of HPT. The two-hour open circuit potential (OCP) in stimulated bodily fluid (SBF) showed potential shifts toward the noble direction. Two-turn HPT samples also exhibited the lowest corrosion rate in the two-hour immersion test. An immersion test in SBF for three days revealed a high corrosion rate; however, the corrosion rates of all HPT-processed samples were similar and slightly lower than that of the annealed sample. Finally, cytotoxicity was evaluated by the indirect cell culture method, which showed good biocompatibility, with an insignificant change in cytotoxicity after HPT processing. Notably, the number of cells grew significantly from 1 to 3 days, suggesting good proliferation. In summary, HPT processing to lesser turns demonstrates significant potential for enhancing the suitability of Mg-6Zn-0.2Ce alloy for bioresorbable implants. It offers significantly increased strength, favorable corrosion resistance, and biocompatibility, thus addressing some of the key limitations of conventional fixation devices.