COVID-19 Information

PhD Thesis Proposal: Hannah Grover

Thursday, December 3, 2020, 8:30am

Videoconference

For info on how to attend this videoconference, please email hannah.m.grover.TH@dartmouth.edu

“Microstructural and Mechanical Property Characterization of UHMWPE Resin Consolidated Through Equal Channel Angular Processing”

Abstract

Orthopedic devices that can survive more than 20 years in vivo require a bearing surface that can combine toughness, wear resistance, and chemical stability. Ultrahigh molecular weight polyethylene (UHMWPE) remains the gold standard for these bearings, having been utilized as a liner and bearing surface for over five decades. While its wear resistance and mechanical integrity are partially responsible for the success of knee and hip replacements, the material can still fail due to oxidation, fatigue fracture, or adhesive/abrasive wear. Such failures of UHMWPE in orthopedic implants are responsible for almost a third of all revision surgeries. Well-documented material trade-offs leading to these failure modes suggest that hip liners and knee bearing surfaces without optimal processing may be prone to premature failure in the patient. Because the demographic of those receiving implants is changing, implants may need to be tunable to allow optimization for the patient of the future. Most recent work has focused on optimal gamma doses, ideal post-irradiation thermal treatments to reduce oxidation, incorporation of antioxidants, and sterilization/packaging methods. These research avenues do not explore the original microstructure of the material or optimization potential before irradiation.

The present work proposes to change the material trade-offs by attempting to increase the entanglement density of molecular chains. Because entanglements are physical connections and not chemical bonds, chains maintain their mobility to a higher degree than ductility-reducing cross-links. It is theorized that if a high enough entanglement density could be achieved, the anisotropy of articulating surfaces and the generation of wear debris could be prevented in a similar mechanism as carried out by cross-linking. Equal channel angular processing (ECAP) will be used to alter the microstructure through imparted shear. ECAP allows for a homogenous shear process across a plane of the material during which the material maintains the same cross-sectional and length dimensions before and after shear. This method of shearing has been well exploited for metals, but little research has been done on its effect on polymers. Micro-tracers, notably carbon-based conductive.

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.