Author ORCID Identifier

https://orcid.org/0000-0002-2688-8453

Date of Award

2025

Document Type

Thesis (Ph.D.)

Department or Program

Engineering Sciences

First Advisor

Douglas W. Van Citters

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is a linear long chain homopolymer valued for its toughness, wear resistance, and chemical inertness. In the medical field, these properties make it the material of choice for bearing surfaces despite recognized tradeoffs between wear resistance, toughness, and oxidation resistance. Electrically conductive composites of UHMWPE show promise to enable new types of smart and active load-bearing implants in a future of personalized medicine, if beneficial properties can be maintained with the addition of solid-state additives.

Clinical need-finding conducted through Dartmouth’s Training Program in Surgical Innovation revealed several potential applications for conductive, load-bearing polymers. These include: (1) conductive knee bearings for electrochemical treatment of prosthetic joint infection, (2) strain sensors for arthroplasty and spinal applications, and (3) electrodes for embedded sensors in orthopedic bearings. Each application area demands specific material properties, requiring a framework for producing a tough, conductive polymer composite with adjustable parameters while considering property tradeoffs.

Carbon black nanoparticles were added to UHMWPE to confer conductive properties while providing good interphase adhesion. A range of carbon black concentrations were tested to understand the effect of additive concentration on certain mechanical and electrical properties relevant to highly-loaded applications. Mechanical toughness measures indicated that tensile and impact toughness properties were more affected by the presence of the additive than fatigue properties. Comparisons to neat void-filled materials demonstrated that this effect could be explained in part by the presence of intergranular defects in the material. Electrical results demonstrated that resistive properties were predictable in the plastic regime at lower strains, but deviated from theoretical behaviors at higher strains. These results provided a key understanding of the deformation behavior of conductive nanoparticles in these materials. Furthermore, results showed that these composites can simultaneously meet mechanical and electrical requirements for the applications of interest. Overall, this work demonstrated mechanical and electrical viability of these materials for clinical applications while providing a deeper understanding of structure-property relationships in solid-state, electrically conductive composites of UHMWPE.

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