Date of Award

5-1-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Jeremy L. Gilbert

Keywords

Composite, Corrosion, Medical Device, PEEK, Polyethylene, Taper

Subject Categories

Engineering

Abstract

Novel methods for assessing the electrochemical and micromechanical performance of modular tapers were evaluated, and self-reinforced composite materials were developed for their potential to prevent the onset of mechanically assisted corrosion in modular taper devices.

A study of the seating and taper locking mechanics of modular taper samples was conducted, and the effect on taper engagement strength of seating load, loading rate, taper moisture, and taper design/material combination was studied. The load-displacement behavior was captured during seating, and the subsequent pull off load was correlated to seating displacement, seating energy, and seating load. The primary factor affecting taper engagement strength was seating load, and loading rate and design/material factors did not have a significant impact on the quality of the taper engagement.

Next, the effect of variation of 7 different design, material, and surgical factors on the fretting corrosion and micromechanical behavior during incremental cyclic fretting corrosion testing was examined using a design of experiments matrix. Seating load and head offset length were the most influential factors affecting fretting corrosion, with low seating loads and high head offsets giving rise to increased currents during sequentially incremented cyclic loads.

Poly(ether ether ketone) (PEEK) fibers were produced, and the effects of varying draw down ratio, molecular weight, and post-spinning treatment on the structural and mechanical properties of the fibers were studied. Highly drawn fibers showed the highest increase in molecular orientation and mechanical properties. PEEK fibers were then utilized in the design and fabrication of self-reinforced composite PEEK (SRC-PEEK) thin film composites, and self-reinforced composite ultra-high molecular weight polyethylene (SRC-PE) produced from Spectra fiber was also introduced. Pin on disk studies were employed to understand the potential of both of these SRC materials to effectively insulate CoCrMo/Ti6Al4V alloy interfaces during cyclic fretting motion at contact stresses similar to those that might be experienced in modular taper junctions. SRC-PEEK and SRC-PE reduced fretting currents by approximately two orders of magnitude as compared to metal-metal interfaces, and sliding mechanics for SRC-PEEK lined samples were similar to metal-metal interfaces, while SRC-PE samples created a much lower COF at the interface.

Finally, SRC-PEEK and SRC-PE gaskets were created to sleeve the trunnions of modular tapers and insulate the head from the trunnion. Cyclic fretting corrosion techniques were employed to assess the ability of SRCs to reduce or prevent the onset of fretting corrosion in the modular taper junction. In a set of three short-term tests assessing the effects of incremented cyclic loads, frequencies, and working electrode potential, SRC lined samples prevented the onset of fretting corrosion and had significantly lower currents than severely corroding metal-metal samples. In long-term million cycle cyclic fretting corrosion testing, the SRC gaskets did not experience failure at any point throughout the test and did not allow for the onset of corrosion currents. Inspection of the gaskets following all testing confirmed that the SRC gaskets withstood the high contact stresses and abrasive fretting motion experienced during the cyclic tests performed, indicating that SRC-PEEK and SRC-PE may be suitable candidates as new materials to prevent the onset of fretting corrosion in modular taper junctions.

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