Date of Award

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioengineering

Committee Member

Dr. Jeremy L. Gilbert, Committee Chair

Committee Member

Dr. Melinda Harman

Committee Member

Dr. Martine LaBerge

Committee Member

Dr. Guigen Zhang

Abstract

The current paradigm in metallic biomaterials research has focused on biological reactions to wear particles and the cascade by which these reactions contribute to adverse local tissue reactions, including implant loosening and pseudotumors. Conversely, in the body, leukocytes can produce an array of reactive oxygen species (ROS) which may alter the balance of oxidation and reduction reactions occurring at the surface of the metallic implant, thereby accelerating corrosion and causing influx of bioactive corrosion products into the adjacent tissue. Evidence of severe, localized corrosion damage of orthopedic implants has been documented on retrieved (failed) implants, but remain unable to be replicated in laboratory testing in biologically relevant models. The goals of this dissertation are to explore the hypothesis that ROS-based solution chemistry will significantly affect the corrosion and tribocorrosion behavior of CoCrMo alloys and to attempt to recapitulate the corrosion, tribocorrosion or other surface damage mechanisms observed on retrieved hip replacements. In addition, the interaction of metallic implant surfaces, cathodic potentials and cellular processes of immune-based cells in vitro were investigated. This work addresses the specific inflammatory specie hypochlorous acid (HOCl), produced by neutrophils, and its effect on the electrochemical and mechanical performance of orthopedic alloys. Electrochemical and impedance testing of CoCrMo alloy (ASTM-F1537) in HOCl solutions revealed dramatic alterations in the oxide performance of CoCrMo alloy surfaces as well as increases in corrosion currents of up to 3 orders of magnitude and open circuit potential to over 600 mV (vs. Ag/AgCl) in 30 mM HOCl solutions generating significant surface damage. Tribocorrosion tests in a pin-on-disk configuration, and head-neck taper junction fretting corrosion tests both showed up to 5-fold increases in fretting currents in 5 mM HOCl solutions. In in-vitro cell experiments, HOCl was produced by neutrophils in a mixed-cell population in response to cathodically biased Co-Cr-Mo samples, generating 40.8 µmols HOCl over 2 hours in response to an applied potential of -1 V (vs. Ag/AgCl) which is a potential achievable during tribocorrosion processes. In addition to HOCl damage, a standard surgical technique, electrosurgery, which relies on high voltage alternating currents, was shown to cause damage to orthopedic alloy disks, reproducing some damage found on retrieved implants. This observation demonstrates that this common surgical method may have significant deleterious effects on the implant surfaces structure and properties. In this work, HOCl has been shown to affect the tribocorrosion behavior of orthopedic alloys and provides a potential model system of localized inflammation. Furthermore, the corrosion products caused by HOCl and electrosurgery damage could activate an aggressive immune response leading to local tissue damage.

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