My current research projects are in the area of biomaterials- materials that are used in the human body to recover or enhance function. Metal alloys, plastics, and animal-derived materials are currently used in a variety of applications from artificial joints to new heart valves to new lenses for the eyes.
Polyethylene in Joint Prostheses
Ultrahigh molecular weight polyethylene (UHMWPE) is a major component in large human joint prostheses. It is well suited to play the role of cartilage in these devices due to its excellent biocompatibility and high values of many relevant mechanical properties. One of the key problems associated with use of UHMWPE in prostheses is the release of microscopic polymer particles (wear particles) during use, which can lead to adverse biological reactions such as osteolysis. Although treatments such as gamma-irradiation-induced cross-linking have been developed to reduce wear particle production, very little is known about how these treatments affect the microscopic structure, which is fundamentally related to mechanical properties. We use transmission electron microscopy (TEM) or atomic force microscopy (AFM) to visualize the microstructure of UHMWPE. The polymer chains are ordered and stacked into long, worm-like lamellae which give the material crystalline properties (image above). Between lamella, the chains are randomly oriented, which imparts amorphous (glass-like) qualities to UHMWPE. Our laboratory has developed new analysis techniques that allow a quantification of microstructural parameters, which can be correlated to performance properties of the material.
Biological Interactions and Modification of Implant Alloys
The biological environment inside the human body is a chemically active and corrosive one, and corrosion of metalic alloys that are part of implants in the body releases metal ions into the bloodstream. This can cause toxic, immunological inflammation reactions. Fortunately, most metallic alloys naturally form a protective oxide layer at their surface, and this layer resists corrosion to some extent. The nature and evolution of this corrosion resistance for implant alloys exposed to cellular media is currently being investigated. The attachment of cells to the metal surface, a natural occurrence when these devices are placed in the biological environment, causes structural and chemical changes to the metal surface. These changes alter the protective oxide layer and therefore the ability of the metal to resist corrosion. A change in the corrosion properties of the metal may then affect the ability of cells to attach to the metallic surface. Thus, the corrosion of the metal is somewhat manipulated by the external environment, but at the same time the environment is influenced by the corrosion. We are investigated corrosion of titanium and stainless steel as a function of cell attachment and biological environment, with the aim of providing a better understanding of tissue attachment on metallic implant components, which is necessary in the pursuit of longer-lasting and better-performing implants. The image at the right shows the components of a typical hip implant.
I am very grateful to the many students who have worked with me on various research projects (names in boldface are co-authors on refereed publications):
Claire DelBove ′11 - ultra-high molecular weight polyethylene wear particles
Justin Hugon ′09 - ultra-high molecular weight polyethylene wear particles
Drew Scott ’07 - ultra-high molecular weight polyethylene structure
Matt Shanks ’04 - cross-linking in ultra-high molecular weight polyethylene
Sean McKenna ’04 – characterization of CuO nanoparticles
Karyn Spence ’03- ultra-high molecular weight polyethylene characterization
Neil Fore ’03 - ultra-high molecular weight polyethylene structure
Ben Evans ’03 – ultra-high molecular weight polyethylene characterization
Lauren Glas ’03 – rf generator fabrication of alloys
Julia Auwarter ′01 - modification of bone cement with hydroxy apatite