Electron microscopic investigation of interfaces in materials for orthopedic applications
Author(s)Benezra, Valarie Ilene, 1971-
Linn W. Hobbs.
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About 250,000 people undergo knee and hip arthroplasty each year in North America alone, with hundreds of thousands more receiving joints over the rest of the world. Two factors are key to the success of these implants: first, the quality of attachment of the prosthetic joint to the patient's bone, and second, the low generation of wear particles as the components of the prosthesis articulate against each other. This thesis is a study of both of these factors. First, the mechanism of bone apposition to hydroxyapatite (HA) coatings on Ti-6Al-4V was investigated via transmission electron microscopy (TEM). In this section of the study, Ti alloy cylinders were coated with HA by two different methods to yield three types of coatings - annealed and unannealed plasma-spray (PSHA) coatings and an annealed ion-beam assisted deposited (IBAD-HA) coating. These cylinders were implanted in trabecular bone in dogs from periods ranging from 3 hours to 14 days. Mechanical testing indicated that the bone/implant interface with the PSHA coated implants was significantly stronger than that with the IBAD-HA coated or uncoated Ti alloy implants. However, there were no differences in the degree of bone apposition to the three HA-coated materials; thus indicating that bone apposition is not a sufficient indicator of mechanical integrity of the bone/HA interface. In the second section of this study, the microstructural factors contributing to the observed wear properties of the oxide on Zr-2.5Nb were investigated via TEM. Zr-2.5Nb barstock which had been rotary-forged to impart an anisotropic microstructure was sectioned and oxidized in dry air at 600°C and 635°C for a variety of times ranging from 30 minutes to 40 hours. Cross-sections across the oxide/metal interface were observed via TEM. The oxide scale comprises primarily monoclinic zirconia, with small amounts of tetragonal zirconia. Evidence of a mixed oxide phase, 6Zr02.Nb205, was also observed. The microstructure of this oxide is dependent on oxidation temperature, the microstructure of the underlying metal, and oxide depth. Two oxide microstructures originating from beta-Zr grains in the alloy were also identified. A third study concerned the architecture and microstructure of naturally-derived and synthetic bone substitute materials (BSMs). While BSMs are used clinically to promote healing in large bone defects, they were useful to this study as a control for the organization of mineral in mature bone. Low voltage high resolution scanning electron microscopy (LVHRSEM) enabled observations of the three dimensional architecture of these materials which were then correlated with TEM observations. The crystallites in an anorganic bovine-derived BSM were organized in a hierarchical fashion which paralleled the organization of collagen. In contrast, the synthetic materials were organized in an isotropic network. The difference in organization was attributed to the formation of the mineral matrix of bone on an anisotropic collagen template.
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaves 214-230).
DepartmentMassachusetts Institute of Technology. Dept. of Materials Science and Engineering
Massachusetts Institute of Technology
Materials Science and Engineering