Graduation Date

Fall 12-14-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Medical Sciences Interdepartmental Area

First Advisor

Geoffrey M. Thiele

Second Advisor

John G. Sharp

Third Advisor

Fereydoon Namavar

Abstract

Past studies have shown that the success of total joint replacements depends on the biocompatibility of orthopaedic materials, which can be improved by modifying the implant surface. However, the exact roles of these modifications and their effective mechanisms are poorly understood. The objective of this study was to develop and evaluate a model system to investigate the impact of nano-structured surfaces, produced by the ion beam-assisted deposition (IBAD) technique, on biomarkers of osteointegration using an in vitro model. The IBAD technique was employed to deposit zirconium oxide (ZrO2), Titanium oxide (TiO2), and Titanium (Ti) nano-films on glass or Ti substrates. Essential cellular functions including adhesion, proliferation, differentiation, and apoptosis of a human osteosarcoma cell line (SAOS-2) were compared on coated vs. uncoated surfaces at both molecular and gene levels.

Our studies have resulted in several novel observations, including enhanced cell adhesion on nano-coated surfaces assessed by the number of DAPI-stained cells along with monitoring cell morphology (actin stress fiber remodeling at focal adhesion sites) on the surfaces using immunofluorescence techniques. Similarly, we reported that IBAD nano-modifications increased cell proliferation on nano-surfaces measured by mitochondrial dehydrogenase activity and a nuclear cell proliferation-associated antigen. Moreover, enhanced cell differentiation on IBAD-produced surfaces was determined by ALP activity and the rate of calcium deposition in alizarin red assays that are in vitro indicators of the successful bone formation. In addition, programmed cell death and necrosis assessed by annexin V staining and flow cytometry observed to be higher on uncoated surfaces compared to nano-surfaces. Finally, there was a correlation between IBAD-modifications and enhanced bone-associated gene expression at cell adhesion, proliferation, and differentiation as assessed by polymerase chain reaction (PCR) techniques.

In summary, our studies using an in vitro model system showed that nano-coated surfaces produced by the IBAD technique are superior to uncoated surfaces in supporting bone-cell adhesion, proliferation, differentiation, and reducing apoptosis at both molecular and gene levels. Therefore, increased osteoblast cellular functions and enhanced bone formation with stronger attachments would be expected from these surfaces in bone-cell applications. In contrast, as anticipated by design, polish uncoated metallic surfaces, e.g., cobalt-chromium inhibited such interactions.

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