Effect of Metal Substrate Nanometer Topography on Osteoblast Metabolic Activities

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Effect of Metal Substrate Nanometer Topography on Osteoblast Metabolic Activities Brian C. Ward1 and Thomas J. Webster2 1 School of Chemical Engineering 2 Department of Biomedical Engineering and School of Materials Engineering Purdue University West Lafayette, IN 47906 ABSTRACT Surgeons and bioengineers have continuously been challenged by implant failure. Many of these engineers and surgeons trace implant failure to poor osseointegration (the bonding of an orthopedic implant to juxtaposed bone) and to the inability of implants to match the physical properties of surrounding bone. Researchers have recently shown that nanostructured materials (or materials with fundamental length scales less than 100 nm) enhance cell functions pertinent to effectively regenerating the tissue of numerous organs. Specifically, in a recent study, researchers demonstrated that metal surfaces utilizing low-micron to nanophase topography fostered increased adhesion of osteoblasts, the cells that create the matrix of bone. In this study, Ti, Ti6Al4V, and CoCrMo alloys were investigated, and these alloys were identical to current orthopedic implant alloys except for surface topography. The objective of this in vitro research was to determine whether these same nanophase metal surfaces not only foster osteoblast adhesion but also increase osteoblast metabolic activities leading to bone regeneration. Light microscopy and Energy Dispersion Spectroscopy (EDS) were used to verify the presence of calcium and phosphorous deposition by osteoblasts cultured on the metal substrates. Results indicated that both calcium and phosphorous are being deposited on several of the metal substrates. More importantly, compared to conventional metals, results provided the first evidence that more calcium and phosphorous was deposited by osteoblasts cultured on respective nanophase metals (Ti, Ti6Al4V, and CoCrMo). Nanophase CoCrMo had the most calcium and phosphorous minerals deposited by osteoblasts compared to any other metal substrate. Thus, the results of this study continue to provide evidence for the use of nanophase metals for the design of the next generation of more successful orthopedic implants. INTRODUCTION Implant failure has challenged orthopedic surgeons and bioengineers for numerous decades. Many of these engineers and surgeons trace implant failure to poor osseointegration, the bonding of an orthopedic implant to juxtaposed bone, and to the inability of implants to match the physical properties of surrounding bone [1-3]. For instance, immature bone has an average inorganic mineral grain size of 10-50 nm; mature bone has an average inorganic mineral grain size of 20-50 nm and is 2-5 nm in diameter [3]. However, most modern implants are smooth at the nanometer level since they are composed of constituent micron grain sizes [3]. Importantly, researchers have shown that nanostructured materials (including ceramics, polymers, and composites thereof) enhance cell function [4-11]. Specifically, in a recent study, researchers demonstrated that m