Directed Osteoblast Adhesion at Particle Boundaries: Promises for Nanophase Metals
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Directed Osteoblast Adhesion at Particle Boundaries: Promises for Nanophase Metals Venu Perla1, Jeremiah U. Ejiofor1, and Thomas J. Webster1,2 1 Department of Biomedical Engineering and 2School of Materials Engineering Purdue University 500 Central Drive West Lafayette, IN 47907-2022, U.S.A. ABSTRACT In spite of under performance, metals and metal alloys are currently being used in orthopedic implantable devices. Poor osseointegration, severe stress shielding, bone cell death and eventual necrotic bone resulting from the generation of wear debris are known to be some of the reasons responsible for their under performance. In addition, metallic corrosion products may also initiate cancer. Steady growth in the use of metals in orthopedic applications inspired researchers to deal with these problems in an integrated way. When conventional Ti, Ti6Al4V, and CoCrMo surfaces were modified to the nano-range, this study showed increased percentages of osteoblast (bone forming cell) adhesion on nanophase metals. Moreover, larger amounts of osteoblast adhesion was related to quantitative increases in the total length of particle boundaries per unit area and the total number of pores between surface particles per unit area, and the surface particle boundary index (SPBI) of nanophase metals. Additionally, we have developed a novel anticarcinogenic orthopedic metalloid, selenium (Se). When micron range surface particles of Se compacts were modified to the nano-range by chemical etching, we found positive relationships between directed osteoblast adhesion and various particle boundary parameters mentioned above under in vitro conditions. These results provided the first evidence to utilize nanosurface Se as an anticarcinogenic and bio-inspiring material for future applications in orthopedic metallic devices. INTRODUCTION Approximately 245,000 U.S. citizens each year have a total knee or hip replaced using implants that are composites of metal, polymers, and ceramics. Ti alloys and CoCrMo alloys are commonly used in these orthopedic implant materials. Steady growth in the number of joint replacements is expected over the next decade [1]. However, under performance of these implants are attributed to: (i) incomplete osseointegration (i.e., lack of bonding of an orthopedic implant to juxtaposed bone) between surrounding bone and the prostheses [2-5], (ii) severe stress shielding [3-5] due to significant differences in mechanical properties between an implant and surrounding bone, and (iii) the generation of wear debris at articulating surfaces of orthopedic implants that may lead to bone cell death and perhaps eventual necrotic bone [4, 5]. Although, metal alloys are routinely used in orthopedic implant devices, metals such as Ti are alien elements in the physiology. The literature [6] indicates that these are not essential elements to human health. Metal alloys like CoCrMo or Ti6Al4V are known to under go corrosion under in vivo conditions [7]. The continuous exposure of tissue to metallic corrosion products is considered
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