Bioactivity of Vitronectin Adsorbed on Nanophase Alumina Promotes Osteoblast Adhesion
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Bioactivity of Vitronectin Adsorbed on Nanophase Alumina Promotes Osteoblast Adhesion Thomas J. Webster1,3, Linda S. Schalder2, Richard W. Siegel2, Rena Bizios1 Departments of 1Biomedical Engineering and 2Materials Science and Engineering Rensselaer Polytechnic Institute, Troy, NY 12180-3590, U.S.A. 3 Present address: Department of Biomedical Engineering Purdue University, West Lafayette, IN 47907-1296, U.S.A.
ABSTRACT The role of the conformation and bioactivity of adsorbed vitronectin in enhancing osteoblast (the bone-forming cells) adhesion on nanophase (that is, grain sizes less than 100 nm) alumina was investigated in the present in vitro study. Results obtained from surface-enhanced Raman scattering (SERS) provided the first evidence of increased unfolding of vitronectin adsorbed on nanophase alumina. This conclusion was further supported by dose-dependent inhibition of cell adhesion on nanophase alumina pretreated with vitronectin following preincubation of osteoblasts with either Arginine-Glycine-Aspartic Acid-Serine (RGDS) or Lysine-Arginine-Serine-Arginine (KRSR) to block respective cell-membrane receptors. These events, namely enhanced unfolding of vitronectin that leads to exposure of bioactive epitopes (such as RGDS) in adsorbed vitronectin may explain the observed increased osteoblast adhesion on nanophase alumina. INTRODUCTION Recent in vitro studies provided evidence of increased osteoblast (the bone-forming cells) adhesion on nanophase (i.e., those with grain sizes less than 100 nm) compared to larger conventional grain size alumina1-5, titania2,4, and hydroxyapatite2,4. Such studies demonstrated that enhanced osteoblast adhesion was independent of ceramic surface chemistry and material phase, but was dependent on the surface topography of nanophase ceramics4. The mechanism(s) of enhanced osteoblast adhesion on the novel nanoceramic material formulations have yet to be fully investigated and understood. It is known, though, that cell adhesion involves proteins since, in the absence of serum, osteoblast adhesion was greatly reduced and independent of nanoceramic grain size4. Furthermore, it has been established that vitronectin plays a crucial role in this process since osteoblast adhesion was greatly enhanced on nanophase ceramics pretreated with vitronectin compared to other proteins contained in serum (such as albumin, laminin, fibronectin, and collagen)4. Lastly, protein adsorption experiments provided evidence of greater amounts of calcium-mediated vitronectin adsorption on nanophase compared to larger conventional grain size ceramics5. These studies established the importance of vitronectin in mediating osteoblast adhesion on nanophase ceramics. The present project sought to elucidate the role that the conformation and bioactivity of vitronectin adsorbed on nanophase ceramics play in the process of mediating enhanced osteoblast adhesion.
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MATERIALS AND METHODS Ceramic Synthesis and Preparation Alumina (Al2O3) samples (discs 10 mm in diameter and 2 mm thick) were prepared as previousl
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