Enhanced Osteoblast Adhesion on a Novel Hydroxyapatite Coating
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Enhanced Osteoblast Adhesion on a Novel Hydroxyapatite Coating Michiko Sato, Elliott B. Slamovich, Thomas J. Webster‡ School of Materials Science and Engineering and ‡Department of Biomedical Engineering, Purdue University, West Lafayette, IN 47907 ABSTRACT Plasma spray deposition of hydroxyapatite (HA) onto a titanium implant involves high temperatures that may alter HA crystallinity and induce cracks in the coating. For this reason, the objective of this study was to design a novel HA coating material and method. Titanium was coated with HA, titania, and Poly (dl-lactic-glycolic acid) (PLGA) using sol-gel processing. The biocompatibility of the HA coating in the present study was compared to that of a plasmasprayed HA coating. Results of this study showed that osteoblast adhesion was promoted more in the HA coating proposed in this study than on the plasma-sprayed HA coating. In addition, hydrothermal treatment of the coating appeared to improve the biocompatibility of the HA coating. Since osteoblast adhesion is a necessary requirement for increased bonding of an implant to juxtaposed bone, these results support that hydrothermally sol-gel processed HA may be an optimal implant coating material and method. INTRODUCTION Calcium phosphorous compounds like hydroxyapatite (HA; Ca10(PO4)6OH2) have been used for orthopedic/dental implant applications. HA-coated implants may promote sufficient bone formation directly on juxtaposed bone and firm fixation between the bone and the implant [1]. Many different techniques including plasma spray processing, sol-gel processing, and electrochemical deposition have been proposed to coat titanium with HA. Techniques are desired to produce HA coatings which have few cracks and exceptional biocompatibility properties. Although plasma spray deposition is a widely used technique, it is performed at high temperatures resulting in multiple phases and lower crystallinity HA [2]. It has been reported that the dissolution rate of HA increases with decreasing crystallinity [3], and that other calcium phosphorous compounds dissolve faster than HA [4]. Compared to plasma spray, sol-gel processing can attain a more uniform composition and surface morphology with fewer cracks. Sol-gel processing is also suitable to coat complex shapes [5]. For these reasons, the objective of this study was to use a novel HA coating technique based on sol-gel processing, and evaluate its cytocompatibility relative to conventional plasma-sprayed HA coatings. EXPERIMETAL PROCEDURES Materials preparation 0.6 M ammonium phosphate solution (Sigma) was added to dH2O and then was adjusted to a pH of 10 using ammonium hydroxide (Fisher Scientific, Inc.). 1 M calcium nitrate solution (Sigma) was then added dropwise to the ammonium phosphate solution at a rate of 18 ml/min with stirring. HA started to precipitate as soon as the calcium nitrate solution was added. The solution was stirred for 24hrs at room temperature. After that time period, the HA precipitates
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