In vitro study of electron beam deposited calcium phosphate coating in simulated body fluid
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Ari Ide-Ektessabi International Innovation Center, Kyoto University, Sakyo-ku, 606-850 Kyoto, Japan
J.A. Toque Department of Engineering Design and Manufacture, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia (Received 2 February 2006; accepted 4 October 2006)
Calcium phosphate coatings prepared using the technique of electron beam deposition were immersed in a simulated body fluid for different periods of time to determine their response in vitro. The amorphous as-deposited coatings dissolved completely after a few days of immersion. After annealing in air at 700 °C, the dissolution of a small amount of amorphous phase in the crystalline coatings promotes the precipitation of bonelike apatite on the recessed regions by increasing the local supersaturation of calcium and phosphate ions. Formation of apatite was confirmed by the x-ray diffraction peaks at (200), (211), and (203) planes which grew after immersion in simulated body fluid. Fourier transform infrared results conformed to this with the increase in intensity of the absorption band at 1450 cm−1, signifying the increase in carbonate content. Scanning electron microscopy results showed spherical-shaped apatite nucleated on dissolved surface after 8 days of immersion. Sixteen days after immersion, almost 80% of the surface area was covered with apatite formation and grew to coalesce between neighboring particles forming an integrated platelike layer after 28 days. No obvious detachment between the grown layer and the underlying coating was observed.
I. INTRODUCTION
Calcium phosphate compounds have been applied in various ways as implant materials for bone substitution and repair. The response and behavior of these biomaterials in biological environments is crucial for their use in vivo. The bioactivity of CaP and many other materials has been related to their natural tendency to nucleate carbonate crystals analogous to bone minerals. In the case of hard tissue replacements, direct bone apposition to implants is essential to assure the stability of the implant clinically. Hydroxyapatite (HAp) is one of the biomaterials that forms a chemical bond to bone. Because of its low strength and low fracture toughness, HAp is often used as a thin coating layer on a metallic substrate to enhance the retention of an implant by direct bone bonding. It is reported that HAp contributes not only to the formation of a strong bond to the bone, but
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0075 J. Mater. Res., Vol. 22, No. 3, Mar 2007
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also early bone formation around the implant.1,2 The formation of biological apatite on the surface of implanted synthetic CaP ceramics through a sequence of chemical reactions may be one of the events leading to bonding with bone.3–6 Hyakuna et al. reported that the precipitation rate in a simulated body fluid (SBF) appears to correlate with the dissolution rate of bioactive ceramics in vitro.7 To reveal the m
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