Bio-active Calcium Phosphate Thin Films on Implant Grade Titanium Alloy Using a Silica Barrier Layer
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Bio-active Calcium Phosphate Thin Films on Implant Grade Titanium Alloy Using a Silica Barrier Layer J. Reid 1, M. Sayer 1, and T.J.N. Smith 2 1 Department of Physics, Queen's University, Stirling Hall, Queen's Crescent, Kingston, ON K7L 3P6, Canada 2 Millenium Biologix Inc., 785 Midpark Drive, Kingston, ON K7M 7G3, Canada
ABSTRACT Resorbable calcium phosphate (CaP) thin films previously prepared only on quartz substrates were fabricated on Ti-6Al-4V implant grade titanium alloy. In order to maintain the characteristic phase composition and surface morphology of the CaP thin film, an intermediate silica barrier layer was deposited on the titanium alloy via chemical vapour deposition (CVD) using a metal organic precursor. CaP thin films were subsequently deposited on the intermediate SiO2 layer using the dip coating method, and sintered at 1000°C. The final sintered films have a multiphase composition consisting of calcium hydroxyapatite (HA) and a silicon stabilized form of alpha tri-calcium phosphate, or Si-TCP. The thickness of the silica barrier layers were evaluated in terms of the main CVD processing parameters using variable wavelength fixed angle ellipsometry and these parameters were optimized to best reproduce the characteristic CaP thin film. The phase composition and surface morphology of the CaP thin films were characterized using glancing angle X-ray diffraction and scanning electron microscopy. INTRODUCTION In order to improve their biocompatibility, metal alloy implants have been coated with CaP coatings by a wide variety of techniques [1]. A high quality implant coating will ideally participate in stable and prolonged bone integration, while maintaining firm adhesion to the underlying implant. CaP thin films deposited via the dip coating method on quartz and sintered at 1000°C have previously been shown to be resorbable [2]. The unsintered CaP thin films have a composition identical to calcium hydroxyapatite (HA), but during sintering transform to a phase composition of approximately 75% α-TCP, the balance remaining HA. Silicon diffuses from the quartz substrate and stabilizes the α-TCP structure to form silicon stabilized TCP (Si-TCP) previously discussed elsewhere [3, 4]. These films also have a characteristic globular, interconnected surface morphology. The resorptive capability of the thin films is attributed to the characteristic phase composition and surface morphology. These resorbable CaP thin films are known by the trade name OsteologicTM, and are manufactured commercially on quartz by Millenium Biologix Inc.. In order to prepare CaP thin films on metallic substrates, the deposition of a silica barrier layer, which would act as both a source of silicon and a metal ion diffusion barrier, was necessary. In the present study, this was accomplished using a CVD technique.
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EXPERIMENT A two step process was used to replicate OsteologicTM thin films on Ti-6Al-4V alloys. First, a silica barrier layer was deposited on the polished alloy substrate using chemical vapour deposition (CVD). Se
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