Journal
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A
Volume 64A, Issue 4, Pages 655-663Publisher
WILEY-LISS
DOI: 10.1002/jbm.a.10330
Keywords
calcium phosphate phases; hydroxyapatite; amorphous calcium phosphate; electrochemistry; titanium
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An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca2+/HxPO4(3-x)-)-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36degreesC). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (similar to30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology. (C) 2003 Wiley Periodicals, Inc.
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