Chemical characterization of silicon‐substituted hydroxyapatite

Abstract

Bioceramic specimens have been prepared by incorporating a small amount of silicon (0.4 wt %) into the structure of hydroxyapatite [Ca10(PO4)6(OH)2, HA] via an aqueous precipitation reaction to produce a silicon-substituted hydroxyapatite (Si-HA). The results of chemical analysis confirmed the proposed substitution of the silicon (or silicate) ion for the phosphorus (or phosphate) ion in hydroxyapatite. The Si-HA was produced by first preparing a silicon-substituted apatite (Si-Ap) by a precipitation process. A single-phase Si-HA was obtained by heating/calcining the as-prepared Si-Ap to temperatures above 700 degrees C; no secondary phases, such as tricalcium phosphate (TCP), tetracalcium phosphate (TeCP), or calcium oxide (CaO), were observed by X-ray diffraction analysis. Although the X-ray diffraction patterns of Si-HA and stoichiometric HA appeared to be identical, refinement of the diffraction data revealed some small structural differences between the two materials. The silicon substitution in the HA lattice resulted in a small decrease in the a axis and an increase in the c axis of the unit cell. This substitution also caused a decrease in the number of hydroxyl (OH) groups in the unit cell, which was expected from the proposed substitution mechanism. The incorporation of silicon in the HA lattice resulted in an increase in the distortion of the PO4 tetrahedra, indicated by an increase in the distortion index. Analysis of the Si-HA by Fourier transform infrared (FTIR) spectroscopy indicated that although the amount of silicon incorporated into the HA lattice was small, silicon substitution appeared to affect the FTIR spectra of HA, in particular the P-O vibrational bands. The results demonstrate that phase-pure silicon-substituted hydroxyapatite may be prepared using a simple precipitation technique.

Response of osteoblasts and preosteoblasts to calcium deficient and Si substituted hydroxyapatites treated at different temperatures

“…M a n u s c r i p t 5 grafts, several modifications have been proposed such as the preparation of calcium deficient hydroxyapatite (CDHA) [21], low temperature methods [22] and silicon incorporation (Si-HA) [23][24][25] among other strategies. Apatite based bioceramics treated at temperatures below 900ºC result in materials with many microstructural defects (such as high microporosity and incomplete sintering), which show crystallites smaller than 50 nm in size [21,24].…”

Rietveld Refinement of the Crystal Structure of Hydroxyapatite Using X-ray Powder Diffraction

“…The band found at around 875 cm 1 can be characteristic to the ν2 vibration mode and the stretching vibrations of the CO 3 2-group are highlighted by the band in the region 1400 and 1500 cm -1 . The carbonate presence in the specimens is due to absorbance of carbon dioxide from the air during synthesis of the sample and it has been reported by others [23,24].…”

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“…4a and 4b. This peak corresponds to a replacement of phosphate with silicate group in the HA structure 9,13 . A mechanism of this replacement can be described by the following equation 9 : 10 Ca 2+ + (6 − x) PO 3 -4…”

“…For these reasons, there has been interest in synthesizing siliconsubstituted hydroxyapatite (Si-HA). Several methods for the synthesis have been reported including solgel 6 , hydrothermal 7 , solid-state reaction 8 , and chemical precipitation, and crystallization 9,10 . Chemical precipitation and crystallization are the most commonly used methods because they are simple and cheap.…”