Abstract
Nanosized hydroxyapatite with silicon substitution Ca10(PO4)6−x(SiO4)x(OH)2−x□x (0 ≤ x ≤ 2) of same silicon concentrations, variation of pH and the method of inverse and direct synthesis were successfully prepared first time by the theoretical maximum of incorporation of Si into the hexagonal apatite structure by precipitation method aqueous. The effects of the Si substitution on crystallite size, particle size and morphology of the powders were investigated. The crystalline phase, microstructure, morphology and particle size of hydroxyapatite and silicon substituted hydroxyapatites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), EDX coupled with SEM and transmission electron microscopy (TEM).The samples were successfully synthesized as a single-phase apatite, and crystallization of apatite was enhanced during heating. The results obtained in this study show that the kinetics between different direct and inverse process showed different reactivities, in the presence of varying pH. Compared with the two methods, the inverse method have higher kinetic in the formation of hydroxyapatite silicate because of the difference in lattice parameters. The grain size of Si-HA samples is clearly finer than that of pure HA sample and this decreases with increasing Si content. The growth of HA nanorods with temperature can be described by “oriented attachment”. According to this theory the adjacent HA crystallites would coalesce in one particular direction on the (1 1 0) high energy planes, creating templates to form elongated rod-like structure. Fourier Transform Infrared Spectroscopy analysis reveals, the silicon incorporation to hydroxyapatite lattice occurs via substitution of silicate groups for phosphate groups. Substitution of phosphate group by silicate in the apatite structure results in a increase in the lattice parameters in both a-axis and c-axis of the unit cell.
Highlights
Hydroxyapatite (HA, Ca10(PO4)6(OH)2) ceramics, the major component of human hard tissues[1], are widely used for bone substitutes in orthopedic and dental clinics in the forms of granules, porous or solid bodies, and finer particles [2], due to its excellent biocompatibility and ability to form a direct chemical bond with hard tissues [3] and [4]
After heat treatment at 450 °C for 20 h, pure HA and silicon-containing hydroxyapatite (Si-HA) a different were formed, no secondary phases are detected (Fig. 2). Comparison of these two figures reveals a considerable improvement of the crystallinity and microstrain in the heat-treated material, as it is shown by the diffraction peaks profile and decrease of the full-width at half-maximum
It can be seen that the lattice parameters of Si-HA of All the powders synthesized by the inverse method showed relatively higher than that of by the direct method
Summary
Hydroxyapatite (HA, Ca10(PO4)6(OH)2) ceramics, the major component of human hard tissues[1], are widely used for bone substitutes in orthopedic and dental clinics in the forms of granules, porous or solid bodies, and finer particles [2], due to its excellent biocompatibility and ability to form a direct chemical bond with hard tissues [3] and [4]. It is well understood that minor and trace elements are associated with the properties of biological apatites and they play a major role in the biochemistry of bone, enamel and dentin [9] and [10]. Silicon is one of the trace elements known to be essential in biological processes, while its incorporation in the HA lattice is considered to be a potential method for improving the bioactivity of (HA). As long ago as the 1970, Carlisle [11] and [12] pointed out the importance of Si(IV) in metabolic processes associated with bone formation and calcification, and Gibson et al [13] reported that silicon-containing hydroxyapatite (Si-HA) enhanced and stimulated osteoblast-like cell activity in vitro. Porter and al. [14] mentioned a higher in vivo dissolution rate of SiHAp than that of pure HAp, while Hing and al. [15] reported that Si-HA with 0.8 wt.% Si gave an optimal response in vivo to stimulate both bone-forming and bone-resorbing cells
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