Synthesis And Structure Characterization Of Modified Hydroxyapatite

Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HAP) is an excellent kind of synthesized biomaterials with outstanding bioactivity, which has been widely applied to the bone substitutes and bone-defect filling related to the provision of supporting scaffolds for osteoconduction. However, usage of synthetic HAP is limited due to high brittleness and poor plasticity, some difficult for implant shape modification in place during surgical operation.The objectives of the present study were to synthesize and characterize Ca-deficirnt hydroxyapatiter(CDHA) and Zn-doped hydroxyapatite(ZnHA) which more similar with human bone tissue in chemical composition and structure.Rietveld structure and FTIR 2nd derivates deconvolution were used to characterize the crystal structure and molecular structure.The calcium-deficient apatite(CDHA) powders were synthesized by means of a wet-chemical method. Based on HAP crystal model with space group P6₃/m with a=0.9432nm and b=0.6881nm, Rietveld structure refinement was performed on the X-ray diffraction(XRD) experimental data of CDHA powders and Fourier transform infrared spectroscopy was used to characterize structure of CDHA. With the decrease of Ca/P ratio, the crystallite size and crystallinity decreased, but the acid phosphate content and amount of vacancies in hydroxyapatite hexagonal structure increased. The disorder of CDHA structure increase indicated calcium-deficiency and HPO₄ replacement resulted in disorder of crystal in apatite structure. The more calcium is deficient, the more disorder or imperfect in CDHA structure.Then CDHA powders were sintered at 1100℃for 2 and 4 hours to prove that CDHA was the precursor of bi-phase calcium phosphates(BCP) and able to transform to BCP. For CDHA with certain Ca/P molar ratio, BCP with different hydroxyapatite/tricalcium phosphate(HAP/TCP) ratio could be fabricated by adjusting the length of sintering periods. After 4 hours sintering, the transformation of CDHA was completed and CDHA were transformed to HAP,β-TCP, or BCP with desired phase compositions. From the chemical analysis on CDHA and the XRD quantitative analysis on BCP, this method of synthesis was shown to produce CDHA with same apatite structure and HAP in BCP ceramics fabricated by incomplete sintering CDHA is also calcium-deficient apatite, which is more similar with bone than stoichiometric hydroxyaptite.On the other hand, Zn-doped hydroxyapatite(ZnHA) powders with similar apatite structure were synthesized also using a wet-chemical method. The effect of different content of doped Zinc on HAP structure was studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray energy dispersive spectrum (EDS). The (Ca+Zn)/P molar ratio, content of zinc of Zn-doped HAP were also tested.In addision, Rietveld structure refinement was performed on the X-ray diffraction (XRD) experimental data of ZnHA powders. With the increase of doped Zinc, the crystallite size and crystallinity decreased, but the microstrain increased.During sintering temperature up to 1100℃, the ZnHA keep hexagonal structure of apatite without obvious impure phase, such as, ZnO, CaO, Ca₃(PO₄)₂. The results showed Zn²⁺ replaced the Ca²⁺ in the hydroxyapatite lattice to form ZnHA, and keep ZnHA crystalline structure with hexagonal structure apatite.