Structural Analysis and Characterization of Cu, Sr-doped Hydroxyapatite Whiskers

Cu and Sr ions doped hydroxyapatite (Ca10(PO4)6(OH)2, HA) whiskers were synthesized by hydrothermal homogeneous precipitation method. The morphology, structure and the phase composites of the products were characterized by XRD, FTIR and SEM. The results showed that Cu or Sr partially substituted for Ca in the HA crystal, resulting in lattice distortion and lower crystallinity with Sr or Cu addition. For Cu-doped HA (Cu-HA) whiskers, the doping limit proportion should be below 8mol%, and for Sr-doped HA whiskers (Sr-HA), it was below 20mol%. Introduction Hydroxyapatite (Ca10(PO4)6(OH)2, HA) is the main inorganic component of vertebrate bones and teeth. Synthetic HA has been gradually accepted and widely used to repair bone and tooth defects due to its similarity with the composition of human hard tissue [1,2]. It was well known that most HA of natural bone is non-stoichiometric because of the presence of minor constituents, such as cations (Na、Mg、Sr、Zn、K) and anions (HPO4、CO3、 Cl). Metal ions in bone tissue have been proven to play an active role in promoting bone mineralization and angiogenesis [3,4]. However, for the synthetic HA, only Ca、P、O and H elements remain in the crystal structure, showing a higher stability than that of natural apatite. Thus, ions doping has been attracted more attention to improve the biological behavior and clinical application of HA materials [5]. It has been showed that the presence of divalent metal ions (Mg、Zn、Sr) in HA crystals not only affected their crystallization behavior, solubility and surface chemical properties, but also exerted a positive influence on the formation of bone mineral and the biological characteristics of HA materials [6-8]. Mg doping has been confirmed to be able to regulate the formation and remodeling of bone tissue; Ren et al, reported that when the molar fraction of Zn in artificial bone was in the range of 5-20%, Zn substitution in the apatite lattice, rather than adsorption on the surfaces, and it had a direct stimulation on the growth of osteogenesis cells, while relatively inhibit the growth of osteoclast [9,10]. Comparing with pure HA, Li et al, found that 5-50 mol% Sr-doped HA had better biocompatibility and biological activity; Kim et al found that ceramics based on HA made in a wet chemical process with addition of Cu(NO3)2·3H2O had good antimicrobial [11,12]. Although the effects of these metal ions doped HA on the structure, solubility and biological performance have been made in the previous studies, few literatures focus on metal ions doped HA whiskers. Therefore, effects of Sr and Cu doping on the structure and morphology of HA whiskers will be made in this study so as to find a reasonable doping moral proportion of Cu and Sr ions in HA crystals. International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 270 2θ(°) Fig.1 XRD patterns of Sr ions doped HA whiskers Materials and Methods Preparation of metal ions doped HA. Metal ions doped HA whiskers were synthesized by a hydrothermal homegeneous precipitation method according to the following reaction equation [13]: (10-x)Ca + xM + 6PO4 + 2H2O Ca(10 -x)M x(PO4)6(OH)2 + 2H (0≤x≤10) (1) M = Sr, Cu Appropriate amounts of aqueous solution containing 0.05 mol/L Ca+ M and 0.03 mol/L PO4 were first prepared by dissolving Ca(NO3)2·4H2O, NH4H2PO4, Sr(NO3)2 or Cu(NO3)2·3H2O in a 250ml volumetric flask under constant stirring with teflon-coated magnetic stirring bar, in which doping proportion of Sr was 5-40mol%, and for Cu was 5-15mol%. 1mol/L C2H5NO was added into the mixed solution and its pH was adjusted to 3.00 by addition of 1mol/L HNO3 and 1:1 NH4OH solutions under constant stirring; after the configured solution was heated at 180°C for 10-12h in a hydrothermal reactor, the precipitates were filtered with a vacuum filter, and washed three times with deionized water, finally dried at 70-80°C for 1-2h in a vacuum oven for use. Materials characterization. Rotation Anode High Power X-ray Diffractormeter (XRD) (D/MAX-RB, Rugaku Corporation, Japan) was used to analyze the phase composition of the precipitates in the range 2θ=10-65° with Cu Kα radiation. The Fourier-transform infrared spectroscopy (FTIR) (FTIR, Nicolet IS10, Thermo Nicolet, USA) was recorded in the range of 4000-400 cm to identify and analyze the functional group of the samples. Microstructural feature of the samples was observed by a Scanning Electron Microscope (SEM) (SEM, JSM-5610LV, JEOL, Japan). Results and discussion Sr doped HA. Fig.1 showed the XRD patterns of Sr-doped HA (Sr-HA) prepared with different moral ratio of Sr/(Ca+ Sr). For Sr doping concentration less than 20 mol%, the diffraction peaks were identified as HA, and the ratio of I(300)/I(211) of the Sr-HA whiskers was lower than that of synthesied HA indicated in the JCPDS PDF 09-432. Because Sr radius is bigger than Ca radius, lattice distortion occurrs when Sr substitutes Ca, leading to a expansion of interplanar crystal spacing (d). According to Bragg equation: λ=2dsinθ, when wavelength (λ) is certain, the diffraction angle (2θ) would be smaller with d spacing. Thus, increasing Sr doping concentration, the diffraction peaks shifted to 10 15 20 25 30 35 40 45 50 55 60 65 pure HA 5% Sr-HA 10% Sr-HA (3 00 ) (1 12 ) (2 11 ) 15% Sr-HA • • • • • • • • 20% Sr-HA • -Ca3(PO4)2 •−Ca10(PO4)6(OH)2 In ten sit y( Co un ts) 40% Sr-HA Fig.2 SEM images of Sr ions doped HA whiskers a,b-5mol%Sr-HA c,d-20mol%Sr-HA