Articulo De Ceramicos

Materials Letters 59 (2005) 3841 – 3846 www.elsevier.com/locate/matlet

Structural characterization of silicon-substituted hydroxyapatite synthesized by a hydrothermal method
Xiao Lian Tang, Xiu Feng Xiao, Rong Fang Liu *
College of Chemistry and Materials Science, Fujian Normal University, Fujian, Fuzhou 350007, China Received 25 March 2005; accepted 28 June 2005 Available online 27 July2005

Abstract Silicon-substituted hydroxyapatite (Si-HA) was prepared successfully by hydrothermal method. The crystalline phase, microstructure, chemical composition, morphology and thermal stability of Si-HA were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The resultsshow that the substitution of the silicate groups for the phosphate groups causes some OH- loss to maintain the charge balance and changes the lattice parameters of HA. Furthermore, the substitution of the silicate groups restrains the growth of Si-HA crystal. DSC analysis shows that the small amount of silicon incorporates into HA lattice does not influence the thermal stability of HA. D 2005Elsevier B.V. All rights reserved.
Keywords: Silicon; Hydroxyapatite; Hydrothermal; Thermal properties; Microstructure

1. Introduction Hydroxyapatite [Ca10(PO4)6(OH)2, HA] is used as a bioceramic due to its bioactivity and osteoconductive properties in vivo [1]. The advantage of using HA as a bioceramic or biomaterial compared to other bioceramics, such as Bioglass or A-W glass-ceramic, is itschemical similarity to the inorganic component of bone and tooth. Apatites are currently used for bioactive coating for metallic prostheses, inorganic filler in ceramic-polymer composite biomaterials, or as a material to fill small bone defects [2]. However, the disadvantage of using HA implant in comparison with bioactive glasses and ceramics is that its reactivity with existing bone is low, andthe rate at which bone apposes and integrates with HA is relatively low. These properties could have implications for the time required for patient rehabilitation [3]. One way to enhance the bioactive behavior of hydroxyapatite is to obtain substituted apatite, which resemble the
* Corresponding author. Tel.: +86 591 83465190; fax: +86 591 87609532. E-mail address: rfliu@vip.sina.com (R.F. Liu).0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.06.060

chemical composition and structure of the mineral phase in bones [4,5]. These ionic substitution can affect the surface structure and charge of hydroxyapatite, which would have an influence on the material in biological environments. In this sense, an interesting way to improve thebioactivity of hydroxyapatite is the addition of silicon to the apatite structure, taking into account the influence of this element on the bioactivity of bioactive glasses and glass-ceramics [2].The studies carried out by Carlisle [6] indicated the importance of the silicon on bone formation and calcification. Moreover, it has been observed that the addition of Si during the HA synthesis leads to animprovement of the bioactive behavior [7 –12]. This means that the implant is able to join chemically to the bone through a strong ‘‘bioactive bond’’. In this way, the osteointegration and the good performance of the implant are ensured. Several authors have worked on this subject, assuming that Si or 4À 3À SiO4 , replaces P or PO4 , respectively, at the 6 h positions, with the subsequent loss ofcharge equilibrium [13]. Several methods of the synthesis of silicon-substituted hydroxyapatite have been described. Ruys [14] suggested the use of a sol –gel procedure, however, these materials,

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X.L. Tang et al. / Materials Letters 59 (2005) 3841 – 3846

besides the hydroxyapatite phase, include other crystalline phases depending on the substitution degree of silicon. Boyer et al. [15]...