Synthesis of Hydroxyapatite in Polymeric Solutions for Organic-Inorganic Nanocomposites Guiqiu Zheng, Xudong Li*, Xiaomin Wang, Suhong Yu, Zhongwei Gu, Xingdong Zhang Engineering research center in biomaterials, Sichuan University, Chengdu, 610064, P.R. China *corresponding author, e-mail: xli20004@yahoo.com Keywords: hydroxyapatite, poly(vinyl alcohol), poly(acrylic acid), nanocomposites, in situ synthesis Abstract. Synthesis of hydroxyapatite (HA) in organic solutions has received extensive attention in recent years with an attempt to obtain HA of a nanometer level. In this preliminary study, we demonstrated that organic-HA nanocomposites could also be achieved with one step method via in situ mineralization and subsequent crosslinking of organic species. This design was realized through in situ synthesis of hydroxyapatite in poly(vinyl alcohol) and acrylic acid aqueous solution as an organic template. The aforementioned organic-inorganic nanocomposites were analyzed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electrical microscopy, thermal analysis. The comparative structural measurements were also conducted with the synthesized HA with absence of the organic template. The results indicated that the existence of organic species effectively inhibits the growth of calcium phosphate and that relatively pure HA can be obtained in sintered composite products. The present study provides a direct and versatile route for fabrication of nanocomposite biomaterials. Introduction Biomineralization occurs in the organic matrix which forms biominerals with the unique properties [1,2]. Hydroxyapatite (HA) as a kind of bioactive ceramic has been extensively used for bone substitutes. The wet chemistry method is usually adopted to synthesize the initial powder which is then sintered at high temperature to give HA with adequate strengths. Various organic species were reported to introduce to the chemical synthesis of calcium phosphates (CP) [3]. The intervention of organic species effectively reduced the size of synthetic CP particles. The fine CP particles have been shown to facilitate achieving HA ceramics with good mechanical strengths and could also be used for other medical application. Bone is a natural composite composed of nano-sized hydroxyapatite and organic matrix, primarily collagen protein [4]. These two components are elaborately organized so as to meet the requirements of different physiological functions [5]. The combination of organic polymers with HA for bone substitutes gives rise to a composite material with elastic modulus close to natural bone, and meanwhile avoids the fatigue and brittleness of pure ceramic materials. Recently, biomimetic methods have been used to produce organic-HA composites, according to the mechanism of biomineralization [6]. In the present study, the synthesis of CP was conducted in the presence of poly(vinyl alcohol) (PVA) and acrylic acid monomer (AA) aqueous solution. The carboxylic groups of AA will ionize when the pH value of the solution is higher than pKα (about 4.2 for AA), and such Key Engineering Materials Vols. 330-332 (2007) pp. 427-430 online at http://www.scientific.net © (2007) Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 218.6.240.155-19/09/06,04:57:58)