Cryst. Res. Technol. 45, No. 7, 685 – 691 (2010) / DOI 10.1002/crat.201000163 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Thermal transformations of the mineral component of composite biomaterials based on chitosan and apatite S. N. Danilchenko* 1 , O. V. Kalinkevich 1 , V. N. Kuznetsov 1 , A. N. Kalinkevich 1 , T. G. Kalinichenko 1 , I. N. Poddubny 1 , V. V. Starikov 2 , A. M. Sklyar 3 , and L. F. Sukhodub 1 1 Institute for applied physics, Sumy, Ukraine 2 National technical university “Kharkov polytechnic institute”, Kharkov, Ukraine 3 Sumy state pedagogical university, Sumy, Ukraine Received 12 March 2010, revised 31 March 2010, accepted 7 April 2010 Published online 23 April 2010 Key words apatite, chitosan, composite biomaterials, annealing, X-ray diffraction. Composite biomaterials based on chitosan and calcium apatite with different chitosan/apatite ratio were prepared by chemical synthesis of apatite in chitosan solution using one-step co-precipitation method. Initial and annealed samples were characterized by X-ray diffraction, FTIR spectroscopy and scanning electron microscopy coupled to energy-dispersive electron X-ray spectroscopy. The data obtained suggest that the formation of the calcium-phosphate mineral in chitosan solution is substantially modulated by the chemical interaction of the components; apparently, a part of calcium is captured by chitosan and does not participate in the formation of the main mineral phase. The apatite in the composite is calcium-deficient, carbonate- substituted and is composed of dispersed nano-sized crystallites, i.e. has properties that closely resemble those of bone mineral. Varying synthesis, drying and lyophilization conditions, the composite materials can be produced with the desirable chitosan/apatite ratio, both in the dense and porous form. The structural analysis of composite samples after annealing at certain temperatures is examined as an approach to elucidate the mechanism of co-precipitation by one-step method. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction The current interest to the biomaterials based on chitosan and calcium apatite [1-6] is caused by their high biocompatibility, good mechanical characteristics, relatively low price and simplicity of preparation and characterization. Structurally these materials resemble the natural bone tissue, in which the fibrillar protein collagen serves as an elastic matrix, while the nanocrystals of biogenic apatite reinforce the bone strength [7]. In the chitosan-apatite composites the high-molecular chains of natural polysaccharide chitosan function as an elastic matrix, while the synthetic apatite is a reinforcing component. Chitosan is the simplest derivative of chitin produced by its deacetylation. Chitin is an abundant natural polysaccharide, it is the base of the skeletal system of Crustacea, cuticule of insects, cell walls of fungi and some bacteria. Hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) can, with some approximation, be regarded as a crystallochemical analogue of mineral part of animal and human skeletons. It has been used for a long time as a basic component of a wide range of synthetic materials in orthopaedy and dentistry [8]. Recently the interest in chitosan-apatite composite biomaterials has increased significantly, evidenced by the growth of related scientific papers number. Different preparation methods of such materials production have been developed. Most of them involve two major stages: first, the synthesis of the organic polymeric scaffolds of pure or chemically treated and modified chitosan; and second, mineralization of the scaffold either in the simulated body fluid (the biomimetic way) or in saturated matrix solutions [2,5,9]. An inverse approach has also been described – the pre-formation of a porous hydroxyapatite scaffold followed by its impregnation with chitosan [10]. Yamaguchi et al. [1] have described a one-step scheme of chitosan-hydroxyapatite synthesis, in which the composite was co-precipitated by dropping chitosan solution containing phosphoric acid into a calcium hydroxide suspension. Rusu et al. have developed a co-precipitation approach using it to ____________________ * Corresponding author: e-mail: danil50@hotbox.ru