Poster P36 Calcium ortophosphates possess good biocompatibility, little toxicity and an adequate biodegradable rate when they are used as bone substitutes in a view of ceramics or cements. Dicalcium phosphate dihydrate (DCPD, CaHPO4.2H2O) as calcium orthophosphates, attracts the interest due to its relevance to biological systems. DCPD is detected in pathologic mineralization and it is considered to be an intermediate phase in the processes of bone and teeth de- and re- mineralization. Thus, investigations on the biomimetic synthesis and phase transformation of DCPD are of great importance for elucidation of some of the elementary processes of hard tissue mineralization. Introduction Experiments and Results Conclusions  DCPD with minor impurities of Mg, Na, K and Cl precipitates at these experimental conditions;  DCPD dissolution during the first 1-2 hours causes pH increasing in all maturation solutions. The effect is greater at SBFc and SBFr than in SBFcg and SBFcu since Glycine and Urea operate as additional buffer system together with HPO 4 2- /Н 2 PO 4 - and HCO 3 - /CO 3 2- ;  Тhe solubility of DCPD increases in SBFcg and SBFcu, due to the tendency of Glycine and Urea to form calcium complexes [Ca 2+ (Gly) n ] 2-n or [Ca 2+ U n ] 2-n ;  Тhe phase transformation of DCPD into OCP is completed after 240h in SBFc, SBFcg and SBFcu, six months later formation of carbonated apatite phase takes place  In SBFr the phase transformation carries out faster and phase of carbonated apatite was registered still after 240th hours Acknowledgments This work is financially supported by the Bulgarian Ministry of Education, Youth and Science under Projects DTK 02-70/2009 and CVP BIOMIMETIC SYNTHESIS AND TRANSFORMATIONS OF DICALCIUM PHOSPHATE DIHYDRATE D. Rabadjieva 1, R. Gergulova 1, R. Titorenkova 2, S. Tepavitcharova 1, E. Dyulgerova 3, O. Petrov 2, Chr. Balarew 1 1 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,Acad. G. Bontchev Str., Bl.11, 1113 Sofia, Bulgaria, 2 Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bontchev Str., Bl.107, 1113 Sofia, Bulgaria 3 Dental Medicine Faculty, University of Medicine, 1 G. Sofiiski Str., 1431 Sofia, Bulgaria Aims To study the biomimetic transformations of DCPD by applying of chemical, thermodynamics, kinetics, and spectral (XRD and IR) analysis. DCPD biomimetic synthesis Initial solutions - SBFc-Pm and SBFc-Cam Composition SBFc-Pm SBFc-Cam mmol/l (CaCl2 solution) (K2HPO4 solution) Na K Mg Ca Cl SO HCO HPO Precipitation method (fast mixing, pH 5.5, room temperature, washing with water and acetone (1:1), drying at 37 o C SBF); Chemical composition of the precipitate XRD and IR analysis of the precipitate Thermodynamic simulations of the precipitation process in the studied system (pH ) SBF maturation Biomimetic conditions (37 o C, pH 7.3, SBFc, SBFr, SBFcg, SBFcu) Static regime, Solid/liquid ratio 4 g/l Duration – 72h, 240h, 720h, 6 monts Change the SBF solution every day after 72nd hour. Kinetics studies XRD studies IR studies Kinetics profile of Mg2+, Ca2+ and PO43- and pH in liquid (a) and solid (b) phases during the process XRD powder data of solid phases obtained at the maturation process in different SBFs ___ DCPD; ____ DCPD+OCP; _____ OCP; _____ carbonated apatite FT IR spectra of solid phases obtained at the maturation process in different SBFs Thermodynamic studies of the dissolution process and phase transformation of DCPD and OCP Calculated (____) and experimental (■ ;  ; ▲) pH and Ca values of liquid phase