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Biomimetic Transformations of Calcium Phosphates - Thermodynamic and Kinetic Studies

IGIC-BAS. Biomimetic Transformations of Calcium Phosphates - Thermodynamic and Kinetic Studies. D . Rabadjieva 1 , S . Tepavitcharova 1 , R . Gergulova 1 , R . Titorenkova 2 , E . Dyulgerova 3 , O. Petrov 2 , Chr. Balarew 1 didiarab@svr.igic.bas.bg.

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Biomimetic Transformations of Calcium Phosphates - Thermodynamic and Kinetic Studies

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  1. IGIC-BAS Biomimetic Transformations of Calcium Phosphates - Thermodynamic and Kinetic Studies D. Rabadjieva1, S. Tepavitcharova1, R. Gergulova1, R. Titorenkova2, E. Dyulgerova3, O. Petrov2, Chr. Balarew1 didiarab@svr.igic.bas.bg 1Institute of General and Inorganic Chemistry, BAS 2Instituteof Mineralogy and Crystallography, BAS 3Dental Medicine Faculty, University of Medicine September 18-21, 2010, Nessebar, Bulgaria

  2. INTRODUCTION CALCIUM PHOSPHATES ortho- (PO43–) meta- (PO3– ) pyro- (P2O74–) poly-((PO3)nn–) September 18-21, 2010, Nessebar, Bulgaria

  3. INTRODUCTION CALCIUM ORTHOPHOSPHATES (COPh) COPh precipitated from solutions Ca/P pH-lgKso MCPM Ca(H2PO4)2.H2O 0.50 - 2 1.14 DCPD Ca(HPO4)2.2H2O 1.02 - 66.59 OCPt Ca8(PO4)4(HPO4)2.5H2O 1.33 5.5 - 7 96.6 ACP Ca9(PO4)6.nH2O1.5 5 - 12 25.5 PCA Ca10-xx(PO4)6-x (HPO4)x.((OH)2-xx) 1.33 -1.67 6.5 - 9.5 HA Ca10(PO4)6(OH)21.67 9.5 - 12116.8

  4. INTRODUCTION CALCIUM ORTHOPHOSPHATES (COPh) COPh High-Temperature Forms Ca/P Stability MCPA Ca(H2PO4)20.5< 100oC DCPA Ca(HPO4)21.0< 100oC TCP -Ca3(PO4)21.5 < 800oC -Ca3(PO4)21.5 < 1200oC HA Ca10(PO4)6(OH)21.67 till ~1000oC ТТCP Ca4(PO4)2О2.0 < 1500oC

  5. INTRODUCTION CALCIUM ORTHOPHOSPHATES (COPh) Importance forthe Biological system They are the main inorganic component of all body hard tissues Biological apatite • Nano-sized • Poorly crystallized • Non-stoichiometric hydroxyapatite • Including Na, K, Mg, Cl, F and CO3 September 18-21, 2010, Nessebar, Bulgaria

  6. INTRODUCTION MATERIALS FOR BONE REGENERATION CERAMICS CEMENTS Good biocompatibility;Low toxicity HA  / -TCP HA + -TCP DCPD PCA Porous, Nano-sized, Adequate biodegradable rates, High strength and elasticity September 18-21, 2010, Nessebar, Bulgaria

  7. INTRODUCTION BIOMIMETIC APPROACH BIOMIMETICS (bionics, biognosis and/or biomimicry) application of the methods and systems found in natureto study, design andconstruct new engineering systems, materialsand modern technologies. September 18-21, 2010, Nessebar, Bulgaria

  8. INTRODUCTION BIOMIMETIC APPROACH Biological mineralization (biomineralization) process of in vivo formation of inorganic minerals BLOOD PLASMA It acts as a reservoir for Ca2+ and PO43- as well as a maturation medium. September 18-21, 2010, Nessebar, Bulgaria

  9. INTRODUCTION BIOMIMETIC SOLUTIONS Blood HBSS EBSS SBFc SBFr SBFi Plasma Na+ 142.0 142.1 143.5 142.0 142.0 142.0 K+ 5.0 5.3 5.4 5.0 5.0 5.0 Ca2+2.5 1.26 1.8 2.5 2.5 1.6 Mg2+ 1.5 0.9 0.8 1.5 1.5 1.0 Cl- 103.0 146.8 123.5 147.8 125.0 103.0 HCO32- 27.0 4.2 26.2 4.2 27.0 27.0 HPO42- 1.0 0.78 1.0 1.0 1.0 1.0 SO42- 0.5 0.41 0.8 0.5 0.5 1.5 Ca/P 2.5 1.62 1.8 2.5 2.5 1.6 Buffer TRIS TRIS TRIS pH 7.4 6.7–6.9 7.2-7.6 7.2-7.4 7.4 7.4

  10. AIMS To study the biomimetic synthesis and transformations of X-ray ACP and DCPD in conventional, revised and modified with Glycine SBF in order to elucidate some elementary processes of hard tissue mineralization and of the influence of micro-environmental surroundings on synthesis and transformation processes. September 18-21, 2010, Nessebar, Bulgaria

  11. EXPERIMENTS BIOMIMETIC SYNTHESIS EXPERIMENTAL CONDITIONS ACP DCPD Ca/P = 1.67 Ca/P = 1 pH 11.5 (KOH) pH 6 Room temperature; Fast mixing Filtering Washing (water : acetone = 1:1) Freezing -18oC Drying (37oC) SBFc-Cam SBFc-Pm K2HPO4 CaCl2 K2HPO4 September 18-21, 2010, Nessebar, Bulgaria

  12. EXPERIMENTS BIOMIMETIC TRANSFORMATION • Conditions • SBFc, SBFr, SBFg (~SBFc + Glycine) • 37oC, pH 7.3; • Static regime; Solid/liquid ratio 4 g/l ; • Duration – 1, 2, 4, 6, 24 h, 3, 10 days, 1 and 6 months; • SBF solution changes - after 3-rd day SBF September 18-21, 2010, Nessebar, Bulgaria

  13. EXPERIMENTS THERMODYNAMIC CALCULATIONS PHREEQCI computer program INPUT pH, toC, Initial solution concentrations DATABASE for K, H of the reaction for complex formation and precipitation CALCULATION DAVIES equations, OUTPUT Precipitation phase Solutions September 18-21, 2010, Nessebar, Bulgaria

  14. RESULTS ACP precipitation Compositions of the initial precipitated solid phase Mg Na KCl Ca/PO4 mmol/g 0.13 0.20 0.450.03 1.51 Enamel, Dentin and Bone 0.02 - 0.29 0.22 - 0.392.10-4 - 0.020.03 – 0.11.6–1.7 XRD powder data and IR spectra September 18-21, 2010, Nessebar, Bulgaria

  15. RESULTS ACP precipitation Formation of Posner clusters Ca9(PO4)6 covered with hydrated shell CO32- ions from the solution compete with and partially replace the PO43- ions RESULT  Ca vacancies Ca vacancies could be occupied by free Na+, K+ and Mg2+ ionsfrom the solution RESULT CawMgxNayKz(PO4)v(CO3)6v September 18-21, 2010, Nessebar, Bulgaria

  16. RESULTS ACP precipitation Thermodynamic calculated saturated indices (SI) SI = lg(IAP/K) where IAP is an ion activity product, and K is a solubility product. September 18-21, 2010, Nessebar, Bulgaria

  17. RESULTS ACP precipitation • Ionic substitution • Co-precipitation • Incorporation of maternal solution • LEAD TO • precipitation of calcium deficient, X-ray amorphous phosphate • mineral composition similar to those in the hard tissues (enamel, dentin, and bone mineral) September 18-21, 2010, Nessebar, Bulgaria

  18. RESULTS ACP transformation KINETIC STUDIES PO43- Ca2+ Mg2+ Kinetic profile of PO43-, Ca2+ and Mg2+ contents in liquid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  19. RESULTS ACP transformation KINETIC STUDIES Ca/PO4 Mg/Ca Kinetic profile of Ca/PO4 and Mg/Ca ratios in solid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  20. RESULTS ACP transformation XRD STUDIES XRD powder data of solid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  21. RESULTS ACP transformation IR STUDIES IR spectra of solid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  22. RESULTS ACP transformation IR STUDIES Changes in the carbonate content of the samples treated in SBFc and SBFr September 18-21, 2010, Nessebar, Bulgaria

  23. RESULTS ACP transformation THERMODYNAMIC STUDIES Calculated saturated indices (SI) M(m) - - - 0 0 M(eq) - - - - - - - 0 Pr Mg(OH)2+ Mg3(PO4)2.8H2O + MgCO3.Mg(OH)2.3H2O + CaCO3+ Ca3(PO4)2(am) + Ca8H2(PO4)6.5H2O + Ca9Mg(HPO4)(PO4)6+ Ca10(PO4)6(OH)2+ September 18-21, 2010, Nessebar, Bulgaria

  24. RESULTS DCPD precipitation Chemical composition of the precipitate Ca/PO4 Mg Na K Cl mmol/g 0.95 0.001 0.025 0.001 0.003 XRD and IR spectra of the precipitate September 18-21, 2010, Nessebar, Bulgaria

  25. RESULTS DCPD precipitation Thermodynamic simulations of the precipitation process in the studied system (pH 4 - 6) September 18-21, 2010, Nessebar, Bulgaria

  26. RESULTS DCPD transformation KINETIC STUDIES PO43- Ca2+ Mg2+ Kinetic profile of PO43-, Ca2+ and Mg2+ contents in liquid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  27. RESULTS DCPD transformation KINETIC STUDIES Kinetic profile of Ca/PO4 ratios in solid phases after different maturation times September 18-21, 2010, Nessebar, Bulgaria

  28. RESULTS DCPD transformation XRD STUDIES XRD powder data of matured solid phases in different SBFs ___ DCPD; ____ DCPD+OCP; _____ OCP; _____ PCA September 18-21, 2010, Nessebar, Bulgaria

  29. RESULTS DCPD transformation IR studies IR spectra of matured solid phases in different SBFs September 18-21, 2010, Nessebar, Bulgaria

  30. RESULTS DCPD transformation THERMODYNAMIC STUDIES Calculated (____) and experimental (■ ;; ▲) pH and Ca values of liquid phase September 18-21, 2010, Nessebar, Bulgaria

  31. CONCLUSSIONS Kinetic reasons determine the biomimetic precipitation of XRD amorphous calcium phosphate (ACP) and dicalcium phosphate dihydrate (DCPD) that are a less thermodynamic stable phases in comparison with calcium hydroxyapatite; The precipitated salts always contain impurities due to the parallel co-precipitation, ion substitution and maternal liquor incorporation. Their content depends on the nature and crystallinity of the precipitants; Both ACP and DCPD transforminto poorly crystalline apatite in the studied SBFs microenvironments. An intermediate phase of octacalcium phosphate (OCP) was registered for DCPD only. September 18-21, 2010, Nessebar, Bulgaria

  32. CONCLUSSIONS The SBF composition influences the polymorphous phase transformation and its rate - HCO3- ions accelerate the transformation rates both of ACP and DCPD while the Glycine increases the transformation rate of ACP only. The phase transformations of ACP and DCPD leaded to changes in the chemical compositions of solid and liquid phases. Thermodynamic simulations reveal that these phenomena could be explained by the processes of dissolution/crystallization/co-crystallization/ion-exchange. September 18-21, 2010, Nessebar, Bulgaria

  33. Thank you for your attention September 18-21, 2010, Nessebar, Bulgaria

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