| Hydrogels of calcium alginate are the physically cross-linked networks containing a large fraction of water, which could be used as the precursors for the biomimetic mineralization of calcium carbonate (CaCO3) and calcium oxalate (CaC2O4) crystals. Also, these are the main subjects of the thesis.CaCO3:The well-defined geometry, the permeability, and the ion-exchange property of calcium alginate pre-gels favored the facile fabrication of calcite superstructures through the slow inpouring of ammonia and carbon dioxide gases. This strategic approach indicated to a great extent the biologically controlled mineralization mechanism, dealing with (1) the pre-adsorption of calcium ions by the functional groups of biomolecules, (2) the confined crystallization within the three-dimensional networks, and (3) the proper arrangement of nanosized calcites by association with the organic architectures. Surprisingly, even the apparently 'single-crystalline' CaCO3 was proven to comprise tiny calcite rhombohedrons, furthermore these building blocks co-aligned each other with respect to the polymers' conjugated backbones. Therefore, these suggest a novel pathway of multivalent metal pre-gelation phases for the biomimetic fabrication of functional materials.CaC2O4:Calcium oxalate crystals have three hydrate forms:calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD), and calcium oxalate trihydrate (COT), among which COM is the principal inorganic component of urinary deposites and the other two can be easily excreted through urethra. In the in vitro experiments, calcium oxalate crystals were prepared from the mixture of calcium chloride (CaCl2) and ammonium oxalate ((NH4)2C2O4) in different reaction systems at 30℃Only the sheet-like aggregates of COM were precipitated from aqueous systems at various pH values and at a fixed Ca2+concentration of 0.0172 mol/L, so did the reaction systems of the buffer solutions of potassium hydrogen phthalate (pH=4.00). Surprisingly, when Ca2+(0.0172 mol/L) and different amount of C2O42- were added into the buffer solutions of sodium tetraborate (pH=9.18), both COM and COD crystals were obtained at a relatively low concentration of C2O42-. The content of COD decreased with the increase of C2O42- concentration until it disappeared at a relatively high C2O42- concentration.When calcium alginate hydrogels were used as calcium sources, its reaction with (NH4)2C2O4 resulted in spherical aggerates of calcium oxalate crystals. Crystallographic analyses proved that COM and COD coexisted at a relatively low concentration of Ca2+ions. For example, when Ca2+concentration was fixed at a value of 0.0172 mol/L, the 1:1 molar ratio of Ca2+/C2O42-resulted in the major COD (64.0%) and minor COM (36.0%). The content of COD decreased with the increase of C2O42-, and the unique crystals of COM were obtained at a relatively high concentration of C2O42-ions.In conclusion, the above results indicated:(1) the supersaturation at a relatively high concentration of Ca2+or C2O42-ions promoted the nucleation and crystallization of COM; (2) sodium tetraborate buffer reaction systems contributed to the formation of COD crystals at a relatively low concentration of C2O42- ions; (3) calcium alginate hydrogels exerted a great influence on the crystallization of COD and played an important role in the template formation of CaC2O4 crystalline superstructures. Interestingly, the formation of COD suggests a biomimetic pathway for the therapy of urinary stones. |
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