Biomimetic Synthesis Of Vaterite Calcium Carbonate And Application On Drug Carrier

In this paper, mesoporous spherical vaterite was synthesized with aspartic acid by the Ca(OH)2-CO2 reaction. We studied the formation mechanism of vaterite with aspartic acid, and proposed the intermediate calcium aspartate.We studied different factors on the polymorph and morphology of calcium carbonate by Ca(OH)2 suspension. Vaterite with the high mole fraction was prepared successfully, and we discussed the physicochemical change during the crystallization and the heterogeneous nucleation. Furtherly, the excellent mesopore and adsorptivity of vaterite microspheres allowed for an effective drug loading and controllable drug release. The main experimental content and results are as follows:1. The intermediate calcium aspartate of the crystallization of vaterite was proposed in the clear limewater and the complexation constant of calcium aspartate was tested. The influence of reaction temperature and Asp concentration on the process of crystallization was explained successfully. We also found that the calcite with regular cube was formed by ionic Ca2+ and CO32-, and the calcite with spheroidal lamellate profile stemed from the dissolution and recrystallization of vaterite.2. The process parameters influenced on the polymoph and morphology of calcium carbonate. The results showed that the CO2 flow rate and Ca(OH)2 concentration had no impact on calcium carbonate and the mole fraction of vaterite could reach about 95%. The reaction temperature had a little impact on calcium carbonate, and the mole fraction of vatere was 96% at low temperature period (20℃), the mole fraction of vaterite decreased to 87% when the temperature riseed. Asp concentration had remarkable impact on calcium carbonate, and the mole fraction of vaterite decreased with increasing Asp concentration and the calcium carbonate changed its shape from sphere to aciculiform.3. The change of pH, conductivity, concentration of OH" and total calcium (ionic calcium Ca2+ and chelate calcium CaY2) in the Ca(OH)2 suspension with aspartic acid. We found the abrupt change in the suspension and proposed the process of heterogeneous nucleation during the precipitation.4. We studied the specific surface area and mesopore structure of vaterite with different mole fraction, and the higher the mole fraction of vaterite, the lager specific surface area and the smaller mesopore is. Vaterite microsphere was used as drug carrier of salicylic acid, and the study on drug loading and controllable drug release in the PBS buffer solution showed that calcium carbonate had prominent drug loading with the increase of mole fraction of vaterite.