Hierarchical Calcium Carbonate Structures Using Microgel As Template: Preparation And Mineralization Mechanism

Poly(acrylamide-co-sodium acrylate)(P(AM-co-SA))microgel contains a large amount offunctional groups like-NH2and-COO-, whose chemical structures and network structures arevery similar to the natural protein. Therefore it is significant to use it as organic template for thestudy of CaCO3biomineralization and biomimetic synthesis. In this paper, P(AM-co-SA)microgel was synthesized through a reverse microemulsion radical polymerization method, inwhich mineralization reaction was occurred. A core-shell structure of CaCO3nanoparticles wasprepared and the mineralization process was studied. Furthermore, a kind of magnetic CaCO3microparticles was prepared based on this system and the release behavior of ibuprofen wasstudied. The results were as follows:1. Poly(acrylamide-co-sodium acrylate) microgel with50%sodium acrylate wassynthesized in reverse microemulsion system, in which mineralization reaction was carried outwith the inorganic reactant diffusing into the microgel, and a nuclear calcite-vaterite shellstructured calcium carbonate nanoparticle was prepared. The research suggests that there is acompetitive relationship between the growth of calcite and vaterite in the process ofmineralization process, which was contributed to the formation of core-shell structures. Furtherstudy confirmed that shuttle-like calcite core was composed of (001)-oriented calcitenanoplatelets, while the vaterite shell was composed of vaterite nanoparticles. Additionally, themineralization process of calcium carbonate was effected by adding some small molecular, likeMg2+and amino acids, which tend to effect the mineralization process and form new morphologyof calcium carbonate. This effect was also studied in this article.2. The formation mechanism of calcium carbonate microspheres was studied. The–COO-groups can promoted the formation of calcite core, due to the–COO-groups can stabilize the(001) plane of calcite crystals through stereochemically matched electrostatic interactions. While–NH2groups can stabilize the (001) plane of vaterite crystals through stereochemically matchedhydrogen bonding interactions. Therefore, the polymorphic characters and core-shell structuresof CaCO3were also able to control by changing the ratio of sodium acrylate/acrylamide in microgels. The studies confirmed that the growth of calcite core was promoted by increasing theproportion of-COO-in microgel, while the growth of vaterite shell was promoted by increasingthe proportion of-NH2in microgel. Additionally, the mineralization process of calciumcarbonate was effected by adding some small molecular, like Mg2+and amino acids, which tendto form new morphology of calcium carbonate.3. Two kinds of magnetic calcium carbonate microspheres, Fe3O4@CaCO3andFe3O4-doped CaCO3microsphere were prepared and their drug release behaviors were studied.Drug release experiments show both the two magnetic calcium carbonate microspheres havesustained release properties, and Fe3O4-doped calcium carbonate microspheres showed a moredurable and stable drug release behavior. These magnetic calcium carbonate microspheres isexpected to get a broad field in the magnetic targeting drug delivery and will also show profoundsignificance for the treatment of cancer and other diseases.