Biomimetic dendrimers for mineralization: rare fibrous amorphous calcium carbonate (ACC) and branch-and-bud ACC-vaterite polymorphs

Inorganic mineralization plays a vital role in numerous biological, chemical, and pharmaceutical processes, ranging from hard-organ development through the so-called biomineralization to the synthesis of functional hybrid materials. Inspired by living organisms, a great effort has been devoted to directing the mineralization pathways toward obtaining rare polymorphs. We have synthesized a family of dendrimers based on tetraethylene glycol (TEG) backbone, symmetrically decorated with phosphonate groups on their surfaces, to engineer the interactions among precipitating ions and stabilize early-stage polymorphs under ambient conditions. In a model system, the mineralization of calcium carbonate was templated with a ppm level of TEG-based dendrimers, resulting in the first experimental observation of unique branch-and-bud CaCO₃ structures, wherein amorphous calcium carbonate (ACC), the branch, was decorated with vaterite (buds). Favorable directional growth of ACC, stabilization of vaterite, and secondary nucleation were identified as key mineralization phenomena. Dendrimer generation, regulating molecular flexibility and functional group density, strongly affected the biomimetic mineralization time scale. The outcome of this research may have direct applications in designing hybrid inorganic-organic fibers, ACC and vaterite production, and scale inhibition in water-based industries.