Morphological Evolution of Calcite Grown in Zwitterionic Hydrogels: Charge Effects Enhanced by Gel-Incorporation

The incorporation of charged biomacromolecules is widely found in biomineralization. To investigate the significance of this biological strategy for mineralization control, gelatin-incorporated calcite crystals grown from gelatin hydrogels with different charge concentrations along the gel networks are examined. It is found that the bound charged groups on gelatin networks (amino cations, gelatin-NH₃ ⁺ and carboxylic anions, gelatin-COO^- ) play crucial roles in controlling the single-crystallinity and the crystal morphology. And the charge effects are greatly enhanced by the gel-incorporation because the incorporated gel networks force the bound charged groups on them to attach to crystallization fronts. In contrast, ammonium ions (NH₄ ⁺ ) and acetate ions (Ac^- ) dissolve in the crystallization media do not exhibit the similar charge effects because the balance of attachment/detachment make them more difficult to be incorporated. Employing the revealed charge effects, the calcite crystal composites with different morphologies can be flexibly prepared.