Bioprocessing-Inspired Fabrication of Calcite Prismatic Layers and Growth Mechanisms

Biomimetic mineralization can facilitate the fabrication of materials with intricate hierarchical structures and distinctive functional properties under ambient conditions. However, precise replication of the complex biomineralization process in vitro remains a big challenge. In this study, aimed at mimicking the biomineralization process of calcite prismatic layers of mollusk shells, a peristaltic pump was employed to slowly transport a sodium carbonate solution into a calcium-containing solution in the presence of poly(acrylic acid) (PAA). Through delicate control of the ion transport rate and reaction conditions, a calcite seed layer was first deposited on the chitosan-coated substrate, followed by the fabrication of a continuous, dense, and highly oriented shell-like calcite prismatic structure. The influences of PAA concentration and ion transportation rate on the growth kinetics and morphology of calcite were studied, showing that optimal conditions are required to form the prismatic structure. It was demonstrated that the prismatic structure started from random formation of an individual spherical disk on the seed layer, which grew larger in diameter and fused with adjacent disks. Furthermore, using confocal Raman mapping analysis, the orientation of calcite crystals at different growth stages was revealed. This study provides a novel bioprocessing-inspired strategy to fabricate a uniform calcite prismatic structure and significantly improves our understanding of the growth mechanisms.