Aragonite Nanorod Arrays through Molecular Controlled Growth on Single-Crystalline Substrate and Polysaccharide Surface

We produced bunched aragonite nanorods through crystal growth controlled by an acidic polysaccharide, alginate, in a supersaturated solution. The highly ordered arrays of c-axis-elongated aragonite nanorods ∼100 nm in diameter were grown on the (001) surface of a single-crystalline aragonite substrate with specific adsorption of the soluble polysaccharide. Freestanding films consisting of ordered aragonite nanorods were obtained by using an insoluble polysaccharide, anhydrous chitosan, as a template for nucleation of the metastable phase. The orientation of the ordered rods in the films was improved by repetition of the crystal growth. Parallel control of the polymorphism, orientation, and morphology by molecular controlled crystal growth provides biomimetic hierarchical architectures of the metastable calcium carbonate crystals.