The effects of different types of additives on growth of biomineral phases investigated by in situ atomic force microscopy

•Effects of Mg2+ and Asp6 on step growth on (−1 0 1) face of COM crystal were compared.•Differences in the effects of Mg2+ and Asp6 were explained based on a De Yoreo model.•Effects of BSA and PSPMA30-PDPA47 micelle on the calcite {1 0 4} growth were compared.•Factors in determining macromolecule incorporation into minerals were suggested. Interactions between different types of additives with specific crystal surfaces of mineral phases found in biominerals were investigated at nanometer and micrometer scales by in situ atomic force microscopy (AFM). Firstly, the inhibitory effect of magnesium ion (Mg2+) and that of a peptide molecule, L-aspartic acid 6mer (L-Asp6) on the growth of a fast growing [−1 0 −1] step on the (−1 0 1) face of calcium oxalate monohydrate (COM) crystal are quantitatively compared by the step speed data. Differences in the inhibitory effect are explained based on a De Yoreo model of step kinetics in detail. The step speed data show that Mg2+ had a little inhibitory effect on the growth of the [−1 0 −1] step, approaching a limiting value of about 15% reduction in the step speed, whereas L-Asp6 was substantially more effective in inhibiting the step growth with an ability to stop the growth completely. Secondly, the effects of a protein molecule, bovine serum albumin (BSA) and a pseudo protein-like organic particle PSPMA30-PDPA47 micelle on the growth of calcite on its {1 0 4} faces are compared. Both BSA and PSPMA30-PDPA47 micelle temporarily pinned the passing steps without or negligibly inhibiting the step growth overall. The BSA molecule remained at the crystal surface without incorporation into the crystal because the steps passed through it, pushing it up and out. However, in contrast to the BSA, the micelle was incorporated into the crystal by the passing steps. These results together with other relevant studies suggest that the decisive factor in determining for macromolecules to be incorporated into growing minerals or to remain intact on the mineral surface with no incorporation is the magnitude of binding strength of the macromolecules to the growing step against the step’s propagation force.