Silk fibroin hydrogels coupled with the n16N-β-chitin complex: An in vitro organic matrix for controlling calcium carbonate mineralization

Previous results have shown that the nacre specific peptide, n16N, from the Japanese pearl oyster Pinctada fucata has a binding affinity for β-chitin. As a result, the n16N-chitin assembly is able to selectivity nucleate aragonite. Here, we have added silk fibroin hydrogels to the in vitro assay to more fully represent the in vivo matrix. Crystallization, with a silk fibroin hydrogel and n16N on β-chitin, results in metastable vaterite and amorphous calcium carbonate, which form as flat deposits with hemispherical centers. Acidic peptide controls (p-Asp/p-Glu) were also tested in the silk-chitin assay and result in flat calcite that grows into the β-chitin substrate. Fluorescence imaging of that matrix, made with labeled n16N, shows that n16N binds to β-chitin in the presence of silk gel. These results demonstrate that the addition of a silk hydrogel to the n16N-β-chitin assembly changes the microenvironment for mineralization. This work contributes to our understanding of the roles of individual nacre matrix components (and their assemblies) in controlling crystal growth.