Silk fibroin-mediated biomineralization of calcium carbonate at the air/water interface

Abstract

The synthesis of calcium carbonate (CaCO₃) with different morphologies and polymorphs at the air/water interface has been reported in previous studies while the influence of the structure of macromolecular additives on this type of mineralization is rarely investigated. Regenerated silk fibroin (RSF) from the Bombyx mori silkworm silk is analogous to the main protein contained in naturally formed nacre, which can form complex structures at the air/water interface due to the multi-block amphipathy. This study demonstrates how a range of CaCO₃ structures with different morphologies and polymorphs was obtained at the air/water interface mediated by RSF. The precursor-stabilizing ability of RSF allows the crystals to grow directly from amorphous calcium carbonate (ACC), which was observed by time-dependent experiments. The structures of RSF that exist at the interface determine the final morphologies and polymorphs of the crystals, which can be influenced by the concentrations of [RSF] and [Ca²⁺] and the molecular weight of RSF. A thermodynamically metastable aragonite phase may be mediated by the β-sheets of RSF formed at low concentrations, while stable calcite can be generated by the RSF amorphous structure at high concentrations. The synergy between RSF and CaCO₃ at the interface can provide a way to understand the function of organic materials involved in the biomineralization process and can be applied to manipulate the structures of synthetic hybrid materials.