Formation of CaCO₃ fibres directed by polypeptide vesicles

Mineralization behaviour of CaCO₃ in the presence of polypeptide vesicles self-assembled from poly(l-glutamic acid)-block-poly(propylene oxide)-block-poly(l-glutamic acid) (PLGA-b-PPO-b-PLGA) triblock copolymers was studied. Under the mediation of PLGA-b-PPO-b-PLGA vesicles, CaCO₃ fibre clusters were obtained. The structure of fibres could be regulated by the mineralization temperature, copolymer composition, copolymer concentration, and Ca²⁺ concentration. The investigation of the fibre growth process suggested a solution-precursor-solid mechanism via transient amorphous precursors. Since the polypeptide vesicles could serve as both the modifier and template for the formation of amorphous precursors, the properties of amorphous precursors were affected by the vesicular structure. The variation in the fibre structure was ascribed to the different aggregation and transformation behaviours of amorphous particles. These findings can provide useful information for the design of novel inorganic materials with fibrous structures and enrich our existing knowledge of the crystallization process from the amorphous phase.