Abstract
Biomimetic synthesis of aragonite with various templates in vitro is an important way to understand the biomineralization process and synthesize nacre-like materials. Herein, we used the siphon sheath from the bivalve Lutraria sieboldii as the substrate for the formation of calcium carbonate. We found that the inner layer of the sheath, which is composed of approximately 40% protein and 60% β-chitin, induced the formation of nearly pure aragonite by the transformation of amorphous calcium carbonate (ACC). More surprisingly, unique starfruit-shaped aragonite aggregates were observed on the substrate and were constructed from many adhered, oriented aragonite tablets. We consider that the acid-rich protein from the inner layer of the siphon sheath triggers the formation of ACC, and the swollen β-chitin regulates the transformation of ACC into aragonite by lattice matching and stereochemical recognition. The various surface adhesion energies of the crystal, the change in growth rates on different crystallographic facets, and the hexagonal features of the aragonite tablets led to the formation of starfruit-shaped aragonite aggregates.
Highlights
Biogenic calcium carbonate (CaCO3) has attracted considerable scientific interest because of its outstanding mechanical properties and widespread distribution in nature
The dicarboxylic amino acids, aspartic acid (Asp) and glutamic acid (Glu), had the highest content and accounted for 12.43% and 11.87% of the total, respectively (Table 1). This result is similar to a previous report, which showed a high content of Asp and Glu from the proteins within the siphon sheath inner layer (SSIL) of Lutraria lutraria [34]
Starfruit-shaped aragonite aggregates were synthesized without any additives, and a gelatinous siphon sheath from the bivalve L. sieboldii was used as the substrate
Summary
Biogenic calcium carbonate (CaCO3) has attracted considerable scientific interest because of its outstanding mechanical properties and widespread distribution in nature. The most common approach for these experiments is to use various substrates, such as chitin [15,16,17], collagen, silk fibroin [18,19,20], fibrous protein, gelatin [21,22,23,24], and nacre [25,26,27], to modulate the formation of CaCO3 polymorphs. The semitransparent siphon sheath is divided into two layers: a thin, slightly sclerotized outer layer, which is similar to the periostracum, and a transparent, colorless inner layer with a swollen, gelatinous texture. This sheath is likely acting as the template for the nucleation and growth of the CaCO3 for the shell. The transformation from ACC to aragonite is likely a universal phenomenon that exists in in vitro experiments [6, 21] and in natural nacre growth [3,4,5]
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