Biomimetic synthesis of oriented aragonite crystals and nacre-like composite material by controlling the fluid type

Chitosan as a Canvas for Studies of Macromolecular Controls on CaCO3 Biological Crystallization

A mechanistic understanding of how macromolecules, typically as an organic matrix, nucleate and grow crystals to produce functional biomineral structures remains elusive. Advances in structural biology indicate that polysaccharides (e.g., chitin) and negatively charged proteoglycans (due to carboxyl, sulfate, and phosphate groups) are ubiquitous in biocrystallization settings and play greater roles than currently recognized. This review highlights studies of CaCO₃ crystallization onto chitinous materials and demonstrates that a broader understanding of macromolecular controls on mineralization has not emerged. With recent advances in biopolymer chemistry, it is now possible to prepare chitosan-based hydrogels with tailored functional group compositions. By deploying these characterized compounds in hypothesis-based studies of nucleation rate, quantitative relationships between energy barrier to crystallization, macromolecule composition, and solvent structuring can be determined. This foundational knowledge will help researchers understand composition-structure-function controls on mineralization in living systems and tune the designs of new materials for advanced applications.

Revisiting the role of calcite in Spondylus crassisquama shell

Spondylus crassisquama (princeps) is a bivalve mollusc inhabiting the coast of Central and South Americas. Its shell uses a two-layer armour system to protect the inner soft tissues from the environment. The external layer is composed of a calcite-based composite, and the internal layer is composed of an aragonite-based composite. For the first time, the structural characterisation of the S. crassisquama shell is reported. The results show similarities with those for other shells such as that of red abalone. As expected, microhardness tests demonstrate that the internal nacreous layer is stiffer and harder than the external calcitic layer. However, the amount of energy dissipated during the indentation tests of the calcitic layer is similar to the amount of energy dissipated by the nacreous layers. Despite the highly ordered structure of the nacreous layer, the characterisation conducted shows that the calcitic layer can also be used as a model for the development of bioinspired materials.