Since calcium carbonate is one of the most abundant biogenic minerals found in nature, it is no surprise that there has been a huge focus on its formation and use. In this review, we intend to cover the use of amorphous calcium carbonate, which is the most unstable polymorph of calcium carbonate, for the design of new materials. Amorphous calcium carbonate has been used to manipulate the morphology of new materials, and to create strong inorganic/organic hybrid materials based on biological examples. The exoskeletons of crustaceans, sea shell nacre, and brittle star eyes are a few of the examples discussed here, and researchers have looked at these biominerals for the design of new materials. By using polymer additives and organic synthetic layers to substitute for the natural proteins used in biological systems, interesting hybrid materials have been developed. By taking inspiration from this research, new ideas for the design of the fusion materials can be achieved.

Amorphous calcium carbonate (ACC) stabilized by acidic macromolecules is a useful material for the development of environmentally friendly composites. In this study, we synthesized transparent and mechanically tough ACC-based composite materials by the incorporation of water-dispersible cellulose derivatives, namely, carboxymethyl cellulose (CMC) and surface-modified crystalline cellulose nanofibers (CNFs). A solution mixing method used in the present work proved to be a powerful and efficient method for the production of mechanically tough and environmentally friendly materials. Molecular-scale interactions between carboxyl groups and Ca 2+ ions induce homogeneous dispersion of CNFs in the composites, and this gives composite films with high transparency and high mechanical properties. The composite films of CMC, CNFs, and ACC at the mixture ratios of 40, 40, and 20 wt %, showed high mechanical properties of 15.8 ± 0.93 GPa for the Young’s modulus and 268 ± 20 MPa for the tensile strength. These designed materials that are based on ACC may open up new opportunities in many fields in applications that require the use of environmentally friendly, biodegradable, mechanically tough, and transparent composite materials.

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The cover picture shows the use of amorphous calcium carbonate (ACC), found in biological organisms such as sea urchins, crayfish and nacre in sea shells, for the creation of new inorganic/organic hybrid materials. Inspired by these biological examples, and by the use of polymer additives such as polyacrylic acid (PAA) and organic synthetic layers as a substitute for the proteins present in biomaterials, interesting new materials such as patterned films, templated structures and strong hybrid composite materials were formed. Details are given in the Review by Takashi Kato and co‐workers on page 107 in Issue 1, 2017 (DOI: 10.1002/cplu.201600457).

Hybrid thin films based on an environmentally friendly biopolymer, β-chitin and zinc hydroxide carbonate were developed through a biomineralization-inspired approach.