Shaping Amorphous Calcium Carbonate Films into 2D Model Substrates for Bone Cell Culture

Nanocrystalline and Amorphous Calcium Carbonate from Waste Seashells by Ball Milling Mechanochemistry Processes

Nanocrystalline calcium carbonate (CaCO3) and amorphous CaCO3 (ACC) are materials of increasing technological interest. Nowadays, they are mainly synthetically produced by wet reactions using CaCO3 reagents in the presence of stabilizers. However, it has recently been discovered that ACC can be produced by ball milling calcite. Calcite and/or aragonite are the mineral phases of mollusk shells, which are formed from ACC precursors. Here, we investigated the possibility to convert, on a potentially industrial scale, the biogenic CaCO3 (bCC) from waste mollusk seashells into nanocrystalline CaCO3 and ACC. Waste seashells from the aquaculture species, namely oysters (Crassostrea gigas, low-Mg calcite), scallops (Pecten jacobaeus, medium-Mg calcite), and clams (Chamelea gallina, aragonite) were used. The ball milling process was carried out by using different dispersing solvents and potential ACC stabilizers. Structural, morphological, and spectroscopic characterization techniques were used. The results showed that the mechanochemical process produced a reduction of the crystalline domain sizes and formation of ACC domains, which coexisted in microsized aggregates. Interestingly, bCC behaved differently from the geogenic CaCO3 (gCC), and upon long milling times (24 h), the ACC reconverted into crystalline phases. The aging in diverse environments of mechanochemically treated bCC produced a mixture of calcite and aragonite in a species-specific mass ratio, while the ACC from gCC converted only into calcite. In conclusion, this research showed that bCC can produce nanocrystalline CaCO3 and ACC composites or mixtures having species-specific features. These materials can enlarge the already wide fields of applications of CaCO3, which span from medical to material science.

Fabrication of patterned calcium carbonate materials through template-assisted microbially induced calcium carbonate precipitation

Patterned calcium carbonate materials with controlled morphologies have broad applications in both environmental and engineering fields. However, how to fabricate such materials through environmental-friendly methods under ambient conditions is still challenging. Here, we report a green approach for fabricating patterned calcium carbonate materials. This eco-friendly approach is based on template-assisted microbially induced calcium carbonate precipitation. As a proof of concept, by varying the templates and optimizing fabrication parameters, different patterned calcium carbonate materials were obtained. The optimized parameters include C_Ca²⁺ = 80 mM, T_i = 15 °C, and templates made of small-sized CaCO₃ particles with a concentration of 1.5 mg mL⁻¹, under which better and more sharp patterns were obtained. Materials with periodic patterns were also fabricated through a periodic template, showing good scalability of this approach. The results of this study could mean great potential in applications where spatially controlled calcium carbonate depositions with user-designed patterns are needed.

A simple and green approach based on template-assisted microbially induced calcium carbonate precipitation for the fabrication of patterned calcium carbonate materials was demonstrated.

Biomineralization as an inspiration for materials chemistry

Living organisms are well known for building a wide range of specially designed organic-inorganic hybrid materials such as bone, teeth, and shells, which are highly sophisticated in terms of their adaptation to function. This has inspired physicists, chemists, and materials scientists to mimic such structures and their properties. In this Review we describe how strategies used by nature to build and tune the properties of biominerals have been applied to the synthesis of materials for biomedical, industrial, and technological purposes. Bio-inspired approaches such as molecular templating, supramolecular templating, organized surfaces, and phage display as well as methods to replicate the structure and function of biominerals are discussed. We also show that the application of in situ techniques to study and visualize the bio-inspired materials is of paramount importance to understand, control, and optimize their preparation. Biominerals are synthesized in aqueous media under ambient conditions, and these approaches can lead to materials with a reduced ecological footprint than can traditional methods.