Biomimetic Synthesis of Macroscopic-Scale Calcium Carbonate Thin Films. Evidence for a Multistep Assembly Process

Abstract

Biologically controlled mineralization features an orchestrated balance among various controlling factors such as spatial delineation, template promotion, crystal growth modification and cessation, and so on. Highly ordered calcium carbonate lamellae formed in the nacreous layers of mollusk (aragonite), the foliated calcitic layers of mollusk (calcite), or the semi-nacre of brachiopods (calcite) are excellent examples of the outcome of such synergistic control. Mimicking the concerted interplay of template promotion and growth inhibition as often utilized in biomineralization, we have synthesized macroscopic and continuous calcium carbonate thin films with thickness ranging from 0.4 to 0.6 μm. The thin films were prepared at air/subphase interfaces by promoting mineral deposition with amphiphilic porphyrin templates, coupled with growth inhibition by the use of poly(acrylic acid) as a soluble inhibitor. Films formed at 22 °C were found to have a biphasic structure containing both amorphous and crystalline calcium carbonate. The crystalline regions were identified to be calcite oriented with the (00.1) face parallel to the porphyrin monolayer at the air/subphase interface. Films obtained in the early stage of formation at lower temperature (4 °C) displayed characteristics of a single amorphous phase. These observations suggest that films formed through a multistage assembly process, during which an initial amorphous deposition was followed by a phase transformation into the ultimate crystalline phase and the orientation of the crystalline phase was controlled by the porphyrin template during the phase transformation. The results provide new insights into the template-inhibitor−biomineral interaction and a new mechanism for synthesizing ceramic thin film under mild conditions.

Novel Basic Protein, PfN23, Functions as Key Macromolecule during Nacre Formation

“…In Vitro Calcium Carbonate Crystallization Assay-Saturated calcium bicarbonate solution was prepared following the method of Xu et al (39), with some modifications. CO 2 gas was bubbled through the mixture of calcium carbonate and Milli-Q deionized water for 6 h, and the excess solid CaCO 3 was removed by filtration.…”

Polarization-dependent imaging contrast in abalone shells

“…Aragonite accounts for 95% of nacre's mass, leading one to expect the mechanical characteristics of nacre to be similar to those of aragonite, yet nacre is 3000 times more resistant to fracture than aragonite (6). Materials scientists have only recently began to learn how to prepare synthetic composites outperforming their components by such large factors, and do so inspired by nacre (7,8,9,10), although not as efficiently and orderly organized as natural nacre. It is therefore of extreme interest to understand and possibly harness the mechanisms of nacre formation.…”

The Biomimetic Mineralization Closer to a Real Biomineralization

“…The Ca 2+ ions in (104) plane has the similar structure of orthogonal repeat units to the -helix conformation, which provides convenience for their structural regulation to grow along the (104) plane, while the template and structural adaptability play a key role in the oriented crystallization of CaCO 3 ). In the experiments, the transformation of calcium carbonate from unstable amorphous calcium carbonate (ACC) phase to stable calcite crystals was also observed, indicating a multistep crystallization process found in other biomimetic mineralization of calcium carbonate crystals (Xu, et al, 1998;Pouget, et al, 2009). Fig.…”