Surface-Induced Coacervation Facilitates Localized Precipitation of Mineral Precursors from Dilute Solutions

Abstract

Many organisms orchestrate the controlled precipitation of minerals. This physiological process takes place at ambient conditions, using soluble ions as building blocks. A widespread strategy for such crystallization processes is using a multistep route, where the initial phase is metastable and gradually transforms into the mature mineral phase. Even though the maturation of these intermediate phases has been intensively studied, it remains unclear how the initial, far from equilibrium phase can form within the cellular context. A model system for controlled biomineralization is the production of coccoliths by marine microalgae. Coccoliths are calcium carbonate crystalline arrays that form within the intracellular environment, at very low calcium concentrations. Here, we used coccolith-derived and synthetic polymers to study, in vitro, the chemical interactions between calcium ions and organic macromolecules that precede coccolith formation. We used in situ analyses, including state-of-the-art cryo-electron tomography and liquid-cell atomic force microscopy, to study the interactions in bulk solution and on organic surfaces simultaneously. The results unveil a chemical process in which a functional surface induces the precipitation of a polymer–Ca dense phase, or a coacervate, at chemical conditions where precipitation in solution is kinetically inhibited. This strategy demonstrates how organisms can form dense Ca-rich phases from the submillimolar concentration of calcium within organelles. This Ca-rich phase can then transform into a mineral precursor in a subsequent step, without posing challenges to cellular homeostasis.

Insight on the Role of Poly(acrylic acid) for Directing Calcium Phosphate Mineralization of Synthetic Polymer Bone Scaffolds

“…The coating theory could also explain why PAA 1.8 additive demonstrates a greater kinetic delay of mineral, since lower molecular weight PAA would be expected to cover a greater surface area on the NFSKs. Krounbi et al recently reported that PAA- co -maleic acid in a Ca 2+ solution will precipitate as a polymer-Ca coacervate onto a coccolith base plate at conditions that preclude precipitation in solution, suggesting that the functionalized surface itself can template the coacervate deposition . In our current work, we do not see evidence of a dense surface coacervate under TEM, but the NFSKs could act as a substrate for the deposition of a thin polymer layer, slowing intra-kebab mineralization.…”

Modulating ion-binding at macromolecular interfaces during (bio)mineralization: A snapshot review for calcium carbonate and calcium phosphate systems

“…In-situ cryoTEM studies have recently shown how coccolith base plates associate with natural and synthetic carboxylated macromolecules to assemble Ca 2+ at the coccolith base plate surface which decreases Ca 2+ concentration in solution (Fig. 3) [66]. Vesicles within the coccolithophore-often also composed of or containing charged polysaccharides-then transport ions to mineralization locales [67].…”

Bio-Inspired 3D Printing of Layered Structures Utilizing Stabilized Amorphous Calcium Carbonate within Biodegradable Matrices

“…The obtained PDI is higher than expected for a monodispersed distribution in all samples, which can be explained by the ACC instability and the tendency of the particles to agglomerate. [39] Table 3 -DLS measurements of ACC and 3D printed models, illustrating changes in particle size before and after the oven drying stage. results compared to the 50 50 ⁄ CGN15% model.…”