Biomimetic mineralization of calcium carbonate: modulation of crystal morphology by sticky rice amylopectin in the Ca2+-HCO3- system

Biomineralization is a prevalent and fundamental phenomenon observed in nature. During mineralization, the remarkable specificity and dynamic modulatory capabilities of organic molecules enable the precise control over both the type and structure of minerals at the microscopic level. Drawing inspiration from biomineralization and naturally high concentration of bicarbonate ions in ecosystem waters, this study investigates the biomimetic mineralization process of calcium carbonate within the CaCl2-sticky rice (SR)-NaHCO3 system. Specifically, it examines the effects of SR concentration and calcium ions concentration on the morphology and structure of calcium carbonate crystals. The findings reveal that SR amylopectin, as an organic polysaccharide, effectively influences both the morphology and particle size of calcium carbonate crystals during their crystallization process. The most pronounced modulatory effect is observed at a SR concentration of 0.5 wt%, with a Ca2+: HCO3- molar concentration ratio of 1:4. By providing nucleating coordination sites for calcium carbonate, SR amylopectin facilitates the binding of calcium ions with carbonate ions, thereby promoting the formation of calcium carbonate with an ordered and mineralized structure. The concentration of SR determines the degree of tightness in the branched chain connections within the SR amylopectin structure. When the structural connections are moderately tight and the calcium ions concentration is low, multiple hydroxyl groups within the amylopectin structure coordinate with the same calcium ion. This coordination promotes the uniform growth of calcium carbonate in all directions during the nucleation process, ultimately resulting in the formation of spherical calcium carbonate particles. However, under conditions of high calcium ion concentration, the number of coordination sites becomes insufficient, and the phenomenon of calcium ions being adsorbed by multiple hydroxyl groups within the branched chains weakens. This ultimately results in the formation of cubic-shaped, monocrystalline calcium carbonate particles. The findings can provide a theoretical basis for the practical engineering applications of biomimetic mineralization technologies in bicarbonate-rich environments.

Ultrafast, cytocompatible mineralization of calcium phosphate in the formation of stratified nanoshells of artificial spores

Spatially controlled confinement of catalytic enzymes within nanoshells holds substantial potential for applications in bioreactors, synthetic cells, and artificial spores. The utilization of amorphous calcium phosphate (CaP) precursors enables the extremely rapid (<5 seconds) construction of thick (∼400 nm) CaP nanoshells, stratified with distinct enzymes, on various tannic acid-primed substrates. Saccharomyces cerevisiae cells are nanoencapsulated with enzyme-embedded, multilayered CaP nanoshells in a cytocompatible manner, providing an advanced chemical tool for interfacing living cells with functional entities in a spatially controlled configuration.

Affinity for OH- Produces Four-Coordinated Zn2+ Impurities in Hydrated Amorphous Calcium Carbonate

Using ab initio based molecular dynamics and electronic structure calculations, we show that Zn impurities in hydrated amorphous calcium carbonate (ACC) have a much lower coordination number than other divalent impurities due to covalent interactions between the 3d Zn shell and the oxygen atoms of the carbonate and water groups. The local structure around Zn in ACC, including the predicted low coordination number, is confirmed by X-ray absorption spectroscopy of synthetic Zn-bearing ACC. The strong Zn-O chemical interaction leads to substantial water dissociation and slightly disrupts the hydrogen bonding network. Implications of Zn2+ incorporation for ACC stability are discussed.

Stabilization and crystallization mechanism of amorphous calcium carbonate

Amorphous phases hold great promise in diverse applications and are widely used by organisms as precursors to produce biominerals with complex morphologies and excellent properties. However, the stabilization and crystallization mechanisms of amorphous phases are not fully understood, especially in the presence of additives. Here, using amorphous calcium carbonate (ACC) as the model system, we systematically investigate the crystallization pathways of amorphous phases in the presence of poly(Aspartic acid) (pAsp) with various chain lengths. Results show that pure ACC transforms into a mixture of calcite and vaterite via the typical dissolution-recrystallization mechanism and 3 % of Asp monomer exhibits negligible effect. However, pAsp with a chain length of only 10 strongly inhibits the aggregation-induced formation of vaterite spheres while slightly delaying the growth of calcite via classical ion-by-ion attachment, thus kinetically favoring the formation of calcite. Moreover, the inhibition effect of calcite growth from solution ions becomes more prominent with the increase of pAsp chain length or concentration, which significantly improves the stability of the amorphous phase and leads to crystallization of spherical or elongated calcite via the nonclassical particle attachment mechanism after pseudomorphic transformation of ACC into vaterite nanoparticles. These results allow us to reach a more comprehensive understanding of the stabilization and crystallization mechanism of ACC in the presence of additives and provide guidelines for controlling the polymorph selection and morphology of crystals during the crystallization of amorphous precursors.

Experimental Study on the Effect of an Organic Matrix on Improving the Strength of Tailings Strengthened by MICP

In order to improve the effect of microbial-induced calcium carbonate precipitation (MICP) in tailings reinforcement, sodium citrate, an organic matrix with good water solubility, was selected as the crystal form adjustment template for inducing calcium carbonate crystallization, and the reinforcements of tailings by MICP were conducted in several experiments. The effects of sodium citrate on the yield, crystal form, crystal appearance, and distribution of calcium carbonate were analyzed by MICP solution test; thus, the related results were obtained. These showed that the addition of a proper amount of organic matrix sodium citrate could result in an increment in the yield of calcium carbonate. The growth rate of calcium carbonate reached 22.6% under the optimum amount of sodium citrate, and the crystals of calcium carbonate were diverse and closely arranged. Based on this, the MICP reinforcement test of tailings was carried out under the action of the optimum amount of sodium citrate. The microscopic analysis using CT and other means showed that the calcium carbonate is distributed more uniformly in tailings, and the porosity of samples is significantly reduced by layered scanning analysis. The results of triaxial shear tests showed that adding organic matrix sodium citrate effectively increased the cohesion, internal friction angle, and peak stress of the reinforced tailings. It aims to provide a novel idea, a creative approach, and a method to enhance the reinforcement effect of tailings and green solidification technology in the mining environment.

Tailored hydrogel composite membrane for the regulated crystallization of monosodium urate monohydrate within coffee's metabolites system

Herein, a facile bionic research platform with fabricated hydrogel composite membrane (HCM) is constructed to uncover the effects of the main components of coffee's metabolites on MSUM crystallization. Tailored and biosafety polyethylene glycol diacrylate/N-isopropyl acrylamide (PEGDA/NIPAM) HCM allows the proper mass transfer of coffee's metabolites and can well simulate the process of coffee's metabolites acting in the joint system. With the validations of this platform, it is shown that chlorogenic acid (CGA) can hinder the MSUM crystals formation from 45 h (control group) to 122 h (2 mM CGA), which is the most likely reason that reduces the risk of gout after long-term coffee consumption. Molecular dynamics simulation further indicates that the high interaction energy (E_int) between CGA and MSUM crystal surface and the high electronegativity of CGA both contribute to the restraint of MSUM crystal formation. In conclusion, the fabricated HCM, as the core functional materials of the research platform, presents the understanding of the interaction between coffee consumption and gout control.