Biomimetic CaCO3 Mineralization using Designer Molecules and Interfaces

Coir fibre-reinforced concrete for enhanced compressive strength and sustainability in construction applications

This research explores the potential of coir fibre as a sustainable and effective reinforcement material to enhance the compressive strength (CS) of concrete. The influence of the fibre volume fraction (FVF) and fibre length (FL) on the CS of the coir fibre reinforced concrete was studied using the response surface method (RSM). The selected range for the FVF was from 4 % to 12 %, and the FL varied from 0.4 cm to 1.2 cm, as per the experimental design. The research determined that the coir fibre with an FVF of 4 % and an FL of 10 mm yielded the maximum CS for the reinforced concrete cubes, measuring 34 N/mm2. Furthermore, an increase in fibre content was observed to lead to a decrease in the workability of coir fibre-reinforced concrete. Furthermore, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses of the control and coir fibres extracted from the concrete cubes after a period of 1 year indicated no significant changes in the functional properties, thermal properties and crystallinity of the fibres.

A molecular view of peptoid-induced acceleration of calcite growth

The extensive deposits of calcium carbonate (CaCO3) generated by marine organisms constitute the largest and oldest carbon dioxide (CO2) reservoir. These organisms utilize macromolecules like peptides and proteins to facilitate the nucleation and growth of carbonate minerals, serving as an effective method for CO2 sequestration. However, the precise mechanisms behind this process remain elusive. In this study, we report the use of sequence-defined peptoids, a class of peptidomimetics, to achieve the accelerated calcite step growth kinetics with the molecular level mechanistic understanding. By designing peptoids with hydrophilic and hydrophobic blocks, we systematically investigated the acceleration in step growth rate of calcite crystals using in situ atomic force microscopy (AFM), varying peptoid sequences and concentrations, CaCO3 supersaturations, and the ratio of Ca2+/ HCO3-. Mechanistic studies using NMR, three-dimensional fast force mapping (3D FFM), and isothermal titration calorimetry (ITC) were conducted to reveal the interactions of peptoids with Ca2+ and HCO3- ions in solution, as well as the effect of peptoids on solvation and energetics of calcite crystal surface. Our results indicate the multiple roles of peptoid in facilitating HCO3- deprotonation, Ca2+ desolvation, and the disruption of interfacial hydration layers of the calcite surface, which collectively contribute to a peptoid-induced acceleration of calcite growth. These findings provide guidelines for future design of sequence-specific biomimetic polymers as crystallization promoters, offering potential applications in environmental remediation (such as CO2 sequestration), biomedical engineering, and energy storage where fast crystallization is preferred.

Kinetics of Calcite Nucleation onto Sulfated Chitosan Derivatives and Implications for Water-Polysaccharide Interactions during Crystallization of Sparingly Soluble Salts

Anionic macromolecules are found at sites of CaCO3 biomineralization in diverse organisms, but their roles in crystallization are not well-understood. We prepared a series of sulfated chitosan derivatives with varied positions and degrees of sulfation, DS(SO3 -), and measured calcite nucleation rate onto these materials. Fitting the classical nucleation theory model to the kinetic data reveals the interfacial free energy of the calcite-polysaccharide-solution system, γnet, is lowest for nonsulfated controls and increases with DS(SO3 -). The kinetic prefactor also increases with DS(SO3 -). Simulations of Ca2+-H2O-chitosan systems show greater water structuring around sulfate groups compared to uncharged substituents, independent of sulfate location. Ca2+-SO3 - interactions are solvent-separated by distances that are inversely correlated with DS(SO3 -) of the polysaccharide. The simulations also predict SO3 - and NH3 + groups affect the solvation waters and HCO3 - ions associated with Ca2+. Integrating the experimental and computational evidence suggests sulfate groups influence nucleation by increasing the difficulty of displacing near-surface water, thereby increasing γnet. By correlating γnet and net charge per monosaccharide for diverse polysaccharides, we suggest the solvent-separated interactions of functional groups with Ca2+ influence thermodynamic and kinetic components to crystallization by similar solvent-dominated processes. The findings reiterate the importance of establishing water structure and properties at macromolecule-solution interfaces.

Hybrid protein microspheres and their responsive release behaviors and inhibitory effects on melanin synthesis

In this study, the formation of protein microspheres through lysosomal enzyme-assisted biomineralized crystallization was demonstrated. Spherical micro-sized hybrid CaCO3 constructs were synthesized and characterized using field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and particle size analysis. Additionally, parameters such as the Brunauer-Emmett-Teller surface area and single-point total pore volume, and adsorption/desorption analysis were used to investigate the mesoporous properties, which are advantageous for lysosomal enzyme (LE) loading. A LE can be used as an organic template, not only as a morphological controller but also for entrapping LE during the crystallization pathway. The hybrid protein microspheres accommodated 2.3 mg of LE with a 57% encapsulation efficiency and 5.1 wt% loading. The peroxidase activity of the microspheres was calculated and found to be approximately 0.0238 mM-1 min-1. pH-responsive release of the LE from CaCO3 was observed, suggesting potential biomedical and cosmetic applications in acidic environments. The hybrid LE microsphere treatment significantly alleviated melanin production in a dose-dependent manner and further downregulated the mRNA expression of MITF, tyrosinase, TYRP-1, and TYRP-2. These results indicate skin-whitening effects by inhibiting melanin without inducing cytotoxicity. The data provide the first evidence of the potential use of a LE for obtaining hybrid minerals and the effectiveness of biomineralization-based sustainable delivery of enzyme-based vehicles based on organelle-extract-assisted biomineralization.

The dynamic nature of natural and fatty acid modified calcite surfaces

Calcium carbonate, particularly in the form of calcite, is an abundant mineral widely used in both human-made products and biological systems. The calcite surface possesses a high surface energy, making it susceptible to the adsorption of organic contaminants. Moreover, the surface is also reactive towards a range of chemicals, including water. Consequently, studying and maintaining a clean and stable calcite surface is only possible under ultrahigh vacuum conditions and for limited amounts of time. When exposed to air or solution, the calcite surface undergoes rapid transformations, demanding a comprehensive understanding of the properties of calcite surfaces in different environments. Similarly, attention must also be directed towards the kinetics of changes, whether induced by fluctuating environments or at constant condition. All these aspects are encompassed in the expression "dynamic nature", and are of crucial importance in the context of the diverse applications of calcite. In many instances, the calcite surface is modified by adsorption of fatty acids to impart a desired nonpolar character. Although the binding between carboxylic acid groups and calcite surfaces is strong, the fatty acid layer used for surface modification undergoes significant alterations when exposed to water vapour and liquid water droplets. Therefore, it is also crucial to understand the dynamic nature of the adsorbed layer. This review article provides a comprehensive overview of the current understanding of both the dynamics of the calcite surface as well as when modified by fatty acid surface treatments.

Light-driven nucleation, growth, and patterning of biorelevant crystals using resonant near-infrared laser heating

Spatiotemporal control over crystal nucleation and growth is of fundamental interest for understanding how organisms assemble high-performance biominerals, and holds relevance for manufacturing of functional materials. Many methods have been developed towards static or global control, however gaining simultaneously dynamic and local control over crystallization remains challenging. Here, we show spatiotemporal control over crystallization of retrograde (inverse) soluble compounds induced by locally heating water using near-infrared (NIR) laser light. We modulate the NIR light intensity to start, steer, and stop crystallization of calcium carbonate and laser-write with micrometer precision. Tailoring the crystallization conditions overcomes the inherently stochastic crystallization behavior and enables positioning single crystals of vaterite, calcite, and aragonite. We demonstrate straightforward extension of these principles toward other biorelevant compounds by patterning barium-, strontium-, and calcium carbonate, as well as strontium sulfate and calcium phosphate. Since many important compounds exhibit retrograde solubility behavior, NIR-induced heating may enable light-controlled crystallization with precise spatiotemporal control.

Quercetin directed transformation of calcium carbonate into porous calcite and their application as delivery system for future foods

The hierarchically porous property of CaCO3 has attracted considerable attention in the field of active delivery ingredients due to its high adsorption capacity. Here, a facile and high-efficient approach to control the calcification processes of CaCO3 ending with calcite microparticles with superior porosity and stability is reported and evaluated. In this work, a series of quercetin promoted CaCO3 microparticles, using soy protein isolate (SPI) as entrapment agent, was synthesized, characterized, and their digestive behavior and antibacterial activity were evaluated. Results obtained indicated that quercetin showed good ability to direct the calcification pathway of amorphous calcium carbonate (ACC) with the formation of flower- and petal-like structures. The quercetin-loaded CaCO3 microparticles (QCM) had a macro-meso-micropore structure, which was identified to be the calcite form. The macro-meso-micropore structure provided QCM with the largest surface area of 78.984 m2g-1. The loading ratio of SPI to QCM was up to 200.94 μg per mg of QCM. The protein and quercetin composite microparticles (PQM) were produced by simply dissolving the CaCO3 core, and the obtained PQM was used for the delivery of quercetin and protein. Thermogravimetric analysis showed PQM presented with good thermal stability without the CaCO3 core. Furthermore, minor discrepancy was noted in protein conformational structures after removing the CaCO3 core. In vitro digestion revealed that approximately 80% of the loaded quercetin was released from PQM during intestinal digestion, and the released quercetin exhibited efficient transportation across the Caco-2 cell monolayer. More importantly, the PQM digesta retained enhanced antibacterial activities to inhibit growth of Escherichia coli and Staphylococcus aureus. Porous calcites show a high potential as a delivery system for food applications.

Probing pH-Dependent Dehydration Dynamics of Mg and Ca Cations in Aqueous Solutions with Multi-Level Quantum Mechanics/Molecular Dynamics Simulations

The dehydration of aqueous calcium and magnesium cations is the most fundamental process controlling their reactivity in chemical and biological phenomena, such as the formation of ionic solids or passing through ion channels. It holds particular relevance in light of recent advancements in the development of carbon capture techniques that rely on mineralization for long-term carbon storage. Specifically, dehydration of Ca2+ and Mg2+ is a key step in proposed carbon capture processes aiming to exploit the relatively high concentration of dissolved carbon dioxide in seawater via the formation of carbonate minerals from solvated Ca2+ and Mg2+ cations for sequestration and storage. Nevertheless, atomic-scale understanding of the dehydration of aqueous Ca2+ and Mg2+ cations remains limited. Here, we utilize rare event sampling via density functional theory molecular dynamics and embedded wavefunction theory calculations to elucidate the dehydration dynamics of aqueous Ca2+ and Mg2+. Emphasis is placed on the investigation of the effect pH has on the stability of the different coordination environments. Our results reveal significant differences in the dehydration dynamics of the two cations and provide insight into how they may be modulated by pH changes.

Embedding Hierarchical Pores by Mechanochemistry in Carbonates with Superior Chemoselective Catalysis and Stability

Hierarchical porosity of carbonates can facilitate their performance in massive applications as compared to their corresponding bulk samples. Traditional solution-based precipitation is typically utilized to fabricate porous carbonates. However, this tactic is generally employed under humid conditions, which demand soluble metal precursors, solvents, and extended dry periods. A salt-assisted mechanochemistry is exploited in contemporary work to settle the shortcomings. Enlighted by solid-state technology, this approach eliminates the utilization of solvents, and the process of ball milling can create pores in 5 min. A range of highly porous carbonates and their derivatives are acquired, with several materials surpassing recording surface areas (e.g., H-CaCO3: 108 m2/g, SrCO3: 125 m2/g, BaCO3: 172 m2/g, Pd/H-CaCO3 catalyst: 101 m2/g). The results display that Pd/H-CaCO3 shows superior catalytic efficiency in the synthesis of aniline (turnover frequency [TON] = 1.33 × 104/h-1, yield ≥ 99%, and recycle stability: 11 cycles) and dye degradation. Combining mechanochemistry and salt-assisted tactic provides a facile and efficient pathway for processing porous materials.

Chitosan as a Canvas for Studies of Macromolecular Controls on CaCO3 Biological Crystallization

A mechanistic understanding of how macromolecules, typically as an organic matrix, nucleate and grow crystals to produce functional biomineral structures remains elusive. Advances in structural biology indicate that polysaccharides (e.g., chitin) and negatively charged proteoglycans (due to carboxyl, sulfate, and phosphate groups) are ubiquitous in biocrystallization settings and play greater roles than currently recognized. This review highlights studies of CaCO₃ crystallization onto chitinous materials and demonstrates that a broader understanding of macromolecular controls on mineralization has not emerged. With recent advances in biopolymer chemistry, it is now possible to prepare chitosan-based hydrogels with tailored functional group compositions. By deploying these characterized compounds in hypothesis-based studies of nucleation rate, quantitative relationships between energy barrier to crystallization, macromolecule composition, and solvent structuring can be determined. This foundational knowledge will help researchers understand composition-structure-function controls on mineralization in living systems and tune the designs of new materials for advanced applications.

Secondary Structure of DNA Aptamer Influences Biomimetic Mineralization of Calcium Carbonate

Calcium materials, such as calcium carbonate, are produced in natural and industrial settings that range from oceanic to biomedical. An array of biological and biomimetic template molecules have been employed in controlling and understanding the mineralization reaction but have largely focused on small molecule additives or disordered polyelectrolytes. DNA aptamers are synthetic and programmable biomolecules with polyelectrolyte characteristics but with predictable and controllable secondary structure akin to native extracellular moieties. This work demonstrates for the first time the influence of DNA aptamers with known G-quadruplex structures on calcium carbonate mineralization. Aptamers demonstrate kinetic inhibition of mineral formation, sequence and pH-dependent uptake into the mineral, and morphological control of the primarily calcite material in controlled solution conditions. In reactions initiated from the complex matrix of ocean water, DNA aptamers demonstrated enhancement of mineralization kinetics and resulting amorphous material. This work provides new biomimetic tools to employ in controlled mineralization and demonstrates the influence that template secondary structure can have in material formation.

Calcium carbonate: controlled synthesis, surface functionalization, and nanostructured materials

Calcium carbonate (CaCO₃) is an important inorganic mineral in biological and geological systems. Traditionally, it is widely used in plastics, papermaking, ink, building materials, textiles, cosmetics, and food. Over the last decade, there has been rapid development in the controlled synthesis and surface modification of CaCO₃, the stabilization of amorphous CaCO₃ (ACC), and CaCO₃-based nanostructured materials. In this review, the controlled synthesis of CaCO₃ is first examined, including Ca²⁺-CO₃^2- systems, solid-liquid-gas carbonation, water-in-oil reverse emulsions, and biomineralization. Advancing insights into the nucleation and crystallization of CaCO₃ have led to the development of efficient routes towards the controlled synthesis of CaCO₃ with specific sizes, morphologies, and polymorphs. Recently-developed surface modification methods of CaCO₃ include organic and inorganic modifications, as well as intensified surface reactions. The resultant CaCO₃ can then be further engineered via template-induced biomineralization and layer-by-layer assembly into porous, hollow, or core-shell organic-inorganic nanocomposites. The introduction of CaCO₃ into nanostructured materials has led to a significant improvement in the mechanical, optical, magnetic, and catalytic properties of such materials, with the resultant CaCO₃-based nanostructured materials showing great potential for use in biomaterials and biomedicine, environmental remediation, and energy production and storage. The influences that the preparation conditions and additives have on ACC preparation and stabilization are also discussed. Studies indicate that ACC can be used to construct environmentally-friendly hybrid films, supramolecular hydrogels, and drug vehicles. Finally, the existing challenges and future directions of the controlled synthesis and functionalization of CaCO₃ and its expanding applications are highlighted.

Reinforcing hydrogels with in situ formed amorphous CaCO3

Hydrogels are often employed for tissue engineering and moistening applications. However, they are rarely used for load-bearing purposes because of their limited stiffness and the stiffness-toughness compromise inherent to them. By contrast, nature uses hydrogel-based materials as scaffolds for load-bearing and protecting materials by mineralizing them. Inspired by nature, the stiffness or toughness of synthetic hydrogels has been increased by forming minerals, such as CaCO₃, within them. However, the degree of hydrogel reinforcement achieved with CaCO₃ remains limited. To address this limitation, we form CaCO₃ biominerals in situ within a model hydrogel, poly(acrylamide) (PAM), and systematically investigate the influence of the size, structure, and morphology of the reinforcing CaCO₃ on the mechanical properties of the resulting hydrogels. We demonstrate that especially the structure of CaCO₃ and its affinity to the hydrogel matrix strongly influence the mechanical properties of mineralized hydrogels. For example, while the fracture energy of PAM hydrogels is increased 3-fold if reinforced with individual micro-sized CaCO₃ crystals, it increases by a factor of 13 if reinforced with a percolating amorphous calcium carbonate (ACC) nano-structure that forms in the presence of a sufficient quantity of Mg²⁺. If PAM is further functionalized with acrylic acid (AA) that possesses a high affinity towards ACC, the stiffness of the hydrogel increases by a factor 50. These fundamental insights on the structure-mechanical property relationship of hydrogels that have been functionalized with in situ formed minerals has the potential to enable tuning the mechanical properties of mineralized hydrogels over a much wider range than what is currently possible.

Stable Binding Conformations of Polymaleic and Polyacrylic Acids at a Calcite Surface in the Presence of Countercations: A Metadynamics Study

Elucidating the stable binding conformations of additives at the surface of CaCO3 crystals is essential to biomineralization, scale inhibition, and materials technology. However, accomplishing this by experimental means is rather difficult. In this study, molecular dynamics simulations based on a metadynamics approach were conducted to elucidate the stable binding conformations of a deprotonated polymaleic acid (PMA) additive and two deprotonated poly(acrylic acid) (PAA) additives with different polymerization degrees in the presence of various countercations at a hydrated calcite (104) surface. The simulated free-energy surfaces suggested the existence of several slightly different stable binding conformations for each additive. The appearance of these distinct binding conformations is speculated to originate from different balances of interactions between the additive, the calcite surface, and the countercations. The binding conformations and binding stabilities at the calcite surface were affected by the countercations, with Ca2+ ions producing a more pronounced effect than Na+ ions. Furthermore, the simulation results suggested that the binding stability at the calcite surface was higher for the PMA additive than for the PAA additives, and the PAA additive with a polymerization degree of 10 displayed a binding stability that was similar to or lower than that of the PAA additive with a polymerization degree of 5. The present simulation method provides a new strategy for analyzing the binding conformations of complex additives at material surfaces, developing additives that stably bind to these surfaces, and designing additives to control crystal growth.

Impact of Adsorption of Straight Chain Alcohol Molecules on the Optical Properties of Calcite (10.4) Surface

Calcium carbonate plays a central role in controlling the chemistry of the oceans, biomineralization and oil production, to name a few. In this work, using density functional theory with semiempirical dispersion corrections and simplified TD-DFT using Tamm-Dancoff approximation, we investigated the impact of the adsorption of straight chain alcohol (ethanol and pentanol) molecules on the optical properties of a calcite (10.4) surface. Our results show that ethanol and/or pentanol molecules form a well-ordered monolayer (through their hydroxyl group with carbon chains sticking away in a standing-up position) on the calcite (10.4) surface. Additionally, we found intriguing modulations in the photoabsorption spectra and circular dichroism spectra. In particular, the latter was a unique optical fingerprint for a molecule-adsorbed calcite (10.4) surface. Our findings provide useful insights into the structural and optical features of calcite-based systems at the atomic level.

Modification of Surfaces with Vaterite CaCO3 Particles

Former studies have demonstrated a strong interest toward the crystallization of CaCO3 polymorphs in solution. Nowadays, CaCO3 crystallization on solid surfaces is extensively being studied using biomolecules as substrates for the control of the growth aiming at various applications of CaCO3. Calcium carbonate exists in an amorphous state, as three anhydrous polymorphs (aragonite, calcite and vaterite), and as two hydrated polymorphs (monohydrocalcite and ikaite). The vaterite polymorph is considered as one of the most attractive forms due to its large surface area, biocompatibility, mesoporous nature, and other features. Based on physical or chemical immobilization approaches, vaterite can be grown directly on solid surfaces using various (bio)molecules, including synthetic polymers, biomacromolecules such as proteins and peptides, carbohydrates, fibers, extracellular matrix components, and even biological cells such as bacteria. Herein, the progress on the modification of solid surfaces by vaterite CaCO3 crystals is reviewed, focusing on main findings and the mechanism of vaterite growth initiated by various substances mentioned above, as well as the discussion of the applications of such modified surfaces.

Lignin-Induced CaCO3 Vaterite Structure for Biocatalytic Artificial Photosynthesis

The vaterite phase of CaCO₃ exhibits unique characteristics, such as high porosity, surface area, dispersivity, and low specific gravity, but it is the most unstable polymorph. Here, we report lignin-induced stable vaterite as a support matrix for integrated artificial photosynthesis through the encapsulation of key active components such as the photosensitizer (eosin y, EY) and redox enzyme (l-glutamate dehydrogenase, GDH). The lignin-vaterite/EY/GDH photobiocatalytic platform enabled the regeneration of the reduced nicotinamide cofactor under visible light and facilitated the rapid conversion of α-ketoglutarate into l-glutamate (initial conversion rate, 0.41 mM h^-1; turnover frequency, 1060 h^-1; and turnover number, 39,750). The lignin-induced vaterite structure allowed for long-term protection and recycling of the active components while facilitating the photosynthesis reaction due to the redox-active lignin. Succession of stability tests demonstrated a significant improvement of GDH's robustness in the lignin-vaterite structure against harsh environments. This work provides a simple approach for solar-to-chemical conversion using a sustainable, integrated light-harvesting system.

Distribution of Biominerals and Mineral-Organic Composites in Plant Trichomes

Biomineralization is a common phenomenon in plants and has been shown to be chemically, functionally and topologically diverse. Silica and calcium carbonate have long been known as structural plant biominerals and calcium phosphate (apatite)–long known from animals–has recently been reported. Strikingly, up to three different biominerals may occur in a single trichome in, e.g., Urticaceae and Loasaceae, and in combination with organic compounds, can form organic/inorganic composite materials. This article presents an extension of previous studies on the distribution of these biominerals in Loasaceae trichomes with a focus on their spatial (three-dimensional) distribution and co-localization with organic substances. Light microscopy and scanning electron microscopy with high-resolution EDX element analyses of sample surfaces and sections illustrate the differential distribution and composition of the different biomineral phases across cell surfaces and cell walls. Raman spectroscopy additionally permits the identification of organic and inorganic compounds side by side. All three biominerals may be found in a nearly pure inorganic phase, e.g., on the plant surfaces and in the barbs of the glochidiate trichomes, or in combination with a larger proportion of organic compounds (cellulose, pectin). The cell lumen may be additionally filled with amorphous mineral deposits. Water-solubility of the mineral fractions differs considerably. Plant trichomes provide an exciting model system for biomineralization and enable the in-vivo study of the formation of complex composite materials with different biomineral and organic compounds involved.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

Calcium carbonate particles: synthesis, temperature and time influence on the size, shape, phase, and their impact on cell hydroxyapatite formation

To develop materials for drug delivery and tissue engineering and to study their efficiency with respect to ossification, it is necessary to apply physicochemical and biological analyses. The major challenge is labor-intensive data mining during synthesis and the reproducibility of the obtained data. In this work, we investigated the influence of time and temperature on the reaction yield, the reaction rate, and the size, shape, and phase of the obtained product in the completely controllable synthesis of calcium carbonate. We show that calcium carbonate particles can be synthesized in large quantities, i.e., in gram quantities, which is a substantial advantage over previously reported synthesis methods. We demonstrated that the presence of vaterite particles can dramatically stimulate hydroxyapatite (HA) production by providing the continued release of the main HA component - calcium ions - depending on the following particle parameters: size, shape, and phase. To understand the key parameters influencing the efficiency of HA production by cells, we created a predictive model by means of principal component analysis. We found that smaller particles in the vaterite state are best suited for HA growth (HA growth was 8 times greater than that in the control). We also found that the reported dependence of cell adhesion on colloidal particles can be extended to other types of particles that contain calcium ions.

Biomineralized separation, concentration, and evaluation of the effectiveness of Schisandra chinensis fruit extract

Here, we detail the biomineralization-assisted separation and concentration of crude food extract and an evaluation of its effectiveness. Schisandra chinensis fruit extract was used as a model plant extract. Hybrid grape-like mineral was assembled by calcium carbonate mineralization. The hybrid particles of S. chinensis mineral were fully characterized using field emission scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and particle size analysis. Data including the Brunauer-Emmett-Teller surface area, single point total pore volume, and adsorption/desorption analysis of pore size were also investigated. Organic molecules, including lipids such as palmitic acid, stearic acid, and linolenic acid in the Schisandra chinensis fruit, affect the formation of complex structures involving the CaCO₃ mineralization pathway by inhibiting crystallization. However, the cosmetic active primary components were entrapped in a similar proportion in the preserved extract, and were efficiently separated without additional filtering and concentration steps for purification. In addition, the hybrid mineral was enriched (10.5 times) in Gomisin N, a representative component of S. chinensis fruit, relative to its concentration in the initial extract samples. The hybrid mineral inhibited both intracellular and extracellular melanin production and increased the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. The data provide the first evidence of the potential use of fruit extract for obtaining hybrid minerals and the effectiveness of the biomineralization-based separation and concentration strategy.

Capturing the Moment of Emergence of Crystal Nucleus from Disorder

Crystallization is the process of atoms or molecules forming an organized solid via nucleation and growth. Being intrinsically stochastic, the research at an atomistic level has been a huge experimental challenge. We report herein in situ detection of a crystal nucleus forming during nucleation/growth of a NaCl nanocrystal, as video recorded in the interior of a vibrating conical carbon nanotube at 20-40 ms frame^-1 with localization precision of <0.1 nm. We saw NaCl units assembled to form a cluster fluctuating between featureless and semiordered states, which suddenly formed a crystal. Subsequent crystal growth at 298 K and shrinkage at 473 K took place also in a stochastic manner. Productive contributions of the graphitic surface and its mechanical vibration have been experimentally indicated.

DNA nanostructures as templates for biomineralization

Nature uses extracellular matrix scaffolds to organize biominerals into hierarchical structures over various length scales. This has inspired the design of biomimetic mineralization scaffolds, with DNA nanostructures being among the most promising. DNA nanotechnology makes use of molecular recognition to controllably give 1D, 2D and 3D nanostructures. The control we have over these structures makes them attractive templates for the synthesis of mineralized tissues, such as bones and teeth. In this Review, we first summarize recent work on the crystallization processes and structural features of biominerals on the nanoscale. We then describe self-assembled DNA nanostructures and come to the intersection of these two themes: recent applications of DNA templates in nanoscale biomineralization, a crucial process to regenerate mineralized tissues.

Modulation of the CaCO3 phase and morphology by tuning the sequence of addition: an insight into the formation of monohydrocalcite

Detailed study on the formation of monohydrocalcite as well as the modulation of the CaCO3 phase and morphology.

The Crystallization Process of Vaterite Microdisc Mesocrystals via Proto-Vaterite Amorphous Calcium Carbonate Characterized by Cryo-X-ray Absorption Spectroscopy

Investigation on the formation mechanism of crystals via amorphous precursors has attracted a lot of interests in the last years. The formation mechanism of thermodynamically meta-stable vaterite in pure alcohols in the absence of any additive is less known. Herein, the crystallization process of vaterite microdisc mesocrystals via proto-vaterite amorphous calcium carbonate (ACC) in isopropanol was tracked by using Ca K-edge X-ray absorption spectroscopy (XAS) characterization under cryo-condition. Ca K-edge X-ray absorption near edge structure (XANES) spectra show that the absorption edges of the Ca ions of the vaterite samples with different crystallization times shift to lower photoelectron energy while increasing the crystallization times from 0.5 to 20 d, indicating the increase of crystallinity degree of calcium carbonate. Ca K-edge extended X-ray absorption fine structure (EXAFS) spectra exhibit that the coordination number of the nearest neighbor atom O around Ca increases slowly with the increase of crystallization time and tends to be stable as 4.3 (±1.4). Crystallization time dependent XANES and EXAFS analyses indicate that short-range ordered structure in proto-vaterite ACC gradually transform to long-range ordered structure in vaterite microdisc mesocrystals via a non-classical crystallization mechanism.

Stabilized Amorphous Calcium Carbonate as a Precursor of Microcoating on Calcite

Highly controlled biomineralization of calcium carbonate is via non-classical mesocrystallization of amorphous precursors. In the present study, a simple in vitro assay was developed to mimic the biological process, which involved stabilized amorphous calcium carbonate and a single crystal substrate of calcite. The microcoating layer formed on the calcite substrate displayed mesocrystalline characteristics, and the layers near the substrate were strongly influenced by the epitaxy to the substrate. This behavior was preserved even when the morphology of the coating layer was modified with poly(acrylic acid), a model anionic macromolecule. Interestingly, the extent of the epitaxy increased substantially with poly(ethylene imine), which barely affected the crystal morphology. The in vitro assay in the present study will be useful in the investigations of the biomineralization and bioinspired crystallization of calcium carbonate in general.

Resilient Intracrystalline Occlusions: A Solid-State NMR View of Local Structure as It Tunes Bulk Lattice Properties

In many marine organisms, biomineralization-the crystallization of calcium-based ionic lattices-demonstrates how regulated processes optimize for diverse functions, often via incorporation of agents from the precipitation medium. We study a model system consisting of l-aspartic acid (Asp) which when added to the precipitation solution of calcium carbonate crystallizes the thermodynamically disfavored polymorph vaterite. Though vaterite is at best only kinetically stable, that stability is tunable, as vaterite grown with Asp at high concentration is both thermally and temporally stable, while vaterite grown at 10-fold lower Asp concentration, yet 2-fold less in the crystal, spontaneously transforms to calcite. Solid-state NMR shows that Asp is sparsely occluded within vaterite and calcite. CP-REDOR NMR reveals that each Asp is embedded in a perturbed occlusion shell of ∼8 disordered carbonates which bridge to the bulk. In both the as-deposited vaterites and the evolved calcite, the perturbed shell contains two sets of carbonate species distinguished by their proximity to the amine and identifiable based on 13C chemical shifts. The embedding shell and the occluded Asp act as an integral until which minimally rearranges even as the bulk undergoes extensive reorganization. The resilience of these occlusion units suggests that large Asp-free domains drive the vaterite to calcite transformation-which are retarded by the occlusion units, resulting in concentration-dependent lattice stability. Understanding the structure and properties of the occlusion unit, uniquely amenable to ssNMR, thus appears to be a key to explaining other macroscopic properties, such as hardness.

Chemical evidence of rare porphyrins in purple shells of Crassostrea gigas oyster

The colour of oyster shells is a very diverse characteristic morphotype, forming intriguing vivid patterns both on the inside and outside of the shell. In the present study, we have identified for the first time, the presence of several porphyrins as constituents of the shell pigmentation of the Crassostrea gigas oyster consumed worldwide. The precise molecular structures of halochromic, fluorescent and acid-soluble porphyrins, such as uroporphyrin and turacin, are unambiguously determined by reverse phase liquid chromatography combined with high resolution mass spectrometry. Their presence account for the purple colouration of shells but also for the dark colouration of adductor muscle scars. We have also defined the endogenous origin of these porphyrins, specifically secreted or accumulated by the shell forming tissue. These findings are pioneering analytical proofs of the existence of the haem pathway in the edible oyster Crassostrea gigas, evidenced by the chemical identification of haem side-products and supported by the recent publication of the corresponding oyster genome.

Spatiotemporal control of calcium carbonate nucleation using mechanical deformations of elastic surfaces

Biological systems generate crystalline materials with properties and morphologies that cannot be duplicated using synthetic procedures. Developing strategies that mimic the control mechanisms found in nature would enhance the range of functional materials available for numerous technological applications. Herein, a biomimetic approach based on the mechano-dynamic chemistry of silicone surfaces was used to control the rate of heterogeneous CaCO3 nucleation. Specifically, stretching the silicone surface redistributed functional groups, tuning interfacial energy and thus the rate of CaCO3 crystal formation, as predicted by classical nucleation rate laws. We extended this procedure using microrelief patterns to program surface strain fields to spatially control the location of nucleation. The strategies presented herein represent a fundamental departure from traditional bottom-up crystal engineering, where surfaces are chemically static, to them being active participants in the nucleation process controlling the outcome both spatially and temporally.

Beyond carbon capture towards resource recovery and utilization: fluidized-bed homogeneous granulation of calcium carbonate from captured CO2

Atmospheric carbon dioxide (CO₂) imbalance due to anthropogenic emissions has direct impact in climate change. Recent advancements in the mitigation of industrial CO₂ emissions have been brought about by a paradigm shift from mere CO₂ capture onto various adsorbents to CO₂ conversion into high value products. The present study proposes a system which involves the conversion of CO₂ into high purity, low moisture, compact and large CaCO₃ solids through homogeneous granulation in a fluidized-bed reactor (FBR). In the present study, synthetic solutions of potassium carbonate (K₂CO₃) and calcium hydroxide (Ca(OH)₂) were used as sources of carbonate and precipitant, respectively. The effects of the degree of supersaturation (S) as chemical loading and influx flow rate (Q_T) as hydraulic loading on CaCO₃ granulation efficiency were investigated. In the study, S was varied from 10.2 to 10.8 and Q_T from 40 to 80 mL min^-1 while the operating pH and calcium-is-to-carbonate molar ratio ([Ca²⁺]/[CO₃^2-]) were set at 10 ± 0.2 and 1.50, respectively. Results showed that carbonate ions end product distribution had a highest carbonate granulation efficiency at [Carbonate]_G of 95-96% using S of 10.6 and Q_T of 60 mL min^-1. Characterization of the granules confirmed high purity calcium carbonate. Overall, the transformation of industrial CO₂ emissions into a valuable solid product can be a significant move towards the mitigation of climate change from anthropogenic emissions.

Wettability of Calcite Surfaces: Impacts of Brine Ionic Composition and Oil Phase Polarity at Elevated Temperature and Pressure Conditions

The interactions among the polar components of oil, aqueous phase ions, and carbonate minerals, as well as their subsequent effects on surface wettability, can significantly impact the fluid distribution and recovery in a hydrocarbon reservoir. In this study, we investigate the adsorption/desorption of molecules from oils with different levels of polarity on calcite surfaces during different displacement processes under elevated pressure and temperature conditions. We measured dynamic contact angles (CA) on untreated and aged calcite substrates using brines with different salinities and compositions and model oils, that is, mixtures of varying concentrations of stearic acid (SA) and n-decane. In particular, the impacts of the concentrations of Ca²⁺, SO₄^2-, and OH^- ions on the adsorption phenomena were explored. For the nonpolar oil, increasing brine salinity or removing Ca²⁺ ions from the aqueous phase impacted the potentials of oil-brine and brine-mineral interfaces and shifted the wettability of calcite surface toward more water-wet conditions. In the presence of polar oil, the adsorption of the polar components controls the surface wettability. Higher concentrations of Ca²⁺/SO₄^2- could facilitate/obstruct the polar component adsorption and thus increase/decrease the dynamic oil-water CAs. It is also observed that the brine salinity does not impact the wettability if excess SA is added to the oil phase, that is, if the oil phase is strongly polar. Moreover, the adsorption of SA on the calcite surface under experimental conditions is found to be reversible during the displacement events. The surface energy calculation for the adsorption process indicates that the surface coverage of calcite by SA is more sensitive to the presence of Ca²⁺ in brine than the concentration of polar components in oil. We also conducted several experiments on calcite substrates aged with SA. The measurements demonstrate that the adsorbed SA molecules are detached when the aged mineral surface is exposed to a lower-salinity brine at high temperatures, and the SA molecules could be adsorbed back on the surface once the displacement is halted.

3D Chitin Scaffolds of Marine Demosponge Origin for Biomimetic Mollusk Hemolymph-Associated Biomineralization Ex-Vivo

Structure-based tissue engineering requires large-scale 3D cell/tissue manufacture technologies, to produce biologically active scaffolds. Special attention is currently paid to naturally pre-designed scaffolds found in skeletons of marine sponges, which represent a renewable resource of biomaterials. Here, an innovative approach to the production of mineralized scaffolds of natural origin is proposed. For the first time, a method to obtain calcium carbonate deposition ex vivo, using living mollusks hemolymph and a marine-sponge-derived template, is specifically described. For this purpose, the marine sponge Aplysin aarcheri and the terrestrial snail Cornu aspersum were selected as appropriate 3D chitinous scaffold and as hemolymph donor, respectively. The formation of calcium-based phase on the surface of chitinous matrix after its immersion into hemolymph was confirmed by Alizarin Red staining. A direct role of mollusks hemocytes is proposed in the creation of fine-tuned microenvironment necessary for calcification ex vivo. The X-ray diffraction pattern of the sample showed a high CaCO3 amorphous content. Raman spectroscopy evidenced also a crystalline component, with spectra corresponding to biogenic calcite. This study resulted in the development of a new biomimetic product based on ex vivo synthetized ACC and calcite tightly bound to the surface of 3D sponge chitin structure.

Calcium cyclic carboxylates as structural models for calcium carbonate scale inhibitors

Calcium complexes of cyclic oligocarboxylic acids have been studied as models to understand how subtle changes in molecular structure lead to significant variation in inhibition ability for calcium carbonate deposition

Unexpected discovery of calcium cryptates with exceptional stability

A 2,2′-bipyridine-N,N′-dioxide-based cryptand has been found to exhibit exceptional apparent complex stability for Ca²⁺and unusually shows very high selectivity for Ca²⁺over trivalent lanthanoid cations.

Thermal properties and surface chemistry of cotton varieties mineralized with calcium carbonate polymorphs by cyclic dipping

In this study, hydroentangled cotton nonwovens were identified as effective hosts for mineralization of calcium carbonate (CaCO₃) polymorphs to modify and improve their properties. All cotton varieties studied, including raw white cotton, scoured white cotton, and raw brown cotton, readily crystallized CaCO₃via a simple cyclic dipping process. A combination of analyses agreed that the surface chemistry of cotton fibers influenced the formation of different CaCO₃ polymorphs. Scoured white cotton that consisted of almost pure cellulose predominantly produced the most stable calcite, whereas raw white and raw brown cottons that contain proteins facilitated the production of partial metastable vaterite. The morphology of calcite was better defined on the scoured cotton. The mineralization altered the hydrophobic surface of raw cottons to be hydrophilic, i.e., two-fold increase in moisture regain and decrease in water contact angle from 130 to 0 degrees. The mineralized cottons also exhibited improved thermal resistance, i.e., slower thermal decomposition with decreased activation energies and reduction in heat release capacity by up to 40%.

Hydroentangled nonwovens of raw white cotton fiber, scoured white cotton fiber, and raw brown cotton fiber are effective hosts for mineralization of calcium carbonate polymorphs to modify and improve their thermal and surface properties.

Water: How Does It Influence the CaCO3 Formation?

Nature produces biomineral-based materials with a fascinating set of properties using only a limited number of elements. This set of properties is obtained by closely controlling the structure and local composition of the biominerals. We are far from achieving the same degree of control over the properties of synthetic biomineral-based composites. One reason for this inferior control is our incomplete understanding of the influence of the synthesis conditions and additives on the structure and composition of the forming biominerals. In this Review, we provide an overview of the current understanding of the influence of synthesis conditions and additives during different formation stages of CaCO₃ , one of the most abundant biominerals, on the structure, composition, and properties of the resulting CaCO₃ crystals. In addition, we summarize currently known means to tune these parameters. Throughout the Review, we put special emphasis on the role of water in mediating the formation of CaCO₃ and thereby influencing its structure and properties, an often overlooked aspect that is of high relevance.

Anisotropy in Stable Conformations of Hydroxylate Ions between the {001} and {110} Planes of TiO2 Rutile Crystals for Glycolate, Lactate, and 2-Hydroxybutyrate Ions Studied by Metadynamics Method

Control over TiO2 rutile crystal growth and morphology using additives is essential for the development of functional materials. Computer simulation studies on the thermodynamically stable conformations of additives at the surfaces of rutile crystals contribute to understanding the mechanisms underlying this control. In this study, a metadynamics method was combined with molecular dynamics simulations to investigate the thermodynamically stable conformations of glycolate, lactate, and 2-hydroxybutyrate ions at the {001} and {110} planes of rutile crystals. Two simple atom-atom distances were selected as collective variables for the metadynamics method. At the {001} plane, a conformation in which the COO- group was oriented toward the surface was found to be the most stable for the lactate and 2-hydroxybutyrate ions, whereas a conformation in which the COO- group was oriented toward water was the most stable for the glycolate ion. At the {110} plane, a conformation in which the COO- group was oriented toward the surface was the most stable for all three hydroxylate ions, and a second most stable conformation was also observed for the lactate ion at positions close to the {110} plane. For all three hydroxylate ions (α-hydroxycarboxylate ions), the stability of the most stable conformation was higher for the {110} plane than for the {001} plane. At both planes, the stability of the most stable conformation was highest for the 2-hydroxybutyrate ion and lowest for the glycolate ion. Supposing that all three hydroxylate ions serve to decrease the surface free energy at the rutile surface and that a more stable conformation at the rutile surface leads to a greater decrease in the surface free energy, the present results partially explain experimentally observed differences in the changes in growth rate and morphology of rutile crystals in the presence of glycolic, lactic, and 2-hydroxybutyric acids.

Calcium Carbonate Mineralization in a Surface-Tension-Confined Droplets Array

Calcium carbonate biomimetic crystallization remains a topic of interest with respect to biomineralization areas in recent research. It is not easy to conduct high-throughput experiments with only a few macromolecule reagents using conventional experimental methods. However, the emergence of microdroplet array technology provides the possibility to solve these issues efficiently. In this article, surface-tension-confined droplet arrays were used to fabricate calcium carbonate. It was found that calcium carbonate crystallization can be conducted in surface-tension-confined droplets. Defects were found on the surface of some crystals, which were caused by liquid flow inside the droplet and the rapid drop in droplet height during the evaporation. The diameter and number of crystals were related to the droplet diameter. Polyacrylic acid (PAA), added as a modified organic molecule control, changed the CaCO3 morphology from calcite to vaterite. The material products of the above experiments were compared with bulk-synthesized calcium carbonate by scanning electron microscopy (SEM), Raman spectroscopy and other characterization methods. Our work proves the possibility of performing biomimetic crystallization and biomineralization experiments on surface-tension-confined microdroplet arrays.

Hierarchy of Hybrid Materials-The Place of Inorganics-in-Organics in it, Their Composition and Applications

Hybrid materials, or hybrids incorporating both organic and inorganic constituents, are emerging as a very potent and promising class of materials due to the diverse, but complementary nature of the properties inherent of these different classes of materials. The complementarity leads to a perfect synergy of properties of desired material and eventually an end-product. The diversity of resultant properties and materials used in the construction of hybrids, leads to a very broad range of application areas generated by engaging very different research communities. We provide here a general classification of hybrid materials, wherein organics-in-inorganics (inorganic materials modified by organic moieties) are distinguished from inorganics-in-organics (organic materials or matrices modified by inorganic constituents). In the former area, the surface functionalization of colloids is distinguished as a stand-alone sub-area. The latter area-functionalization of organic materials by inorganic additives-is the focus of the current review. Inorganic constituents, often in the form of small particles or structures, are made of minerals, clays, semiconductors, metals, carbons, and ceramics. They are shown to be incorporated into organic matrices, which can be distinguished as two classes: chemical and biological. Chemical organic matrices include coatings, vehicles and capsules assembled into: hydrogels, layer-by-layer assembly, polymer brushes, block co-polymers and other assemblies. Biological organic matrices encompass bio-molecules (lipids, polysaccharides, proteins and enzymes, and nucleic acids) as well as higher level organisms: cells, bacteria, and microorganisms. In addition to providing details of the above classification and analysis of the composition of hybrids, we also highlight some antagonistic yin-&-yang properties of organic and inorganic materials, review applications and provide an outlook to emerging trends.

Synergistic Effect of Granular Seed Substrates and Soluble Additives in Structural Control of Prismatic CaCO3 Thin Films

In biomineralization and bioinspired mineralization, substrates and additives function synergistically in providing structural control of the mineralized layers including their orientation, polymorph, morphology, hierarchical architecture, etc. Herein, a novel type of granular aragonitic CaCO₃-poly(acrylic acid) substrate guides the mineralization of prismatic CaCO₃ thin films of distinct morphology and polymorph in the presence of different additives including organic compounds and polymers. For instance, weakly charged amino acids lead to columnar aragonite overlayers, while their charged counterparts and organic acids/bases inhibit the overgrowth. Employment of several specific soluble polymer additives in overgrowth instead results in calcitic overlayers with distinct hierarchical architecture, good hardness/Young's modulus, and under-water superoleophobicity. Interestingly, self-organized patterns in the CaCO₃-poly(l-glutamic acid) overlayer are obtained under proper mineralization conditions. We demonstrate that the granular seed comprised of mineralized and polymeric constituents is a versatile platform for obtaining prismatic CaCO₃ thin films, where structural control can be realized by the employment of different types of additives in overgrowth. We expect the methodology to be applied to a broad spectrum of bioinspired, prismatic-type crystalline products, aiming for the development of high-performance hybrids.