Oriented Growth of Calcite Controlled by Self-Assembled Monolayers of Functionalized Alkanethiols Supported on Gold and Silver

Spatioselective Occlusion of Copolymer Nanoparticles within Calcite Crystals Generates Organic-Inorganic Hybrid Materials with Controlled Internal Structures

Efficient occlusion of particulate additives into a single crystal has garnered an ever-increasing attention in materials science because it offers a counter-intuitive yet powerful platform to make crystalline nanocomposite materials with emerging properties. However, precisely controlling the spatial distribution of the guest additives within a host crystal remains highly challenging. We herein demonstrate a unique, straightforward method to engineer the spatial distribution of copolymer nanoparticles within calcite (CaCO3) single crystals by judiciously adjusting initial [Ca2+] concentration used for the calcite precipitation. More specifically, polymerization-induced self-assembly is employed to synthesize well-defined and highly anionic poly(3-sulfopropyl methacrylate potassium)41-block-poly(benzyl methacrylate)500 [PSPMA41-PBzMA500] diblock copolymer nanoparticles, which are subsequently used as model additives during the growth of calcite crystals. Impressively, such guest nanoparticles are preferentially occluded into specific regions of calcite depending on the initial [Ca2+] concentration. These unprecedented phenomena are most probably caused by dynamic change in electrostatic interaction between Ca2+ ions and PSPMA41 chains based on systematic investigations. This study not only showcases a significant advancement in controlling the spatial distribution of guest nanoparticles within host crystals, enabling the internal structure of composite crystals to be rationally tailored via a spatioselective occlusion strategy, but also provides new insights into biomineralization.

Directing polymorph specific calcium carbonate formation with de novo protein templates

Biomolecules modulate inorganic crystallization to generate hierarchically structured biominerals, but the atomic structure of the organic-inorganic interfaces that regulate mineralization remain largely unknown. We hypothesized that heterogeneous nucleation of calcium carbonate could be achieved by a structured flat molecular template that pre-organizes calcium ions on its surface. To test this hypothesis, we design helical repeat proteins (DHRs) displaying regularly spaced carboxylate arrays on their surfaces and find that both protein monomers and protein-Ca2+ supramolecular assemblies directly nucleate nano-calcite with non-natural {110} or {202} faces while vaterite, which forms first in the absence of the proteins, is bypassed. These protein-stabilized nanocrystals then assemble by oriented attachment into calcite mesocrystals. We find further that nanocrystal size and polymorph can be tuned by varying the length and surface chemistry of the designed protein templates. Thus, bio-mineralization can be programmed using de novo protein design, providing a route to next-generation hybrid materials.

A Nanoparticle-Based Model System for the Study of Heterogeneous Nucleation Phenomena

Heterogeneous nucleation processes are involved in many important phenomena in nature, including devastating human diseases caused by amyloid structures or the harmful frost formed on fruits. However, understanding them is challenging due to the difficulties of characterizing the initial stages of the process occurring at the interface between the nucleation medium and the substrate surfaces. This work implements a model system based on gold nanoparticles to investigate the effect of particle surface chemistry and substrate properties on heterogeneous nucleation processes. Using widely available techniques such as UV-vis-NIR spectroscopy and light microscopy, gold nanoparticle-based superstructure formation was studied in the presence of substrates with different hydrophilicity and electrostatic charges. The results were evaluated on grounds of classical nucleation theory (CNT) to reveal kinetic and thermodynamic contributions of the heterogeneous nucleation process. In contrast to nucleation from ions, the kinetic contributions toward nucleation turned out to be larger than the thermodynamic contributions for the nanoparticle building blocks. Electrostatic interactions between substrates and nanoparticles with opposite charges were crucial to enhancing the nucleation rates and decreasing the nucleation barrier of superstructure formation. Thereby, the described strategy is demonstrated advantageous for characterizing physicochemical aspects of heterogeneous nucleation processes in a simple and accessible manner, which could be potentially explored to study more complex nucleation phenomena.

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.

Morphological Evolution of Calcite Grown in Zwitterionic Hydrogels: Charge Effects Enhanced by Gel-Incorporation

The incorporation of charged biomacromolecules is widely found in biomineralization. To investigate the significance of this biological strategy for mineralization control, gelatin-incorporated calcite crystals grown from gelatin hydrogels with different charge concentrations along the gel networks are examined. It is found that the bound charged groups on gelatin networks (amino cations, gelatin-NH₃ ⁺ and carboxylic anions, gelatin-COO^- ) play crucial roles in controlling the single-crystallinity and the crystal morphology. And the charge effects are greatly enhanced by the gel-incorporation because the incorporated gel networks force the bound charged groups on them to attach to crystallization fronts. In contrast, ammonium ions (NH₄ ⁺ ) and acetate ions (Ac^- ) dissolve in the crystallization media do not exhibit the similar charge effects because the balance of attachment/detachment make them more difficult to be incorporated. Employing the revealed charge effects, the calcite crystal composites with different morphologies can be flexibly prepared.

Matrix-Directed Mineralization for Bulk Structural Materials

Mineral-based bulk structural materials (MBSMs) are known for their long history and extensive range of usage. The inherent brittleness of minerals poses a major problem to the performance of MBSMs. To overcome this problem, design principles have been extracted from natural biominerals, in which the extraordinary mechanical performance is achieved via the hierarchical organization of minerals and organics. Nevertheless, precise and efficient fabrication of MBSMs with bioinspired hierarchical structures under mild conditions has long been a big challenge. This Perspective provides a panoramic view of an emerging fabrication strategy, matrix-directed mineralization, which imitates the in vivo growth of some biominerals. The advantages of the strategy are revealed by comparatively analyzing the conventional fabrication techniques of artificial hierarchically structured MBSMs and the biomineral growth processes. By introducing recent advances, we demonstrate that this strategy can be used to fabricate artificial MBSMs with hierarchical structures. Particular attention is paid to the mass transport and the precursors that are involved in the mineralization process. We hope this Perspective can provide some inspiring viewpoints on the importance of biomimetic mineralization in material fabrication and thereby spur the biomimetic fabrication of high-performance MBSMs.

Role of Mass Transport in the Deposition, Growth, and Transformation of Calcium Carbonate on Surfaces at High Supersaturation

We demonstrate how combined in-situ measurements and finite element method modeling can provide new insight into the relative contribution of mass transport to the growth of calcium carbonate on two model surfaces, glass and gold, under high-supersaturation conditions relevant to surface scaling. An impinging jet-radial flow system is used to create a high-supersaturated solution at the inlet of different cells: an optical microscope cell presenting a glass surface for deposition and quartz crystal microbalance (QCM) and in-situ IR spectroscopy cells, both presenting a gold surface. The approach described is quantitative due to the well-defined mass transport, and both time-lapse optical microscopy images and QCM data are analyzed to provide information on the growth kinetics of the calcite crystals. Initially, amorphous calcium carbonate (ACC), formed in solution, dominates the deposition process. At longer times, the growth of calcite is more significant and, on glass, is observed to consume ACC from the surface, leading to surface regions depleted of ACC developing around calcite microcrystals. On Au, the mass increase becomes linear with time in this region. Taken together, these microscopic and macroscopic measurements demonstrate that calcite growth has a significant component of mass transport control at high supersaturation. Finite element method (FEM) simulations of mass-transport-limited crystal growth support the strong mass transport contribution to the growth kinetics and further suggest that the observed growth must be sustained by more than just the Ca²⁺ and CO₃ ^2- in solution, with dissolution/direct attachment of ACC and/or ion pairs also contributing to the growth process.

A Polyplex in a Shell: The Effect of Poly(aspartic acid)-Mediated Calcium Carbonate Mineralization on Polyplexes Properties and Transfection Efficiency

Mineralization by exposure of organic templates to supersaturated solutions is used by many living organisms to generate specialized materials to perform structural or protective functions. Similarly, it was suggested that improved robustness acquired through mineralization under natural conditions could be an important factor for virus survival outside of a host for better transfection of cells. Here, inspired by this fact, we developed a nonviral tricomponent polyplex system for gene delivery capable of undergoing mineralization. First, we fabricated anionic polyplexes carrying pDNA by self-assembly with a lipid-modified cationic polymer and coating by poly(aspartic acid). Then, we submitted the polyplexes to a two-step mineralization reaction to precipitate CaCO₃ under various supersaturations. We carried out detailed morphological studies of the mineralized polyplexes and identified which parameters of the fabrication process were influential on transfection efficiency. We found that mineralization with CaCO₃ is efficient in promoting transfection efficiency as long as a certain Ca²⁺/CO₃^2- lower limit ratio is respected. However, calcium incubation can also be used to achieve similar effects at higher concentrations depending on polyplex composition, probably due to the formation of physical cross-links by calcium binding to poly(aspartic acid). We proposed that the improved robustness and transfection efficiency provided by means of mineralization can be used to expand the possible applications of polyplexes in gene therapy.

Mineralized vectors for gene therapy

There is an intense interest in developing materials for safe and effective delivery of polynucleotides using non-viral vectors. Mineralization of organic templates has long been used to produce complex materials with outstanding biocompatibility. However, a lack of control over mineral growth has limited the applicability of mineralized materials to a few in vitro applications. With better control over mineral growth and surface functionalization, mineralized vectors have advanced significantly in recent years. Here, we review the recent progress in chemical synthesis, physicochemical properties, and applications of mineralized materials in gene therapy, focusing on structure-function relationships. We contrast the classical understanding of the mineralization mechanism with recent ideas of mineralization. A brief introduction to gene delivery is summarized, followed by a detailed survey of current mineralized vectors. The vectors derived from calcium phosphate are articulated and compared to other minerals with unique features. Advanced mineral vectors derived from templated mineralization and specialty coatings are critically analyzed. Mineral systems beyond the co-precipitation are explored as more complex multicomponent systems. Finally, we conclude with a perspective on the future of mineralized vectors by carefully demarcating the boundaries of our knowledge and highlighting ambiguous areas in mineralized vectors. STATEMENT OF SIGNIFICANCE: Therapy by gene-based medicines is increasingly utilized to cure diseases that are not alleviated by conventional drug therapy. Gene medicines, however, rely on macromolecular nucleic acids that are too large and too hydrophilic for cellular uptake. Without tailored materials, they are not functional for therapy. One emerging class of nucleic acid delivery system is mineral-based materials. The fact that they can undergo controlled dissolution with minimal footprint in biological systems are making them attractive for clinical use, where safety is utmost importance. In this submission, we will review the emerging synthesis technology and the range of new generation minerals for use in gene medicines.

Significance of atomic-scale defects in flexible surfaces on local solvent and ion behaviour

Many factors can affect the course of heterogeneous nucleation, such as surface chemistry, flexibility and topology, substrate concentration and solubility. Atomic-scale defects are rarely investigated in detail and are often considered to be unimportant surface features. In this work, we set out to investigate the significance of atomic-scale defects in a flexible self-assembled monolayer surface for the behaviour of clusters of Ca²⁺ and CO₃^2- ions in water. To this end, we use molecular dynamics simulations to estimate the diffusion coefficients of ion clusters at different topological surface features and obtain ionic radial distribution functions around features of interest. Well-tempered metadynamics is used to gain insight into the free energy of ions around selected surface defects. We find that certain defects, which we refer to as active defects, can impair ionic surface diffusion, as well as affect the diffusion of ions in close proximity to the surface feature in question. Our findings suggest that this effect can result in an ability of such topological features to promote ion clustering and increase local ionic concentration at specific surface sites. The work reported here shows how the presence of small atomic-scale defects can affect the role of a surface in the process of heterogeneous nucleation and contributes towards a rational definition of surfaces as effective nucleating agents.

Quiescent Mineralisation for Free-standing Mineral Microfilms with a Hybrid Structure

HYPOTHESIS

The air-solution interface of supersaturated calcium hydrogen carbonate (Ca(HCO₃)₂) represents the highest saturation state due to evaporation/CO₂-degassing, where calcite crystals are expected to nucleate and grow along the interface. Hence, it should be possible to form a free-standing mineral-only calcium carbonate (CaCO₃) microfilm at the air-solution interface of Ca(HCO₃)₂. The air-solution interface of phosphate buffered saline (PBS) could represent a phase boundary to introduce a hybrid microstructure of CaCO₃ and carbonate-rich dicalcium hydroxide phosphate (carbonate-rich hydroxylapatite).

EXPERIMENTS

Supersaturated Ca(HCO₃)₂ was prepared at high pressure and heated to form CaCO₃ microfilms, which were converted to bone-like microfilms at the air-solution interface of PBS by dissolution-recrystallisation. The microfilms were characterised by scanning electron microscopy, 3D confocal microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, laser Raman microspectroscopy, and X-ray photoelectron spectroscopy. An in situ X-ray diffraction (XRD) system that simulates the aforementioned interfacial techniques was developed to elucidate the microfilms formation mechanisms.

FINDINGS

The CaCO₃ and bone-like microfilms were free-standing, contiguous, and crystalline. The bone-like microfilms exhibited a hybrid structure consisting of a surface layer of remnant calcite and a carbonate-rich hydroxylapatite core of plates. The present work shows that the air-solution interface can be used to introduce hybrid microstructures to mineral microfilms.

Extended Lifetime of Molecules Adsorbed onto Excipients Drives Nucleation in Heterogeneous Crystallization

Monte Carlo (MC) and molecular dynamics (MD) computer simulations were used to investigate the role of adsorption during seeded and heterogeneous crystallization. The simulations characterized the range of adsorption energies and configurations encountered during adsorption of individual molecules of active pharmaceutical ingredients (APIs), with varying hydrogen-bonding tendencies, onto seed and heterosurfaces. Specifically, the adsorption of acetaminophen (AAP), carbamazepine (CBMZ), fenofibrate (FF), phenylbutazone (PBZ), clozapine (CPB), and risperidone (RIS) was simulated on selected crystallographic facets of their own crystals as examples of seeded crystallizations and on lactose or microcrystalline cellulose (MCC) substrates as heterosurfaces. The MC screening provided adsorption enthalpies in the range of -59 to -155 kJ mol^-1 for these APIs on lactose, generally increasing as the molar mass of the API increased. The corresponding values predicted for adsorption of each API onto its own crystal were in the range of -92 to -201 kJ mol^-1. More detailed MD simulations performed in methanol showed adsorption free energies for RIS on MCC in the range of -37 to -50 kJ mol^-1 with strong molecule-surface complexation lifetime of tens of nanoseconds on the (010) face of MCC. This extended lifetime is a key feature in understanding the mechanism of heterogeneous crystallization. A well-formed nucleus is generated on the surface starting with a single adsorbed molecule. Individual or small clusters add to the adsorbed species. This addition is facilitated by the extended lifetime of the adsorbed molecule, which is several orders of magnitude greater than the time required for additional molecules to assemble and grow into a stable nucleus attached to the heterosurface.

Role of Self-Assembled Surface Functionalization on Nucleation Kinetics and Oriented Crystallization of a Small-Molecule Drug: Batch and Thin-Film Growth of Aspirin as a Case Study

The present paper assesses the heterogeneous nucleation of a small-molecule drug and its relationship with the surface chemistry of engineered heteronucleants. The nucleation of aspirin (ASA) was tuned by different functional groups exposed by self-assembled monolayers (SAMs) immobilized on glass surfaces. Smooth topographies and defect-free surface modification allowed the deconvolution of chemical and topographical effects on nucleation. The nucleation induction time of ASA in batch crystallization was mostly enhanced by methacrylate and amino groups, whereas it was repressed by thiol groups. In this perspective, we also present a novel strategy for the evaluation of surface-drug interactions by confining drug crystallization to thin films and studying the preferential growth of crystal planes on different surfaces. Crystallization by spin coating improved the study of oriented crystallization, enabling reproducible sample preparation, minimal amounts of drug required, and short processing time. Overall, the acid surface tension of SAMs dictated the nucleation kinetics and the extent of relative growth of the ASA crystal planes. Moreover, the face-selective action of monolayers was investigated by force spectroscopy and attributed to the preferential interaction of exposed groups with the (100) crystal plane of ASA.

Chiral and SHG-Active Metal-Organic Frameworks Formed in Solution and on Surfaces: Uniformity, Morphology Control, Oriented Growth, and Postassembly Functionalization

We demonstrate the formation of uniform and oriented metal–organic frameworks using a combination of anion effects and surface chemistry. Subtle but significant morphological changes result from the nature of the coordinative counteranion of the following metal salts: NiX₂ with X = Br^–, Cl^–, NO₃^–, and OAc^–. Crystals could be obtained in solution or by template surface growth. The latter results in truncated crystals that resemble a half structure of the solution-grown ones. The oriented surface-bound metal–organic frameworks (sMOFs) are obtained via a one-step solvothermal approach rather than in a layer-by-layer approach. The MOFs are grown on Si/SiOx substrates modified with an organic monolayer or on glass substrates covered with a transparent conductive oxide (TCO). Regardless of the different morphologies, the crystallographic packing is nearly identical and is not affected by the type of anion or by solution versus the surface chemistry. A propeller-type arrangement of the nonchiral ligands around the metal center affords a chiral structure with two geometrically different helical channels in a 2:1 ratio with the same handedness. To demonstrate the accessibility and porosity of the macroscopically oriented channels, a chromophore (resorufin sodium salt) was successfully embedded into the channels of the crystals by diffusion from solution, resulting in fluorescent crystals. These “colored” crystals displayed polarized emission (red) with a high polarization ratio because of the alignment of these dyes imposed by the crystallographic structure. A second-harmonic generation (SHG) study revealed Kleinman symmetry-forbidden nonlinear optical properties. These surface-bound and oriented SHG-active MOFs have the potential for use as single nonlinear optical (NLO) devices.

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.

Thermodynamic and Kinetic Parameters for Calcite Nucleation on Peptoid and Model Scaffolds: A Step toward Nacre Mimicry

The production of novel composite materials, assembled using biomimetic polymers known as peptoids (N-substituted glycines) to nucleate CaCO₃, can open new pathways for advanced material design. However, a better understanding of the heterogeneous CaCO₃ nucleation process is a necessary first step. We determined the thermodynamic and kinetic parameters for calcite nucleation on self-assembled monolayers (SAMs) of nanosheet-forming peptoid polymers and simpler, alkanethiol analogues. We used nucleation rate studies to determine the net interfacial free energy (γ _net) for the peptoid-calcite interface and for SAMs terminated with carboxyl headgroups, amine headgroups, or a mix of the two. We compared the results with γ _net determined from dynamic force spectroscopy (DFS) and from density functional theory (DFT), using COSMO-RS simulations. Calcite nucleation has a lower thermodynamic barrier on the peptoid surface than on carboxyl and amine SAMs. From the relationship between nucleation rate (J ₀) and saturation state, we found that under low-saturation conditions, i.e. <3.3 (pH 9.0), nucleation on the peptoid substrate was faster than that on all of the model surfaces, indicating a thermodynamic drive toward heterogeneous nucleation. When they are taken together, our results indicate that nanosheet-forming peptoid monolayers can serve as an organic template for CaCO₃ polymorph growth.

Design of Chemical Surface Treatment for Laser-Textured Metal Alloys to Achieve Extreme Wetting Behavior

Extreme wetting activities of laser-textured metal alloys have received significant interest due to their superior performance in a wide range of commercial applications and fundamental research studies. Fundamentally, extreme wettability of structured metal alloys depends on both the surface structure and surface chemistry. However, compared with the generation of physical topology on the surface, the role of surface chemistry is less explored for the laser texturing processes of metal alloys to tune the wettability. This work introduces a systematic design approach to modify the surface chemistry of laser textured metal alloys to achieve various extreme wettabilities, including superhydrophobicity/superoleophobicity, superhydrophilicity/superoleophilicity, and coexistence of superoleophobicity and superhydrophilicity. Microscale trenches are first created on the aluminum alloy 6061 surfaces by nanosecond pulse laser surface texturing. Subsequently, the textured surface is immersion-treated in several chemical solutions to attach target functional groups on the surface to achieve the final extreme wettability. Anchoring fluorinated groups (-CF₂- and -CF₃) with very low dispersive and nondispersive surface energy leads to superoleophobicity and superhydrophobicity, resulting in repelling both water and diiodomethane. Attachment of the polar nitrile (-C≡N) group with very high nondispersive and high dispersive surface energy achieves superhydrophilicity and superoleophilicity by drawing water and diiodomethane molecules in the laser-textured capillaries. At last, anchoring fluorinated groups (-CF₂- and -CF₃) and polar sodium carboxylate (-COONa) together leads to very low dispersive and very high nondispersive surface energy components. It results in the coexistence of superoleophobicity and superhydrophilicity, where the treated surface attracts water but repels diiodomethane.

Organothiol Monolayer Formation Directly on Muscovite Mica

Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X-ray diffraction, and vibrational sum-frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self-assembled into (water) stable and adaptable ultra-flat organothiol monolayers over homogenous areas as large as 1 cm2 . The strength of the mica-organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth.

A basic protein, N25, from a mollusk modifies calcium carbonate morphology and shell biomineralization

Biomineralization is a widespread biological process in the formation of shells, teeth, or bones. Matrix proteins in biominerals have been widely investigated for their roles in directing biomineralization processes such as crystal morphologies, polymorphs, and orientations. Here, we characterized a basic matrix protein, named mantle protein N25 (N25), identified previously in the Akoya pearl oyster (Pinctada fucata). Unlike some known acidic matrix proteins containing Asp or Glu as possible Ca²⁺-binding residues, we found that N25 is rich in Pro (12.4%), Ser (12.8%), and Lys (8.8%), suggesting it may perform a different function. We used the recombinant protein purified by refolding from inclusion bodies in a Ca(HCO₃)₂ supersaturation system and found that it specifically affects calcite morphologies. An X-ray powder diffraction (XRD) assay revealed that N25 could help delay the transformation of vaterites (a metastable calcium carbonate polymorph) to calcite. We also used fluorescence super-resolution imaging to map the distribution of N25 in CaCO₃ crystals and transfected a recombinant N25-EGFP vector into HEK-293T cells to mimic the native process in which N25 is secreted by mantle epithelial cells and integrated into mineral structures. Our observations suggest N25 specifically affects crystal morphologies and provide evidence that basic proteins lacking acidic groups can also direct biomineralization. We propose that the attachment of N25 to specific sites on CaCO₃ crystals may inhibit some crystal polymorphs or morphological transformation.

The Co2+/Ni2+ ion-mediated formation of a topochemically converted copper coordination polymer: structure-dependent electrocatalytic activity

The presence of Co²⁺/Ni²⁺ ions strongly influenced the formation of copper coordination polymers that showed a structure-dependent hydrogen evolution reaction catalytic activity.

Anionic Polymer Brushes for Biomimetic Calcium Phosphate Mineralization-A Surface with Application Potential in Biomaterials

This article describes the synthesis of anionic polymer brushes and their mineralization with calcium phosphate. The brushes are based on poly(3-sulfopropyl methacrylate potassium salt) providing a highly charged polymer brush surface. Homogeneous brushes with reproducible thicknesses are obtained via surface-initiated atom transfer radical polymerization. Mineralization with doubly concentrated simulated body fluid yields polymer/inorganic hybrid films containing AB-Type carbonated hydroxyapatite (CHAP), a material resembling the inorganic component of bone. Moreover, growth experiments using Dictyostelium discoideum amoebae demonstrate that the mineral-free and the mineral-containing polymer brushes have a good biocompatibility suggesting their use as biocompatible surfaces in implantology or related fields.

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.

The mechanisms of crystal growth inhibition by organic and inorganic inhibitors

Understanding mineral growth mechanism is a key to understanding biomineralisation, fossilisation and diagenesis. The presence of trace compounds affect the growth and dissolution rates and the form of the crystals produced. Organisms use ions and organic molecules to control the growth of hard parts by inhibition and enhancement. Calcite growth in the presence of Mg²⁺ is a good example. Its inhibiting role in biomineralisation is well known, but the controlling mechanisms are still debated. Here, we use a microkinetic model for a series of inorganic and organic inhibitors of calcite growth. With one, single, nonempirical parameter per inhibitor, i.e. its adsorption energy, we can quantitatively reproduce the experimental data and unambiguously establish the inhibition mechanism(s) for each inhibitor. Our results provide molecular scale insight into the processes of crystal growth and biomineralisation, and open the door for logical design of mineral growth inhibitors through computational methods.

Although trace compounds are known to inhibit crystal growth, the mechanisms by which they do so are unclear. Here, the authors use a microkinetic model to study the mechanisms of several inhibitors of calcite growth, finding that the processes are quite different for inorganic and organic inhibitors.

Occlusion of magnetic nanoparticles within calcium carbonate single crystals under external magnetic field

This work studied the growth of calcium carbonate single crystals on top of the monolayer of Fe3O4@SiO2 nanoparticles (NPs) with added external magnetic field. It showed that the occlusion process of the NPs into calcium carbonate single crystals varies as the force balance on the NPs shifts. Under no or weak magnetic field, the NPs are relatively mobile, the separation force from the substrate on NPs due to the growing calcium carbonate crystals is larger than the attraction force to the substrate by the magnetic field. The complete occlusion of the NPs into the single crystals is therefore observed. As the magnetic field strength increases, the balance shifts toward the attraction force. The mobility of NPs decreases and partial occlusion of the NPs into the single crystals is gradually observed. The findings in this study offer further insight into the occlusion process experienced by the NPs and also potential approach in engineering the force balance for the design and generation of composite materials that occlude foreign materials into their matrix.

Self-assembled monolayers of sulfonate-terminated alkanethiols investigated by frequency modulation atomic force microscopy in liquid

A molecular-scale understanding of self-assembled monolayers (SAMs) of sulfonate-terminated alkanethiols is crucial for interfacial studies of functionalized SAMs and their various applications. However, such an understanding has been difficult to achieve because of the lack of direct information on these molecular-scale structures in real space. In this study, we investigated the structures of sulfonate SAMs of sodium 11-mercapto-1-undecanesulfonate (MUS) by frequency modulation atomic force microscopy (FM-AFM) in liquid. The subnanometer-resolution FM-AFM images showed that the single-component MUS SAM prepared in pure water had random surface structures. In contrast, the MUS SAM prepared in a water-ethanol mixed solvent showed periodic striped structures with a flat-lying conformation. The results suggest a significant solvent effect on molecular-scale structures of long-chain sulfonate SAMs. In addition, we investigated the molecular-scale structures of mixed SAMs of MUS and 11-mercapto-1-undecanol (MUO) with alkane chains of the same length. The FM-AFM images of the mixed SAMs showed clear phase separation between MUS SAM and MUO SAM domains. In the MUO SAM domains, the incorporated MUS molecules appeared as protrusions. The results obtained in this study provide direct structural information on long-chain sulfonate and mixed SAMs.

Thermosensitive polymer controlled morphogenesis and phase discrimination of calcium carbonate

Homogeneous aragonite flowers with controlled surface structures can be synthesized by using a thermosensitive polymer, i.e. poly (ethylene glycol)-poly(N-isopropyl acrylamide)-poly(acrylamido methyl propane sulfonate) (PEG-PNIPAM-PAMPS), as a crystal growth modifier in the mineralization of calcium carbonate.

Spatially controlled positioning of coordination polymer nanoparticles onto heterogeneous nanostructured surfaces

Prussian Blue Analog (PBA) nanoparticles were formed on a heterogeneous nanostructured surface made of an ordered nanoperforated titanium oxide thin film deposited on a gold layer. The study of the nanocomposite film by grazing-incidence wide angle X-ray scattering, infrared spectroscopy, scanning electron microscopy and atomic force microscopy shows that the PBA particles are precisely positioned within all the perforations of the oxide film over very large surface areas. Further investigation on the formation of the PBA particles demonstrates a decisive role of a heterogeneous nucleation of the coordination polymer driven by well-adjusted surfaces energies and reactant concentrations in the spatial positioning of the PBA particles. Thanks to the well-controlled positioning of the particles within the ordered nanoperforations, the latter were successfully used as nano crucibles for the local transformation of PBA into the corresponding metal alloy by heat treatment. The thin film heterostructure thus obtained, made of ferromagnetic islands isolated by diamagnetic walls, opens interesting perspectives for the design of magnetic storage devices.

Suppression of Frost Nucleation Achieved Using the Nanoengineered Integral Humidity Sink Effect

Inhibition of frost formation is important for increasing efficiency of refrigeration systems and heat exchangers, as well as for preventing the rapid icing over of water-repellant coatings that are designed to prevent accumulation of rime and glaze. From a thermodynamic point of view, this task can be achieved by either increasing hydrophobicity of the surface or decreasing the concentration of water vapor above it. The first approach has been studied in depth, but so far has not yielded a robust solution to the problem of frost formation. In this work, we systematically explore how frost growth can be inhibited by controlling water vapor concentration using bilayer coatings with a porous exterior covering a hygroscopic liquid-infused layer. We lay the theoretical foundation and provide experimental validation of the mass transport mechanism that governs the integral humidity sink effect based on this coating platform as well as reveal intriguing sizing effects about this system. We show that the concentration profile above periodically spaced pores is governed by the sink and source concentrations and two geometrical parameters: the nondimensional pore size and the ratio of the pore spacing to the boundary layer thickness. We demonstrate that when the ratio of the pore spacing to the boundary layer thickness vanishes, as for the nanoporous bilayer coatings, the entire surface concentration becomes uniform and equal to the concentration set by the hygroscopic liquid. In other words, the surface concentration becomes completely independent of the nanopore size. We identified the threshold geometrical parameters for this condition and show that it can lead to a 65 K decrease in the nucleation onset surface temperature below the dew point. With this fundamental insight, we use bilayer coatings to nanoengineer the integral humidity sink effect to provide extreme antifrosting performance with up to a 2 h delay in nucleation onset at 263 K. The nanoporous bilayer coatings can be designed to combine optimal antifrosting functionality with a superhydrophobic water repelling exterior to provide coatings that can robustly prevent frost, rime, and glaze accumulation. By minimizing the required amount of antifreeze, this anti-icing method can have minimal operational cost and environmental impact.

Structured growth from sheaf-like nuclei to highly asymmetric morphology in poly(nonamethylene terephthalate)

Thorough microscopy analyses are done on dissecting 3D interiors of poly(nonamethylene terephthalate) (PNT) banded spherulites.

Calcium carbonate crystallisation at charged graphite surfaces

For identical solution conditions, the crystallisation of calcium carbonate (polymorph and crystal orientation) at Highly Oriented Pyrolytic Graphite substrates is highly dependent on substrate surface charge.

"Capillary-Bridge Lithography" for Patterning Organic Crystals toward Mode-Tunable Microlaser Arrays

A versatile "capillary-bridge lithography" technique is developed for patterning 1D organic single crystals and microring structures through controlling the generation and dewetting of capillary bridges on an interface with asymmetric wettability. High-performance Fabry-Pérot and whispering-gallery mode lasing emission with tunable modes are achieved on these 1D and microring structures.

The role of amino acids in hydroxyapatite mineralization

Polar and charged amino acids (AAs) are heavily expressed in non-collagenous proteins (NCPs), and are involved in hydroxyapatite (HA) mineralization in bone. Here, we review what is known on the effect of single AAs on HA precipitation. Negatively charged AAs, such as aspartic acid, glutamic acid (Glu) and phosphoserine are largely expressed in NCPs and play a critical role in controlling HA nucleation and growth. Positively charged ones such as arginine (Arg) or lysine (Lys) are heavily involved in HA nucleation within extracellular matrix proteins such as collagen. Glu, Arg and Lys intake can also increase bone mineral density by stimulating growth hormone production. In vitro studies suggest that the role of AAs in controlling HA precipitation is affected by their mobility. While dissolved AAs are able to inhibit HA precipitation and growth by chelating Ca2+ and PO43- ions or binding to nuclei of calcium phosphate and preventing their further growth, AAs bound to surfaces can promote HA precipitation by attracting Ca2+ and PO43- ions and increasing the local supersaturation. Overall, the effect of AAs on HA precipitation is worth being investigated more, especially under conditions closer to the physiological ones, where the presence of other factors such as collagen, mineralization inhibitors, and cells heavily influences HA precipitation. A deeper understanding of the role of AAs in HA mineralization will increase our fundamental knowledge related to bone formation, and could lead to new therapies to improve bone regeneration in damaged tissues or cure pathological diseases caused by excessive mineralization in tissues such as cartilage, blood vessels and cardiac valves.

Evolution from Classical to Non-classical Aggregation-Based Crystal Growth of Calcite by Organic Additive Control

Aggregation-based crystal growth is distinct from the classical understanding of solution crystallization. In this study, we reveal that N-stearoyl-l-glutamic acid (C18-Glu, an amphiphile that mimics a biomineralization-relevant biomolecule) can switch calcite crystallization from a classical ion-by-ion growth to a non-classical particle-by-particle pathway, which combines the classical and non-classical crystallization in one system. This growth mechanism change is controlled by the concentration ratio of [C18-Glu]/[Ca(2+)] in solution. The high [C18-Glu]/[Ca(2+)] can stabilize precursor nanoparticles to provide building blocks for aggregation-based crystallization, in which the interaction between C18-Glu and the nanoprecursor phase rather than that of C18-Glu on calcite steps is highlighted. Our finding emphasizes the enrollment of organic additives on metastable nano building blocks, which provides an alternative understanding about organic control in inorganic crystallization.

Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.

A Chemical Template for Synthesis of Molecular Sheets of Calcium Carbonate

Inspired by the discovery of graphene and its unique properties, we focused our research to develop a scheme to create nacre like lamellar structures of molecular sheets of CaCO₃ interleaved with an organic material, namely carbon. We developed a facile, chemical template technique, using a formulation of poly(acrylic) acid (PAA) and calcium acetate to create lamellar stacks of single crystal sheets of CaCO₃, with a nominal thickness of 17 Å, the same as a unit-cell dimension for calcite (c–axis = 17.062 Å), interleaved with amorphous carbon with a nominal thickness of 8 Å. The strong binding affinity between carboxylate anions and calcium cations in the formulation was used as a molecular template to guide CaCO₃ crystallization. Computational modeling of the FTIR spectra showed good agreement with experimental data and confirmed that calcium ions are bridged between polymer chains, resulting in a net-like polymer structure. The process readily lends itself to explore the feasibility of creating molecular sheets of other important inorganic materials and potentially find applications in many fields such as super capacitors and “low k di-electric” systems.

Surface Dipole Control of Liquid Crystal Alignment

Detailed understanding and control of the intermolecular forces that govern molecular assembly are necessary to engineer structure and function at the nanoscale. Liquid crystal (LC) assembly is exceptionally sensitive to surface properties, capable of transducing nanoscale intermolecular interactions into a macroscopic optical readout. Self-assembled monolayers (SAMs) modify surface interactions and are known to influence LC alignment. Here, we exploit the different dipole magnitudes and orientations of carboranethiol and -dithiol positional isomers to deconvolve the influence of SAM-LC dipolar coupling from variations in molecular geometry, tilt, and order. Director orientations and anchoring energies are measured for LC cells employing various carboranethiol and -dithiol isomer alignment layers. The normal component of the molecular dipole in the SAM, toward or away from the underlying substrate, was found to determine the in-plane LC director orientation relative to the anisotropy axis of the surface. By using LC alignment as a probe of interaction strength, we elucidate the role of dipolar coupling of molecular monolayers to their environment in determining molecular orientations. We apply this understanding to advance the engineering of molecular interactions at the nanoscale.

Biomimetic and bio-inspired uses of mollusc shells

Climate change and ocean acidification are likely to have a profound effect on marine molluscs, which are of great ecological and economic importance. One process particularly sensitive to climate change is the formation of biominerals in mollusc shells. Fundamental research is broadening our understanding of the biomineralization process, as well as providing more informed predictions on the effects of climate change on marine molluscs. Such studies are important in their own right, but their value also extends to applied sciences. Biominerals, organic/inorganic hybrid materials with many remarkable physical and chemical properties, have been studied for decades, and the possibilities for future improved use of such materials for society are widely recognised. This article highlights the potential use of our understanding of the shell biomineralization process in novel bio-inspired and biomimetic applications. It also highlights the potential for the valorisation of shells produced as a by-product of the aquaculture industry. Studying shells and the formation of biominerals will inspire novel functional hybrid materials. It may also provide sustainable, ecologically- and economically-viable solutions to some of the problems created by current human resource exploitation.

Inhibition of Condensation Frosting by Arrays of Hygroscopic Antifreeze Drops

The formation of frost and ice can have negative impacts on travel and a variety of industrial processes and is typically addressed by dispensing antifreeze substances such as salts and glycols. Despite the popularity of this anti-icing approach, some of the intricate underlying physical mechanisms are just being unraveled. For example, recent studies have shown that in addition to suppressing ice formation within its own volume, an individual salt saturated water microdroplet forms a region of inhibited condensation and condensation frosting (RIC) in its surrounding area. This occurs because salt saturated water, like most antifreeze substances, is hygroscopic and has water vapor pressure at its surface lower than water saturation pressure at the substrate. Here, we demonstrate that for macroscopic drops of propylene glycol and salt saturated water, the absolute RIC size can remain essentially unchanged for several hours. Utilizing this observation, we demonstrate that frost formation can be completely inhibited in-between microscopic and macroscopic arrays of propylene glycol and salt saturated water drops with spacing (S) smaller than twice the radius of the RIC (δ). Furthermore, by characterizing condensation frosting dynamics around various hygroscopic drop arrays, we demonstrate that they can delay complete frosting over of the samples 1.6 to 10 times longer than films of the liquids with equivalent volume. The significant delay in onset of ice nucleation achieved by dispensing propylene glycol in drops rather than in films is likely due to uniform dilution of the drops driven by thermocapillary flow. This transport mode is absent in the films, leading to faster dilution, and with that facilitated homogeneous nucleation, near the liquid-air interface.

Polymer-Controlled Morphosynthesis and Mineralization of Metal Carbonate Superstructures (†)

Different morphosynthesis strategies for various metal carbonate minerals such as CaCO3, BaCO3, CdCO3, MnCO3, and PbCO3 using double hydrophilic block copolymers (DHBCs) as crystal modifiers are presented. The influence of the DHBCs with different functionalities such as carboxyl, partially phosphonated, and phosphorylated groups on the crystallization and structure formation was investigated. Well-defined crystals with size range from mesoscale to microscale can be easily obtained. More complex higher-order superstructures such as hollow spheres and big spherules with controlled surface structures can also be assembled conveniently. The results show that polymer-controlled mineralization is a versatile tool toward crystal morphogenesis. A time-dependent self-assembly and growth of "sphere-to-rod-to-dumbbell-to-sphere" structures was observed in the case of BaCO3 under the control of DHBCs, adding to the already reported examples of CaCO3 and fluoroapatite. In addition, we found that the influence of the DHBCs while increasing the ionic strength was lost in case of CaCO3, implying that the strong selective interaction between the functional groups of DHBCs and crystals has electrostatic contributions.

Two competitive nucleation mechanisms of calcium carbonate biomineralization in response to surface functionality in low calcium ion concentration solution

Four self-assembled monolayer surfaces terminated with –COOH, –OH, –NH₂ and –CH₃ functional groups are used to direct the biomineralization processes of calcium carbonate (CaCO₃) in low Ca²⁺ concentration, and the mechanism of nucleation and initial crystallization within 12 h was further explored. On −COOH surface, nucleation occurs mainly via ion aggregation mechanism while prenucleation ions clusters may be also involved. On −OH and −NH₂ surfaces, however, nucleation forms via calcium carbonate clusters, which aggregate in solution and then are adsorbed onto surfaces following with nucleation of amorphous calcium carbonate (ACC). Furthermore, strongly negative-charged −COOH surface facilitates the direct formation of calcites, and the −OH and −NH₂ surfaces determine the formation of vaterites with preferred crystalline orientations. Neither ACC nor crystalline CaCO₃ is observed on −CH₃ surface. Our findings present a valuable model to understand the CaCO₃ biomineralization pathway in natural system where functional groups composition plays a determining role during calcium carbonate crystallization.

Metal-organic framework membranes: from synthesis to separation application

Metal-organic framework (MOF) materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers, exhibit regular crystalline lattices with relatively well-defined pore structures and interesting properties. As a new class of porous solid materials, MOFs are attractive for a variety of industrial applications including separation membranes - a rapidly developing research area. Many reports have discussed the synthesis and applications of MOFs and MOF thin films, but relatively few have addressed MOF membranes. This critical review provides an overview of the diverse MOF membranes that have been prepared, beginning with a brief introduction to the current techniques for the fabrication of MOF membranes. Gas and liquid separation applications with different MOF membranes are also included (175 references).

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials: organic molecular control of self-organization of hybrids

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials. Molecularly controlled mechanisms of biomineralization and application of the processes towards future material synthesis are introduced.

Ab initio and metadynamics studies on the role of essential functional groups in biomineralization of calcium carbonate and environmental situations

The interactions of proteins, polysaccharides and other biomolecules with Ca(2+), CO3(2-), and water are central to the understanding of biomineralization and crystallization of calcium carbonate (CaCO3), and their association with the natural organic matter (NOM) in the environment. A molecular-level investigation of how such interactions and thermodynamic forces drive the nucleation and growth of crystalline CaCO3 in living organisms remains elusive. This paper presents ab initio and metadynamics studies of the interactions of Ca(2+), CO3(2-), and water with the essential amino acids/functional groups, e.g. arginine/NH2(+), aspartate or glutamate/COO(-), aspartic or glutamic acid/COOH, and serine/OH, of protein/organic molecules that are likely to be critical to the biomineralization of CaCO3. These functional groups were modeled as guanidinium (Gdm(+)), acetate (AcO(-)), acetic acid (AcOH), and ethanol (EtOH) molecules, respectively. The Gdm(+)-Ca(2+)-CO3(2-) and AcO(-)-Ca(2+)-CO3(2-) systems were found to form stable ion-complexes irrespective of the presence of near neighbor water molecules. The strong electrostatic interactions of these functional groups with their counter-ions significantly affect the fundamental vibrational frequencies of the functional groups, mainly the NH2 stretching (str.) and degenerate (deg.) scissors modes of Gdm(+) and -C=OO, CC, and CO str. modes of AcO(-). The free-energy calculations reveal that EtOH forms weakly bound molecular complexes with the Ca(2+)-CO3(2-) ion pairs in water. However, the interaction strength of EtOH with crystalline CaCO3 can increase significantly due to combined effect of H-bond and electron donor acceptor (EDA) type of interactions. These results indicate that -NH2(+) and -COO(-) bearing molecules serve as potential nucleation sites promoting crystallization of CaCO3 phases while -OH bearing molecules are likely to control the morphology of the crystalline phases by attaching to the growing crystal surfaces.