Bio-Inspired Fluorescent Calcium Sulfate for the Conservation of Gypsum Plasterwork

In this work, the potential of bio-inspired strategies for the synthesis of calcium sulfate (CaSO4·nH2O) materials for heritage conservation is explored. For this, a nonclassical multi-step crystallization mechanism to understand the effect of calcein- a fluorescent chelating agent with a high affinity for divalent cations- on the nucleation and growth of calcium sulfate phases is proposed. Moving from the nano- to the macro-scale, this strategy sets the basis for the design and production of fluorescent nano-bassanite (NB-C; CaSO4·0.5H2O), with application as a fully compatible consolidant for the conservation of historic plasterwork. Once applied to gypsum (CaSO4·2H2O) plaster specimens, cementation upon hydration of nano-bassanite results in a significant increase in mechanical strength, while intracrystalline occlusion of calcein in newly-formed gypsum cement improves its weathering resistance. Furthermore, under UV irradiation, the luminescence produced by calcein molecules occluded in gypsum crystals formed upon nano-bassanite hydration allows the easy identification of the newly deposited consolidant within the treated gypsum plaster without altering the substrate's appearance.

Ferroelastic Control of the Multicolor Emission from a Triply Doped Organic Crystal

Emission from crystalline organic solids is often quenched by nonemissive energy-transfer deexcitation processes. While dispersion of fluorophores in polymers or other hosts has been used to enhance the emission intensity, this strategy results in randomization of guest orientation and optical losses at grain boundaries. Here, we report the doping of inherently nonemissive single crystals of anilinium bromide with three fluorescent organic molecules. The doping process equips the crystal with emission characteristics that tune from blue to deep orange. The emission intensity can be reversibly modulated by ferroelastic twinning, which causes the material to function as a multiemissive force sensor. This approach opens up new pathways in the manipulation of emissive properties in organic crystals and may have substantial implications for optoelectronic devices and sensors.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Biomineralized Materials as Model Systems for Structural Composites: Intracrystalline Structural Features and Their Strengthening and Toughening Mechanisms

Biomineralized composites, which are usually composed of microscopic mineral building blocks organized in 3D intercrystalline organic matrices, have evolved unique structural designs to fulfill mechanical and other biological functionalities. While it has been well recognized that the intricate architectural designs of biomineralized composites contribute to their remarkable mechanical performance, the structural features within and corresponding mechanical properties of individual mineral building blocks are often less appreciated in the context of bio-inspired structural composites. The mineral building blocks in biomineralized composites exhibit a variety of salient intracrystalline structural features, such as, organic inclusions, inorganic impurities (or trace elements), crystalline features (e.g., amorphous phases, single crystals, splitting crystals, polycrystals, and nanograins), residual stress/strain, and twinning, which significantly modify the mechanical properties of biogenic minerals. In this review, recent progress in elucidating the intracrystalline structural features of three most common biomineral systems (calcite, aragonite, and hydroxyapatite) and their corresponding mechanical significance are discussed. Future research directions and corresponding challenges are proposed and discussed, such as the advanced structural characterizations and formation mechanisms of intracrystalline structures in biominerals, amorphous biominerals, and bio-inspired synthesis.

Patterned crystal growth and heat wave generation in hydrogels

The crystallization of metastable liquid phase change materials releases stored energy as latent heat upon nucleation and may therefore provide a triggerable means of activating downstream processes that respond to changes in temperature. In this work, we describe a strategy for controlling the fast, exothermic crystallization of sodium acetate from a metastable aqueous solution into trihydrate crystals within a polyacrylamide hydrogel whose polymerization state has been patterned using photomasks. A comprehensive experimental study of crystal shapes, crystal growth front velocities and evolving thermal profiles showed that rapid growth of long needle-like crystals through unpolymerized solutions produced peak temperatures of up to 45˚C, while slower-crystallizing polymerized solutions produced polycrystalline composites and peaked at 30˚C due to lower rates of heat release relative to dissipation in these regions. This temperature difference in the propagating heat waves, which we describe using a proposed analytical model, enables the use of this strategy to selectively activate thermoresponsive processes in predefined areas.

The crystallization of metastable liquid phase change materials releases stored energy upon nucleation. Here, the authors demonstrate area-selective activation of thermoresponsive processes by exothermic crystallization of sodium acetate into trihydrate crystals within a patterned polyacrylamide hydrogel.

In vitro crystallization of calcium carbonate mediated by proteins extracted from P. placenta shells

The ASM extracted from the shells of P. placenta can stabilize ACC and inhibit secondary nucleation for 10 hours, and an explosive secondary nucleation and quick crystal growth from 50 nm to 10 μm can be finished on the shell surface in one hour.

Prestressing Strategy for Strengthening Biocomposites: A Numerical Study

Natural materials developed in complex architectures that comprise hard and soft phases often display extraordinary mechanical properties, such as the combination of high strength and toughness. Besides the structural arrangements, residual stress is ubiquitous in those materials. Although evidence shows its significant role in the functionalities and properties of the composites, good or bad, residual stress is not fully understood and utilized. In this study, we show through extensive numerical simulations the role of the prestress in strengthening typical brick-and-mortar biocomposites. We investigate the influence of the prestressing modes, as well as the geometrical and material parameters. The results promise a deep understanding of the relation between the prestress and the material strength and may inspire a new dimension of material design.

Specifiable biomimetic microsponges for timed release of crystal entrapped biomolecules useful in bone repair

Most marine materials, by nature, contain crystals of inorganic matter with specific structures that allow the loading, release, and delivery of biomolecules that can be utilized in clinical applications. These structures can be biomimetically synthesized. Aggregates of inorganic particles generated by biomimetic microsponges may provide surfaces and structures for cell attachment, organization, and promotion of matrix synthesis. Biomimetic microsponges have been developed with tunable release profiles differing by the rate (speed over distance), velocity (rate of change in direction), and the quantity discharged over time, according to biomolecular species. Specifically, the types of proteins involved guide and regulate cells in physical contact with the microsponges, for instance, reprogramming somatic cells, the switching phenotypes, or specifying stem cell differentiation. Applications for these microsponges include gene transfection of localized cells and promotion of bone matrix synthesis by the externalized display of RGD cell adhesive peptides and the release of crystal entrapped, occluded, adsorbed and infused rhBMP-2 and plasmid. A requirement for de novo bone formation is a solid structure to enable osteocytes to lay new bone tissue. In this study, biomimetic microsponges highlight tremendous potential as osteoconductive packing material in bone repair with parallel influence on regeneration. Majorly, microsponges offer pronounced osteoinductivity, unlike many other bone particulates, by solid-state integration of active regenerative biological molecules through the prism of the biomineral crystalline structure.

Strategies for simultaneous strengthening and toughening via nanoscopic intracrystalline defects in a biogenic ceramic

While many organisms synthesize robust skeletal composites consisting of spatially discrete organic and mineral (ceramic) phases, the intrinsic mechanical properties of the mineral phases are poorly understood. Using the shell of the marine bivalve Atrina rigida as a model system, and through a combination of multiscale structural and mechanical characterization in conjunction with theoretical and computational modeling, we uncover the underlying mechanical roles of a ubiquitous structural motif in biogenic calcite, their nanoscopic intracrystalline defects. These nanoscopic defects not only suppress the soft yielding of pure calcite through the classical precipitation strengthening mechanism, but also enhance energy dissipation through controlled nano- and micro-fracture, where the defects' size, geometry, orientation, and distribution facilitate and guide crack initialization and propagation. These nano- and micro-scale cracks are further confined by larger scale intercrystalline organic interfaces, enabling further improved damage tolerance.

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.

Helical Microstructures of the Mineralized Coralline Red Algae Determine Their Mechanical Properties

Through controlled biomineralization, organisms yield complicated structures with specific functions. Here, Jania sp., an articulated coralline red alga that secretes high-Mg calcite as part of its skeleton, is in focus. It is shown that Jania sp. exhibits a remarkable structure, which is highly porous (with porosity as high as 64 vol%) and reveals several hierarchical orders from the nano to the macroscale. It is shown that the structure is helical, and proven that its helical configuration provides the alga with superior compliance that allows it to adapt to stresses in its natural environment. Thus, the combination of high porosity and a helical configuration result in a sophisticated, light-weight, compliant structure. It is anticipated that the findings on the advantages of such a structure are likely to be of value in the design or improvement of lightweight structures with superior mechanical properties.

Retinoic acid/calcite micro-carriers inserted in fibrin scaffolds modulate neuronal cell differentiation

The controlled release of cell differentiating agents is crucial in many aspects of regenerative medicine. Here we propose the use of hybrid calcite single crystals as micro-carriers for the controlled and localized release of retinoic acid, which is entrapped within the crystalline lattice. The release of retinoic acid occurs only in the proximity of stem cells, upon dissolution of the calcite hybrid crystals that are dispersed in the fibrin scaffold. These hybrid crystals provide a sustained dosage of the entrapped agent. The environment provided by this composite scaffold enables differentiation towards neuronal cells that form a three-dimensional neuronal network.

Bioinspired Materials: From Living Systems to New Concepts in Materials Chemistry

Nature successfully employs inorganic solid-state materials (i.e., biominerals) and hierarchical composites as sensing elements, weapons, tools, and shelters. Optimized over hundreds of millions of years under evolutionary pressure, these materials are exceptionally well adapted to the specifications of the functions that they perform. As such, they serve today as an extensive library of engineering solutions. Key to their design is the interplay between components across length scales. This hierarchical design-a hallmark of biogenic materials-creates emergent functionality not present in the individual constituents and, moreover, confers a distinctly increased functional density, i.e., less material is needed to provide the same performance. The latter aspect is of special importance today, as climate change drives the need for the sustainable and energy-efficient production of materials. Made from mundane materials, these bioceramics act as blueprints for new concepts in the synthesis and morphosynthesis of multifunctional hierarchical materials under mild conditions. In this review, which also may serve as an introductory guide for those entering this field, we demonstrate how the pursuit of studying biomineralization transforms and enlarges our view on solid-state material design and synthesis, and how bioinspiration may allow us to overcome both conceptual and technical boundaries.

In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization

Otoliths are one of the biominerals whose formation is highly controlled by proteins. The first protein discovered to be involved in otolith biomineralization in zebrafish was starmaker (Stm). Previously, Stm was shown to be responsible for the preferential formation of aragonite, a polymorph of calcium carbonate, in otoliths. In this work, proteomic analysis of adult zebrafish otoliths was performed. Stm is the only highly phosphorylated protein found in our studies. Besides previously studied otolith proteins, we discovered several dozens of unknown proteins that reveal the likely mechanism of biomineralization. A comparison of aragonite and vaterite otoliths showed similarities in protein composition. We observed the presence of Stm in both types of otoliths. In vitro studies of 2 characteristic Stm fragments indicated that the DS-rich region has a special biomineralization activity, especially after phosphorylation.-Kalka, M., Markiewicz, N., Ptak, M., Sone, E. D., Ożyhar, A., Dobryszycki, P., Wojtas, M. In vivo and in vitro analysis of starmaker activity in zebrafish otolith biomineralization.

Element banding and organic linings within chamber walls of two benthic foraminifera

Trace and minor elements incorporated in foraminiferal shells are among the most used proxies for reconstructing past environmental conditions. A prominent issue concerning these proxies is that the inter-specimen variability in element composition is often considerably larger than the variability associated with the environmental conditions for which the proxy is used. Within a shell of an individual specimen the trace and minor elements are distributed in the form of bands of higher and lower concentrations. It has been hypothesized that differences in specimen-specific element banding patterns cause the inter-specimen and inter-species variability observed in average element composition, thereby reducing the reliability of proxies. To test this hypothesis, we compared spatial distributions of Mg, Na, Sr, K, S, P and N within chamber walls of two benthic foraminiferal species (Amphistegina lessonii and Ammonia tepida) with largely different average Mg content. For both species the selected specimens were grown at different temperatures and salinities to additionally assess how these parameters influence the element concentrations within the shell wall. Our results show that Mg, Na, Sr and K are co-located within shells, and occur in bands that coincide with organic linings but extend further into the calcite lamella. Changes in temperature or salinity modulate the element-banding pattern as a whole, with peak and trough heights co-varying rather than independently affected by these two environmental parameters. This means that independent changes in peak or trough height do not explain differences in average El/Ca between specimens. These results are used to evaluate and synthesize models of underlying mechanisms responsible for trace and minor element partitioning during calcification in foraminifera.

Spatially Controlled Occlusion of Polymer-Stabilized Gold Nanoparticles within ZnO

In principle, incorporating nanoparticles into growing crystals offers an attractive and highly convenient route for the production of a wide range of novel nanocomposites. Herein we describe an efficient aqueous route that enables the spatially controlled occlusion of gold nanoparticles (AuNPs) within ZnO crystals at up to 20 % by mass. Depending on the precise synthesis protocol, these AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. Remarkably, such efficient occlusion is mediated by a non-ionic water-soluble polymer, poly(glycerol monomethacrylate)₇₀ (G₇₀ ), which is chemically grafted to the AuNPs; pendent cis-diol side groups on this steric stabilizer bind Zn²⁺ cations, which promotes nanoparticle interaction with the growing ZnO crystals. Finally, uniform occlusion of G₇₀ -AuNPs within this inorganic host leads to faster UV-induced photodegradation of a model dye.

A novel basic matrix protein of Pinctada fucata, PNU9, functions as inhibitor during crystallization of aragonite

The injection of dsRNA of PNU9 could lead to the overgrowth of nacreous lamellas and the matrix membrane.

Anionic block copolymer vesicles act as Trojan horses to enable efficient occlusion of guest species into host calcite crystals

We report a versatile 'Trojan Horse' strategy using highly anionic poly(methacrylic acid)-poly(benzyl methacrylate) vesicles to incorporate two types of model payloads, i.e. either silica nanoparticles or an organic dye (fluorescein), within CaCO3 (calcite). Uniform occlusion of silica-loaded vesicles was confirmed by scanning electron microscopy, while thermogravimetry studies indicated extents of vesicle occlusion of up to 9.4% by mass (∼33% by volume). Efficient dye-loaded vesicle occlusion produces highly fluorescent calcite crystals as judged by fluorescence microscopy. In control experiments, silica nanoparticles alone are barely occluded, while only very weakly fluorescent calcite crystals are obtained when using just the fluorescein dye. This new 'Trojan Horse' strategy opens up a generic route for the efficient occlusion of various nanoparticles and organic molecules within inorganic host crystals.

Residual Strain and Stress in Biocrystals

The development of residual strains within a material is a valuable engineering technique for increasing the material's strength and toughness. Residual strains occur naturally in some biominerals and are an important feature that is recently highlighted in biomineral studies. Here, manifestations of internal residual strains detected in biominerals are reviewed. The mechanisms by which they develop, as well as their impact on the biominerals' mechanical properties, are described. The question as to whether they can be utilized in multiscale strengthening and toughening strategies for biominerals is discussed.

The role of phosphorylation and dephosphorylation of shell matrix proteins in shell formation: an in vivo and in vitro study

Phosphorylation of shell matrix proteins is critical for shell formation in vivo and can modulate calcium carbonate formation in vitro.

Insights on the interaction of calcein with calcium carbonate and its implications in biomineralization studies

The effects of calcein, a fluorescent marker commonly used to assess mineral growth in calcifying organisms, on calcite and aragonite structure have been investigated.

Crystallization and structural properties of a family of isotopological 3D-networks: the case of a 4,4′-bipy ligand–M2+ triflate system

Desolvation process characterization of a flexible coordination network performed by time-resolved single-crystal X-ray diffraction. Influence of the metal centre on the network stability.

Biogenic and Synthetic Peptides with Oppositely Charged Amino Acids as Binding Sites for Mineralization

Proteins regulate diverse biological processes by the specific interaction with, e.g., nucleic acids, proteins and inorganic molecules. The generation of inorganic hybrid materials, such as shell formation in mollusks, is a protein-controlled mineralization process. Moreover, inorganic-binding peptides are attractive for the bioinspired mineralization of non-natural inorganic functional materials for technical applications. However, it is still challenging to identify mineral-binding peptide motifs from biological systems as well as for technical systems. Here, three complementary approaches were combined to analyze protein motifs consisting of alternating positively and negatively charged amino acids: (i) the screening of natural biomineralization proteins; (ii) the selection of inorganic-binding peptides derived from phage display; and (iii) the mineralization of tobacco mosaic virus (TMV)-based templates. A respective peptide motif displayed on the TMV surface had a major impact on the SiO₂ mineralization. In addition, similar motifs were found in zinc oxide- and zirconia-binding peptides indicating a general binding feature. The comparative analysis presented here raises new questions regarding whether or not there is a common design principle based on acidic and basic amino acids for peptides interacting with minerals.

Tuning hardness in calcite by incorporation of amino acids

Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unit-mineral single crystals containing embedded macromolecules-remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.

Structural analysis of metal-doped calcium oxalate

Calcium oxalate is a promising candidate towards the purification of environmental metal contaminants by adsorption and incorporation processes.