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Waste seashells from aquaculture are a massive source of biogenic calcium carbonate (bCC) that can be a potential substitute for ground calcium carbonate and precipitated calcium carbonate. These last materials find several applications in industry after a surface coating with hydrophobic molecules, with stearate as the most used. Here, we investigate for the first time the capability of aqueous stearate dispersions to coat bCC powders from seashells of market-relevant mollusc aquaculture species, namely the oyster Crassostrea gigas, the scallop Pecten jacobaeus, and the clam Chamelea gallina. The chemical-physical features of bCC were extensively characterized by different analytical techniques. The results of stearate adsorption experiments showed that the oyster shell powder, which is the bCC with a higher content of the organic matrix, showed the highest adsorption capability (about 23 wt % compared to 10 wt % of geogenic calcite). These results agree with the mechanism proposed in the literature in which stearate adsorption mainly involves the formation of calcium stearate micelles in the dispersion before the physical adsorption. The coated bCC from oyster shells was also tested as fillers in an ethylene vinyl acetate compound used for the preparation of shoe soles. The obtained compound showed better mechanical performance than the one prepared using ground calcium. In conclusion, we can state that bCC can replace ground and precipitated calcium carbonate and has a higher stearate adsorbing capability. Moreover, they represent an environmentally friendly and sustainable source of calcium carbonate that organisms produce by high biological control over composition, polymorphism, and crystal texture. These features can be exploited for applications in fields where calcium carbonate with selected features is required.

Nanocrystalline calcium carbonate (CaCO) and amorphous CaCO (ACC) are materials of increasing technological interest. Nowadays, they are mainly synthetically produced by wet reactions using CaCO reagents in the presence of stabilizers. However, it has recently been discovered that ACC can be produced by ball milling calcite. Calcite and/or aragonite are the mineral phases of mollusk shells, which are formed from ACC precursors. Here, we investigated the possibility to convert, on a potentially industrial scale, the biogenic CaCO (bCC) from waste mollusk seashells into nanocrystalline CaCO and ACC. Waste seashells from the aquaculture species, namely oysters (Crassostrea gigas, low-Mg calcite), scallops (Pecten jacobaeus, medium-Mg calcite), and clams (Chamelea gallina, aragonite) were used. The ball milling process was carried out by using different dispersing solvents and potential ACC stabilizers. Structural, morphological, and spectroscopic characterization techniques were used. The results showed that the mechanochemical process produced a reduction of the crystalline domain sizes and formation of ACC domains, which coexisted in microsized aggregates. Interestingly, bCC behaved differently from the geogenic CaCO (gCC), and upon long milling times (24 h), the ACC reconverted into crystalline phases. The aging in diverse environments of mechanochemically treated bCC produced a mixture of calcite and aragonite in a species-specific mass ratio, while the ACC from gCC converted only into calcite. In conclusion, this research showed that bCC can produce nanocrystalline CaCO and ACC composites or mixtures having species-specific features. These materials can enlarge the already wide fields of applications of CaCO, which span from medical to material science.

Oyster shell wastes from the fishing industry represent a major environmental problem, as 7 million Tm/year are produced with no efficient recycling [1]. They are composed of Mgcalcite embedded in an organic matrix formed of proteins and polysaccharides. On the other hand, nanocrystalline apatites (NAp), which are structural and compositional analogues to the major inorganic component of human bones, exhibit excellent bioactivity and biocompatibility, and present a broad range of applications in hard tissue engineering, biomedicine, drug-delivery system and even in analytical sciences [2]. In this work, biogenic calcite from oyster shells was used to obtain apatite NPs by a ¿one-pot¿ hydrothermal process. Eu3+ and Tb3+ ions were added to the formulation to obtain Eu3+- and Tb3+-doped apatite NPs with luminescent properties. Solid-state characterization of the nanoparticles was performed by powder X-ray diffraction (PXRD), FT-IR and Raman spectroscopy, SEM and TEM microscopy, dynamic light scattering (DLS) and inductively coupled plasma (ICP) spectrometry, while luminescence properties were evaluated by luminescent spectroscopy. Finally, the biological behaviour of the NPs was evaluated by cytotoxicity and osteogenic differentiation assays, in murine mesenchymal (M17.1) and murine endothelial (MS-1) cells. Results demonstrated the efficiency of this novel ¿one pot¿ hydrothermal process to obtain nanoparticles of apatite with improved luminescent properties, while, in vitro assays demonstrated the excellent cytocompatibility and the impact of the metal-doping over the osteogenic differentiation capacity of the nanoparticles. Acknowledgment: This work was supported by project PCI2020-112108 funded by MCI/AEI/10.13039/501100011033 (Spain) and the European Union ¿NextGenerationEU¿/PRTR¿. PCI2020-112108 is part of the CASEAWA project of the ERA-NET Cofund BlueBio Programme, supported by the European Union (H2020).

Seashell wastes from aquaculture and canning industries represent an important environmental issue nowadays [1]. Shells are made of calcium carbonate (CaCO3) with a low content of proteins and polysaccharides (1-5 wt.%). The valorization of this waste by using it as a raw material for the production of calcium phosphates may have a positive impact both environmental and economic, thus contributing to the sustainability of this important sector. In some biomedical industries, there is a growing demand for calcium phosphate (apatite) crystals including nanosized, micron-sized, and larger sizes. This work is devoted to producing functional apatite nanocrystals, eg. doped with luminescent lanthanide (Ln3+) ions [2,3], using oyster shells (Mg-calcite, 5 wt.% Mg) from the species Crassostrea gigas as a Ca source. Experiments were performed by a one-pot hydrothermal method using KH2PO4 as a P reagent, a P/CaCO3 ratio of 0.6 (stoichiometric respect to hydroxyapatite), and either Eu3+ or Tb3+ (10and 20 mM). Characterization by XRD, FTIR, Raman, and ICP revealed the full transformation of biogenic CaCO3 particles into doped apatite. It was obtained at 160 ºC with (Ca+Ln)/P ratios 1.72 and 1.68 when adding Eu3+ and Tb3+ (10 mM) and 1.88 and 1.99 when the lanthanide concentration in the solution increased to 20 mM. In both cases, nanocrystals displayed needleor plate-like morphologies and polydisperse size distribution. Luminescence characterization of the nanoparticles showed different luminescence spectra depending on the doping ion. They displayed excitation and emission wavelengths of 395nm and 616 nm for the Eu3+-, and 372 and 543 nm for the Tb3+-doped samples. The relative luminescence intensities correlated well with their Ln3+ content while luminescence lifetimes (up to 1600 ¿s) were higher for Tb3+-doped apatites. Overall, the nanoparticles showed notable luminescent behavior and could find application as luminescent probes for bioimaging or nanophosphors for the elect

Fishery industry waste seashells represent an important environmental issue and imply the loss of potentially useful biomaterials [1]. They are composite materials made of CaCO3 and an organic matrix (1-5 wt.%) formed mainly of proteins and polysaccharides. Fabrication of functional calcium phosphates (eg. doped nanoapatites) using this type of biogenic CaCO3 as a calcium source may partially alleviate the ecological problem and be an alternative source of biocompatible materials intended for biomedical uses. In this work, the one-pot hydrothermal method [2] has been used in the preparation of biocompatible Mg2+, Mn2+, and Co2+-doped apatites. These divalent transition metal ions fulfill different roles in skeletal metabolism and may stimulate bone tissue regeneration [3-5]. The experiments were performed in a hydrothermal multitube set-up as well as in an autoclave, using oyster shell calcium carbonate particles from the species Crassostrea gigas, the KH2PO4 as a P reagent (P/CaCO3 0,6), and temperatures from 25ºC to 200ºC. Full transformation of CaCO3 was obtained at 160 ºC, yielding platy-shaped apatite nanoparticles doped with either 0.22 mol% Mg2+, 0.012 mol%Mn2+, or 0.16 mol% Co2+, and sizes within the range 75-90 nm. All samples showed a high cytocompatibility/biocompatibility when incubated with human mesenchymal stem cells for 1 and 3 days, and a small decrease in cell viability after 7 days of incubation in a dose-dependent concentration. Overall, the method was demonstrated to be promising in the preparation of doped biocompatible apatite nanocrystals with osteogenic features, and the biogenic CaCO3 a huge and unexplored calcium source for the preparation of apatite-based biomaterials. Acknowledgements: Grant ref. PCI2020-112108 is funded by MCIN/AEI/10.13039/501100011033 (Spain) and the European Union "NextGenerationEU"/PRTR". PCI2020-112108 is part of the project CASEAWA of ERA-NET Cofund BlueBio H2020.

Seashells are hierarchical bio-organic/mineral composites made of calcium carbonate (CaCO3) and an organic matrix (1-5 wt. %) composed mainly of proteins and polysaccharides. Fishery industry waste containing seashells from mussels, scallops, and oysters, represents an important environmental issue. The process is ecologically harmful and implies the loss of potentially useful biomaterials [1]. The valorization of seashell waste by transforming the CaCO3 crystals into biomimetic apatite micro/nanoparticles for biomedical applications may have a positive environmental impact besides economic profitability since the global market (including nano-sized, micron-sized, and higher sizes) is expected to grow in the next years. Different methods to transform biogenic CaCO3 into apatite nano/microparticles have been developed recently. They are mainly two-step processes involving calcination to CaO at 900-1000 °C followed by the reaction of a phosphate reagent (typically H3PO4) with the Ca(OH)2 produced by hydration of the CaO [2]. In this work, we have developed a one-step hydrothermal process to obtain biomimetic carbonated-apatite using oyster shells (Mg-calcite, 5 wt.% Mg) from the species Crassostrea gigas as model raw material. Shells were treated with NaClO 5% v/v to remove surface organic residues, crushed by a hammer mill, milled in a ball mill and sieved using a <45 ¿m mesh. The so obtained particles were submitted to hydrothermal treatment. Different experimental parameters were tested: P reagents (H3PO4, KH2PO4, and K2HPO4); P/Ca molar ratios (0.24, 0.6, and 0.96); temperature (25-200°C) and time (from 1 week to 2 months), without any pH adjustment. Characterization was performed by XRD, FTIR, Raman, SEM, TEM, DLS and TGA. The apatite/calcite ratio (wt.%) of the final precipitates was determined by Rietveld analysis using TOPAS 6.0 software. Among the many results, it is worth of mentioning that at the lowest experimental time used (1 week), the temperatures to o

Waste seashells from the fishery industry represent an important environmental issue. Its valorization by transforming the CaCO3 into apatite micro/nanoparticles may have a positive environmental impact besides an economic profitability since the global apatite market is expected to grow at 6.5% to around USD 3.086,05 million by 2027. Many of methods to transform biogenic CaCO3 into apatite particles are two-step processes involving calcination to CaO at 900-1000 °C followed by titration with a phosphate reagent (typically H3PO4). Here we present a one-step hydrothermal method using oyster shells Crassostrea gigas as model raw material. Shells were treated with NaClO 5% v/v, crushed, milled, and sieved (Ø<45 ¿m mesh), before submitting to hydrothermal conversion. Firstly, we explored the influences of KH2PO4 and K2HPO4, P/Ca molar ratios (0.24, 0.6, and 0.96), and temperature (25-200°C) in the transformation process. The minimum temperatures to obtain full transformation when using KH2PO4 and K2HPO4 for P/Ca molar ratios 0.6 (stoichiometric) were 160 ºC and 120ºC respectively, while for P/Ca ratios 0.96, they were 120 ºC and 80 ºC. The precipitates (Mg2+-doped carbonated-apatite micro/nanoparticles) are the result of a dissolution/re-precipitation mechanism driven by pH variation. Secondly, we explored the influence of osteogenic ions Mg2+, Mn2+, and Co2+ at P/Ca molar ratios 0.6. Full transformation of CaCO3 was obtained at 160 ºC, yielding platy-shaped apatite nanoparticles doped with either 0.22 mol% Mg2+, 0.012 mol% Mn2+, or 0.16 mol% Co2+, and sizes within the range 75-90 nm. Compared to the previous two-step processes, the one reported here is straightforward, one-pot, easily to scale up, and can be operated at relatively low temperatures without any pH adjustment.

Waste seashells from the fishery industry represent an important environmental issue and, at the same time, a loss of potentially useful biomaterials [1]. They are biominerals made of CaCO3 and an organic matrix (1-5 wt.%) composed mainly of proteins and polysaccharides. The fabrication of functional calcium phosphates such as doped nanoapatites, using seashells as a calcium source, could partially alleviate the ecological problem associated with this type of waste [2]. In this work, the one-pot hydrothermal method [2] has been used to obtain biocompatible Mg2+-, Mn2+-, and Co2+-doped apatites since these metals have been shown to stimulate bone tissue regeneration [3-5]. The experiments were performed by heating aqueous suspensions composed of oyster shell CaCO3 particles (490 mM) plus 300 mM KH2PO4, in presence of 10 mM of metal (M= Mg2+, Mn2+, or Co2+), at temperatures ranging from 25 ¿C to 200 ¿C. Full transformation of CaCO3 particles was achieved at 160 ¿C, resulting in M-doped, platy-shaped apatite nanoparticles, and sizes within the range of 75-90 nm. When incubated with human mesenchymal stem cells for 1 and 3 days, all samples showed high cytocompatibility/biocompatibility, with only a small decrease in cell viability after 7 days of incubation at dose-dependent concentrations. Overall, this method shows promise in the preparation of biocompatible doped-apatite nanocrystals with osteogenic features, utilizing biogenic CaCO3 as an unexplored calcium source for the preparation of apatite-based biomaterials. Acknowledgements: Grant ref. PCI2020-112108 is funded by MCIN/AEI/10.13039 /501100011033 (Spain) and the European Union ¿NextGenerationEU¿/PRTR¿. PCI2020-112108 is the Spanish part of the project CASEAWA of ERA-NET Cofund BlueBio H2020.

Biominerals are inorganic/organic hybrid solids formed by organisms. In mollusk shells calcium carbonate is the main component, where it represents more than 95 wt.%. These biominerals are characterized by a shape, morphology, and composition that differentiate them from their geogenic and synthetic counterparts [1]. Mollusk shells are a waste by-product from aquaculture whose disposal represents an environmental and economic issue but they also are a renewable and cheap alternative source for biogenic calcium carbonate [2]. In this context, the presented research regards the valorization of waste mussel shells from the species Mytilus galloprovincialis in order to recover biomineral building units using a simple, sustainable, and environmentally friendly procedure [3]. Mussel shell consists of three crystalline layers (Fig. 1A): the inner layer of aragonite nacre, the outer layer of calcite fibrous prisms and the myostracum [4]. In order to separate the different layers, different treatments have been applied. They were: a bleaching process with NaClO solution to remove the outer organic periostracum layer; a thermal treatment for the mechanical separation of nacre; an acidic treatment with a CH3COOH solution to remove the myostracum. The nacre layer was then separated into almost single aragonite tablets by a bleaching and sonication process (Fig. 1B) while the prismatic layer was crashed by mortar and pestle, sieved at 600 ¿m and treated with NaClO solution to obtain single fibrous crystals of calcite (Fig. 1C). The disassembled calcite fibers were stirred in water to form spherical aegagropilae-like aggregates of fibers (Fig. 1D) having a potential application for gas adsorption.

True control over the morphology of gypsum crystals formed via homogeneous precipitation from solution has rarely been reported in the literature. In this work, we have tested a large number of dissolved additives (polymers as well as small molecules) with respect to their ability to alter the typical microscopic appearance of precipitated gypsum powders, which is usually characterized by a mixture of single-crystalline needles and twinned plates. Among the many additives studied, a copolymer of vinylpyrrolidone and acrylic acid (PVP-co-PAA) was identified as powerful growth modifier for gypsum already at low concentrations. In both slow titration and rapid mixing experiments, unconventional blocky crystals with tilted stacking edges as well as pseudo-hexagonal plates could be synthesized reproducibly with the help of the copolymer. Systematic characterization revealed the dynamic mode of action of the newly identified growth modifier, which seems to stabilize a highly reactive face of gypsum and promote the formation of macrosteps. The degree of morphological control achieved in this way is unprecedented in the case of calcium sulfate and may devise entirely new concepts for additive design in the areas of plasters and cementitious materials, gypsum wallboard production and/or scale prevention.

The crystallization of calcium hydroxide (Ca(OH), CH, portlandite) is a key process during the early stages of cement hydration. In the present work, we have revisited the formation of this mineral through nucleation and growth from supersaturated aqueous solutions, in the light of the currently emerging picture of multistage “non-classical” crystallization. To that end, we developed a titration-based assay, in which stock solutions of both relevant ions are added simultaneously into a reservoir, where supersaturation increases slowly at constant stoichiometry until nucleation occurs. This procedure allows both pre- and early post-nucleation phenomena to be analyzed quantitatively. Complementarily, the early stages of portlandite mineralization were probed by various advanced characterization techniques, including cryo-transmission electron microscopy (cryo-TEM), in-situ small-angle X-ray scattering (SAXS), pair distribution function (PDF) analysis of high-energy X-ray scattering (HEXS) data, and analytical ultracentrifugation (AUC). The experimental data show that the formation of calcium hydroxide starts with the association of ions into complexes and clusters, which subsequently coalesce to form amorphous nanoparticles – much like what has been observed in the case of calcium carbonate and other prominent minerals. Subsequently, these particles aggregate and build networks, which eventually transform into hexagonal Ca(OH) crystals. The presence of a soluble polycarboxylate – as a known inhibitor of portlandite crystallization – does not change the main characteristics of this multistep nucleation pathway, but it proved capable of significantly extending the lifetime of the amorphous intermediate phase and thus delaying the transition to the final crystalline phase. Our observations confirm the notion that “non-classical” crystallization is a much more common phenomenon than initially believed – and that, for minerals forming in aqueous environments, it may actual

Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing process. Light-induced techniques are particularly interesting for this approach as they offer tremendous accuracy in spatial resolution. However, in the field of calcium phosphates, light-induced crystallization has not been investigated so far. Here, proof of principle is established to successfully induce carbonate-hydroxyapatite precipitation by light irradiation. Phosphoric acid is released by a photolabile molecule exclusively after irradiation, combining with calcium ions to form a calcium phosphate in the crystallization medium. 4-Nitrophenylphosphate (4NPP) is established as the photolabile molecule and the system is optimized and fully characterized. A calcium phosphate is crystallized exclusively by irradiation in aqueous solution and identified as carbonate apatite. Control over the localization and stabilization of the carbonate apatite is achieved by a pulsed laser, triggering precipitation in calcium and 4NPP-containing gel matrices. The results of this communication open up a wide range of new opportunities, both in the field of chemistry for more sophisticated reaction control in localized crystallization processes and in the field of medicine for enhanced treatment of calcium phosphate containing biomaterials.

We have developed a straightforward, one-pot, low-temperature hydrothermal method to transform oyster shell waste particles (bCCP) from the species Crassostrea gigas (Mg-calcite, 5 wt% Mg) into hydroxyapatite (HA) micro/nanoparticles. The influence of the P reagents (HPO, KHPO, and KHPO), P/bCCP molar ratios (0.24, 0.6, and 0.96), digestion temperatures (25-200 °C), and digestion times (1 week-2 months) on the transformation process was thoroughly investigated. At 1 week, the minimum temperature to yield the full transformation significantly reduced from 160 °C to 120 °C when using KHPO instead of KHPO at a P/bCCP ratio of 0.6, and even to 80 °C at a P/bCCP ratio of 0.96. The transformation took place via a dissolution-reprecipitation mechanism driven by the favorable balance between HA precipitation and bCCP dissolution, due to the lower solubility product of HA than that of calcite at any of the tested temperatures. Both the bCCP and the derived HA particles were cytocompatible for MG-63 human osteosarcoma cells and m17.ASC murine mesenchymal stem cells, and additionally, they promoted the osteogenic differentiation of m17.ASC, especially the HA particles. Because of their physicochemical features and biological compatibility, both particles could be useful osteoinductive platforms for translational applications in bone tissue engineering.

In this review article, selected, latest theoretical, and experimental developments in the field of nucleation and crystal growth of inorganic materials from aqueous solution are highlighted, with a focus on literature after 2015 and on non-classical pathways. A key point is to emphasize the so far underappreciated role of water and solvent entropy in crystallization at all stages from solution speciation through to the final crystal. While drawing on examples from current inorganic materials where non-classical behavior has been proposed, the potential of these approaches to be adapted to a wide-range of systems is also discussed, while considering the broader implications of the current re-assessment of pathways for crystallization. Various techniques that are suitable for the exploration of crystallization pathways in aqueous solution, from nucleation to crystal growth are summarized, and a flow chart for the assignment of specific theories based on experimental observations is proposed.

Formation of superstructures from colloidal dispersion involves a continuous increase in particle concentration, resulting in increasingly more complicated interparticle interaction. At high particle concentration, the presence of the super-crowding effect, strong non-ideality in addition to significant light absorption and scattering makes particle analysis very difficult. Here we report quantitative molecular, microscopic and macroscopic experimental results on like-charged colloids with concentration up to 60 vol%, close to the densest possible packing of spheres. It is achieved by conducting sedimentation-diffusion-equilibrium analytical ultracentrifugation (SE-AUC) on a concentrated dispersion of colloidal silica nanoparticles in a refractive-index-matching solvent. Surprisingly, we observed the self-association and even colloidal gel formation of like-charged colloids at very high concentration. Further experiments indicate that the attraction force may be counter-ion mediated. These results represent an important step forward in understanding complicated interparticle interaction in extremely high concentration, which is vital for the controlled fabrication of colloidal superstructures.

Control over the shape and morphology of single crystals is a theme of great interest in fundamental science and for technological application. Many synthetic strategies to achieve this goal are inspired by biomineralization processes. Indeed, organisms are able to produce crystals with high fidelity in shape and morphology utilizing macromolecules that act as modifiers. An alternative strategy can be the recovery of crystals from biomineralization products, in this case, seashells. In particular, waste mussel shells from aquaculture are considered. They are mainly built up of single crystals of calcite fibers and aragonite tablets forming an outer and an inner layer, respectively. A simple mechanochemical treatment has been developed to separate and recover these two typologies of single crystals. The characterization of these single crystals showed peculiar properties with respect to the calcium carbonate from quarry or synthesis. We exploited these biomaterials in the water remediation field using them as substrate adsorbing dyes. We found that these substrates show a high capability of adsorption for anionic dye, such as Eosin Y, but a low capability of adsorption for cationic dyes, such as Blue Methylene. The adsorption was reversible at pH 5.6. This application represents just an example of the potential use of these biogenic single crystals. We also envision potential applications as reinforcing fillers and optical devices.

Organic-inorganic composite materials with tailored properties can be designed in the lab through bio-inspired approaches. In this context, we exploited the particle-based crystallisation process of calcium sulfate, a technologically important mineral, to hybridise inorganic and organic matter. We identified and synthesised an organic polymer showing strong affinity to bind to the surfaces of mineral precursors as well as intrinsic tendency to self-organise. Subsequently, polymer-coated building units were allowed to self-assemble via oriented attachment, aggregation and phase transformation, which produced ordered superstructures where the organic polymer is intercalated between the subunits and surrounds the hybrid core as a shell. This specific architecture across multiple length scales leads to unique mechanical properties, comparable to those of natural biominerals. Thus, our results devise a straightforward pathway to prepare organic-inorganic hybrid structures via bottom-up self-assembly processes innate to the crystallisation of the inorganic phase. This approach can likely be transferred to other inorganic minerals, affording next-generation materials for applications in the construction sector, biomedicine and beyond.

Nucleation is a unique process with broad relevance across a wide range of scientific disciplines and applications. While considerable progress in the understanding of the mechanisms underlying the nucleation of minerals from solution has been made for popular model systems such as calcium carbonate, corresponding detailed insights are still missing for other, less prominent minerals. Here, we present a potentiometric titration-based method that allows the early stages of the crystallisation of brucite, Mg(OH), to be monitored and quantified. Together with complementary characterisation provided by (cryogenic) transmission electron microscopy, the collected data shed novel light on the species occurring prior to, during, and after nucleation of brucite. In the second part of the work, the newly developed approach was applied to investigate the effects of added poly(acrylic acid) on the different stages of the crystallisation process. The polymer is found to stabilise brucite nanoplatelets and co-precipitate with the inorganic phase, yielding a composite material. The methodology established in this study can readily be used to screen other chemistries for their ability to prevent magnesium hydroxide scaling and/or afford brucite nanomaterials with tailored properties.