Growth, structure and mechanical properties of phosphate based bio-composites studied by ex situ and in situ Raman spectroscopy

This study contains the investigation of the formation of carbonate apatite (cAp) from a citrate-stabilized amorphous calcium phosphate (cit-ACP) phase in various ionic solutions. This is primarily realized via in situ Raman spectroscopy by studying the variation of the v1 phosphate stretching mode as a function of maturation time. The transition is complemented by ex situ transmission electron microscopy (TEM) for microstructural characterization. These observations shed light on the possible pathway regulating in vivo formation of cAp in bone. Further, the impact of titanium substitution on the electronic properties of apatite was assessed via structural characterization of titanium substituted hydroxyapatite (Ti/HA) composites performed by ex situ Raman spectroscopy and TEM. Raman studies revealed the formation and evolution of titanium oxide and calcium phosphate related phases, whereas TEM studies showed the morphological evolution of particles. Following cit-ACP transformation, the mechanical and molecular properties of collagen/cAp bio-inspired structures are studied by in situ Raman spectroscopy under mechanical stress. The impact of cAp content on the molecular response of these structures is highlighted by a wavenumber shift of collagen related Raman bands. This interplay between cAp and collagen is associated to the mechanical properties of bone

In situ mechanical and molecular investigations of collagen/apatite biomimetic composites combining Raman spectroscopy and stress-strain analysis

We report the design, fabrication and application of a novel micro-electromechanical device coupled to a confocal Raman microscope that enables in situ molecular investigations of micro-fibers under uniaxial tensile load. This device allows for the mechanical study of micro-fibers with diameters in the range between 10 and 100 lm and lengths of several hundred micrometers. By exerting forces in the mN range, the device enables an important force range to be accessed between that of atomic force microscopy and macroscopic stress-strain measurement devices. The load is varied using a stiffness-calibrated glass micro-needle driven by a piezo-translator during simultaneous Raman microscopy imaging. The method enables experiments probing the molecular response of micro-fibers to external stress. This set-up was applied to biomimetic non-mineralized and mineralized collagen micro-fibers revealing that above 30% mineralization the proline-related Raman band shows a pronounced response to stress, which is not observed in non-mineralized collagen. This molecular response coincides with a strong increase in the Young’s modulus from 0.5 to 6 GPa for 0% and 70% mineralized collagen, respectively. Our results are consistent with a progressive interlocking of the collagen triple-helices by apatite nanocrystals as the degree of mineralization increases

Misleading residues on lithics from Star Carr : identification with Raman microspectroscopy

Ancient trace residues left on stone artefacts by people represent a source of potentially fruitful data about diet, technology, and behaviour, but their investigation is not problem-free. Rather, correct identification of degraded residues and determination of their natural or anthropogenic origin remains at the heart of current methodological development in lithic residue analysis. It is increasingly becoming clear that reflected visible light microscopy (VLM) is insufficient to make secure identifications of ambiguous residues. Confocal Raman microspectroscopy (micro-Raman) is a non-destructive technique that can identify the specific molecular nature of microscopic residues with high spatial resolution. Here, the identification of artefact residues as anthropogenic by visual inspection alone was found to be incorrect in all cases tested. Micro-Raman provided the key source of information to unambiguously determine the chemical nature of residues and hence their origin

Crystallization of citrate-stabilized amorphous calcium phosphate to nanocrystalline apatite : a surface-mediated transformation

This work explores the mechanisms underlying the crystallization of citrate-functionalized amorphous calcium phosphate (cit-ACP) in two relevant media, combining in situand ex situ characterization techniques. Results demonstrate that citrate desorption from cit-ACP triggers the surface-mediated transformation to nanocrystalline apatite (Ap). Our findings shed light on the key role of citrate, an important component of bone organic matrix, and the medium composition in controlling the rate of transformation and the morphology of the resulting Ap phase

Biomineralization of a titanium-modified hydroxyapatite semiconductor on conductive wool fibers

Metal ions are frequently incorporated into crystalline materials to improve their electrochemical properties and to confer new physicochemical properties. Naturally-occurring phosphate apatite, which is formed geologically and in biomineralization processes, has extensive potential applications and is therefore an attractive functional material. In this study, we generate a novel building block for flexible optoelectronics using bio-inspired methods to deposit a layer of photoactive titanium-modified hydroxyapatite (TiHA) nanoparticles (NPs) on conductive polypyrrole(PPy)-coated wool yarns. The titanium concentration in the reaction solution was varied between 8-50 mol% with respect to the phosphorous, which led to titanate ions replacing phosphate in the hydroxyapatite lattice at levels up to 17 mol%. PPy was separately deposited on wool yarns by oxidative polymerization, using two dopants: (i) anthraquinone-2,6-disulfonic acid to increase the conductivity of the PPy layer and (ii) pyroglutamic acid, to reduce the resistivity of the wool yarns and to promote the heterogeneous nucleation of the TiHA NPs. A specific titanium concentration (25 mol% wrt P) was used to endow the TiHA NPs on the PPy-coated fibers with a desirable band gap value of 3.68 eV, and a specific surface area of 146 m2 g-1. This is the first time that a thin film of a wide-band gap semiconductor has been deposited on natural fibers to create a fiber-based building block that can be used to manufacture flexible electronic devices

Nucleation Pathway of Calcium Sulfate Hemihydrate (Bassanite) from Solution: Implications for Calcium Sulfates on Mars

International audienceCaSO4 minerals (i.e., gypsum, anhydrite, and bassanite) are widespread in natural and industrial environments. During the last several years, a number of studies have revealed that nucleation in the CaSO4–H2O system is nonclassical, where the formation of crystalline phases involves several steps. Based on these recent insights, we have formulated a tentative general model for calcium sulfate precipitation from solution. This model involves primary species that are formed through the assembly of multiple Ca2+ and SO42– ions into nanoclusters. These nanoclusters assemble into poorly ordered (i.e., amorphous) hydrated aggregates, which in turn undergo ordering into coherent crystalline units. The thermodynamic (meta)stability of any of the three CaSO4 phases is regulated by temperature, pressure, and ionic strength, with gypsum being the stable form at low temperatures and low-to-medium ionic strengths and anhydrite being the stable phase at high temperatures and at lower temperature for high salinities. Bassanite is metastable across the entire phase diagram but readily forms as the primary phase at high ionic strengths across a wide range of temperatures and can persist up to several months. Although the physicochemical conditions leading to bassanite formation in aqueous systems are relatively well established, nanoscale insights into the nucleation mechanisms and pathways are still lacking. To fill this gap and to further improve our general model for calcium sulfate precipitation, we conducted in situ scattering measurements at small-angle X-ray scattering and wide-angle X-ray scattering and complemented these with in situ Raman spectroscopic characterization. Based on these experiments, we show that the process of formation of bassanite from aqueous solutions is very similar to the formation of gypsum: it involves the aggregation of small primary species into larger disordered aggregates, only from which the crystalline phase develops. These data thus confirm our general model of CaSO4 nucleation and provide clues to explain the abundant occurrence of bassanite on the surface of Mars (and not on the surface of Earth)

A unique engraved shale pendant from the site of Star Carr: the oldest Mesolithic art in Britain

In 2015 an engraved shale pendant was found during excavations at the Early Mesolithic site of Star Carr, UK. Engraved motifs on Mesolithic pendants are extremely rare, with the exception of amber pendants from southern Scandinavia. The artwork on the pendant is the earliest known Mesolithic art in Britain; the 'barbed line' motif is comparable to styles on the Continent, particularly in Denmark. When it was first uncovered the lines were barely visible but using a range of digital imaging techniques it has been possible to examine them in detail and determine the style of engraving as well as the order in which the lines might have been made. In addition, microwear and residue analyses were applied to examine whether the pendant showed signs that it had been strung or worn, and whether the lines had been made more visible through the application of pigments, as has been suggested for some Danish amber pendants. This approach of using multiple scientific and analytical techniques has not been used previously and provides a methodology for the examination of similar artefacts in the future