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Mineralization is a ubiquitous process in the animal kingdom and is fundamental to human development and health. Dysfunctional or aberrant mineralization leads to a variety of medical problems, and so an understanding of these processes is essential to their mitigation. Osteoblasts create the nano-composite structure of bone by secreting a collagenous extracellular matrix (ECM) on which apatite crystals subsequently form. However, despite their requisite function in building bone and decades of observations describing intracellular calcium phosphate, the precise role osteoblasts play in mediating bone apatite formation remains largely unknown. To better understand the relationship between intracellular and extracellular mineralization, we combined a sample-preparation method that simultaneously preserved mineral, ions, and ECM with nano-analytical electron microscopy techniques to examine osteoblasts in an in vitro model of bone formation. We identified calcium phosphate both within osteoblast mitochondrial granules and intracellular vesicles that transported material to the ECM. Moreover, we observed calcium-containing vesicles conjoining mitochondria, which also contained calcium, suggesting a storage and transport mechanism. Our observations further highlight the important relationship between intracellular calcium phosphate in osteoblasts and their role in mineralizing the ECM. These observations may have important implications in deciphering both how normal bone forms and in understanding pathological mineralization.

Nanocrystals of apatitic calcium phosphate impart the organic-inorganic nanocomposite in bone with favorable mechanical properties. So far, the factors preventing crystal growth beyond the favorable thickness of ca. 3 nm have not been identified. Here we show that the apatite surfaces are studded with strongly bound citrate molecules, whose signals have been identified unambiguously by multinuclear magnetic resonance (NMR) analysis. NMR reveals that bound citrate accounts for 5.5 wt% of the organic matter in bone and covers apatite at a density of about 1 molecule per (2 nm)², with its three carboxylate groups at distances of 0.3 to 0.45 nm from the apatite surface. Bound citrate is highly conserved, being found in fish, avian, and mammalian bone, which indicates its critical role in interfering with crystal thickening and stabilizing the apatite nanocrystals in bone.

Background Root caries is preventable and can be arrested at any stage of disease development. The aim of this study was to investigate the potential mineral exchange and fluorapatite formation within artificial root carious lesions (ARCLs) using different toothpastes containing 5,000 ppm F, 1,450 ppm F or bioactive glass (BG) with 540 ppm F. Materials and methods The crowns of each extracted sound tooth were removed. The remaining roots were divided into four parts ( n  = 12). Each sample was randomly allocated into one of four groups: Group 1 (Deionised water); Group 2 (BG with 540 ppm F); Group 3 (1,450 ppm F) and Group 4 (5,000 ppm F). ARCLs were developed using demineralisation solution (pH 4.8). The samples were then pH-cycled in 13 days using demineralisation solution (6 h) and remineralisation solution (pH 7) (16 h). Standard tooth brushing was carried out twice a day with the assigned toothpaste. X-ray Microtomography (XMT) was performed for each sample at baseline, following ARCL formation and after 13-day pH-cycling. Scanning Electron Microscope (SEM) and 19 F Magic angle spinning nuclear magnetic resonance ( 19 F-MAS-NMR) were also performed. Results XMT results showed that the highest mineral content increase (mean ± SD) was Group 4 (0.09 ± 0.05), whilst the mineral content decreased in Group 1 (-0.08 ± 0.06) after 13-day pH-cycling, however there was evidence of mineral loss within the subsurface for Groups 1, 3 and 4 ( p  < 0.05). SEM scans showed that mineral contents within the surface of dentine tubules were high in comparison to the subsurface in all toothpaste groups. There was evidence of dentine tubules being either partially or completely occluded in toothpaste groups. 19 F-MAS-NMR showed peaks between − 103 and − 104ppm corresponding to fluorapatite formation in Groups 3 and 4. Conclusion Within the limitation of this laboratory-based study, all toothpastes were potentially effective to increase the mineral density of artificial root caries on the surface, however there was evidence of mineral loss within the subsurface for Groups 1, 3 and 4.

We present a new approach to determine in situ CO2 and H2O concentrations in apatite via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Absolute carbon and hydrogen measurements by nuclear reaction analysis (NRA) and elastic recoil detection (ERD) are used to calibrate ATR-FTIR spectra of CO2 and H2O in apatite. We show that CO2 and H2O contents in apatite can be determined via linear equations (r2 > 0.99) using the integrated area of CO2 and H2O IR absorption bands. The main benefits of this new approach are that ATR-FTIR analyses are non-destructive and can be conducted on polished sample material surfaces with a spatial resolution of ~ 35 μm. Furthermore, the wavenumber of the phosphate IR absorption band can be used to determine the crystallographic orientation of apatite, which allows for accurate quantification of CO2 and H2O in randomly orientated apatite grains. The limit of quantification of H2O in apatite is ~ 400 ppm and ~ 100 ppm for CO2. Via two examples, one from a carbonatite and one from a metasedimentary rock, we show that this new technique opens up new possibilities for determining volatile concentrations and behavior in a wide range of hydrothermal, igneous, and metamorphic systems.

The surface-directed mineralization of calcium phosphate from simulated body fluid is studied by cryogenic transmission electron microscopy. Prenucleation clusters aggregate close to the surface, then amorphous calcium phosphate forms in this region, leading to the nucleation of oriented apatite crystals at the surface. Unravelling the processes of calcium phosphate formation 1 , 2 , 3 , 4 is important in our understanding of both bone and tooth formation 5 , 6 , 7 , and also of pathological mineralization, for example in cardiovascular disease 8 , 9 , 10 . Serum is a metastable solution from which calcium phosphate precipitates in the presence of calcifiable templates such as collagen, elastin and cell debris 11 , 12 . A pathological deficiency of inhibitors leads to the uncontrolled deposition of calcium phosphate. In bone and teeth the formation of apatite crystals is preceded by an amorphous calcium phosphate (ACP) precursor phase 13 , 14 . ACP formation is thought to proceed through prenucleation clusters—stable clusters that are present in solution already before nucleation—as was recently demonstrated for CaCO 3 (refs  15 16 ). However, the role of such nanometre-sized clusters as building blocks 2 for ACP has been debated for many years. Here we demonstrate that the surface-induced formation of apatite from simulated body fluid 17 , 18 starts with the aggregation of prenucleation clusters leading to the nucleation of ACP before the development of oriented apatite crystals.

Autologous bone (AB) is the gold standard for bone-replacement surgeries 1 , despite its limited availability and the need for an extra surgical site. Traditionally, competitive biomaterials for bone repair have focused on mimicking the mineral aspect of bone, as evidenced by the widespread clinical use of bioactive ceramics 2 . However, AB also exhibits hierarchical organic structures that might substantially affect bone regeneration. Here, using a range of cell-free biomimetic-collagen-based materials in murine and ovine bone-defect models, we demonstrate that a hierarchical hybrid microstructure—specifically, the twisted plywood pattern of collagen and its association with poorly crystallized bioapatite—favourably influences bone regeneration. Our study shows that the most structurally biomimetic material has the potential to stimulate bone growth, highlighting the pivotal role of physicochemical properties in supporting bone formation and offering promising prospects as a competitive bone-graft material. By examining several cell-free biomimetic-collagen-based materials in murine and ovine bone-defect models, the twisted plywood pattern of collagen-based materials is shown to favourably influence bone regeneration and contributes to bone autograft performance.

As the hardest tissue formed by vertebrates, enamel represents nature’s engineering masterpiece with complex organizations of fibrous apatite crystals at the nanometer scale. Supramolecular assemblies of enamel matrix proteins (EMPs) play a key role as the structural scaffolds for regulating mineral morphology during enamel development. However, to achieve maximum tissue hardness, most organic content in enamel is digested and removed at the maturation stage, and thus knowledge of a structural protein template that could guide enamel mineralization is limited at this date. Herein, by examining a gene-modified mouse that lacked enzymatic degradation of EMPs, we demonstrate the presence of protein nanoribbons as the structural scaffolds in developing enamel matrix. Using in vitro mineralization assays we showed that both recombinant and enamel-tissue–based amelogenin nanoribbons are capable of guiding fibrous apatite nanocrystal formation. In accordance with our understanding of the natural process of enamel formation, templated crystal growth was achieved by interaction of amelogenin scaffolds with acidic macromolecules that facilitate the formation of an amorphous calcium phosphate precursor which gradually transforms into oriented apatite fibers along the protein nanoribbons. Furthermore, this study elucidated that matrix metalloproteinase-20 is a critical regulator of the enamel mineralization as only a recombinant analog of a MMP20-cleavage product of amelogenin was capable of guiding apatite mineralization. This study highlights that supramolecular assembly of the scaffold protein, its enzymatic processing, and its ability to interact with acidic carrier proteins are critical steps for proper enamel development.

This study investigated the effect of the application of apatite (Ap), some amendments (zeolite and molasses), and some microbial inoculations (plant-growth-promoting microorganisms; including Claroideoglomus etunicatum, Serendipita indica, Enterobacter cloacae, and Brevundimonas sp) on P in organic (Po) and P in inorganic (Pi) fractions, alkaline phosphatase activity, and Sorghum bicolor L. (Speedfed cultivar) growth in sandy soil with pH 7.8. A factorial pot experiment in a completely randomized design was performed with three replications, using microbial inoculants (non-inoculated, Claroideoglomus etunicatum, Serendipita indica, Enterobacter cloacae, and Brevundimonas sp) and four amendments levels (control, Ap, Ap-Z (Ap-zeolite), and Ap-M (Ap-molasses)). Ap application increased all mineral fractions of P as follows: Ca10-P > Ca8-P > Ca2-P > Olsen P. Application of Ap-Z led to the increase of Olsen-P and Ca2-P to 1.21 and 1.67 fold as compared to Ap. Po was very low in soil, which was increased significantly with the application of amendments. In Ap-M treatments, the moderately labile Po and moderately non-labile Po increased significantly as compared to Ap treatments. Application of Ap-Z reduced pH more than Ap and Ap-M treatments. Furthermore, the largest amount of alkaline phosphatase was observed in Ap-M treatments. These findings show various mechanisms of microorganisms for using Ap in their metabolism in the presence of different amendments. Microbial inoculation (especially C. etunicatum) resulted in a decrease in pH and an increase in alkaline phosphatase. Application of amendments (Ap-Z and then Ap-M) resulted in better growth of Sorghum compared to control and Ap treatments. Application of Ap with zeolite and then molasses along with inoculation with plant-growth-promoting microorganisms were two useful solutions to improve the productivity of sandy soils.

Phosphostrontium carbonate hydroxyapatites having the general formula Sr sub(10)(PO sub(4)) sub(6 )(OH) sub((2-2x))(CO sub(3)) sub(x) were prepared by solid gas reaction at different temperatures in the range 0 less than or equal to x less than or equal to 1. Infrared spectroscopy investigation reveals a carbonate groups substituting hydroxyl ions. Intensity bands increasing with the carbonate amount introduced in the lattice, while the one corresponding to hydroxyl decreases until disappearance. The Rietveld refinement of the structural model using X-ray powder diffraction patterns is used to determine the substitution rate. It was quantified by the refinement of the occupancy sites affected by the substitution. The crystallographic study shows the evolution of the atomic coordinate in the apatite due to the carbonate incorporation. The variation of the main interatomic distances and the bond angles was also discussed.

Teleosauridae and Metriorhynchidae were thalattosuchian crocodylomorph clades that secondarily adapted to marine life and coexisted during the Middle to Late Jurassic. While teleosaurid diversity collapsed at the end of the Jurassic, most likely as a result of a global cooling of the oceans and associated marine regressions, metriorhynchid diversity was largely unaffected, although the fossil record of Thalattosuchia is poor in the Cretaceous. In order to investigate the possible differences in thermophysiologies between these two thalattosuchian lineages, we analysed stable oxygen isotope compositions (expressed as δ 18 O values) of tooth apatite from metriorhynchid and teleosaurid specimens. We then compared them with the δ 18 O values of coexisting endo-homeothermic ichthyosaurs and plesiosaurs, as well as ecto-poikilothermic chondrichthyans and osteichthyans. The distribution of δ 18 O values suggests that both teleosaurids and metriorhynchids had body temperatures intermediate between those of typical ecto-poikilothermic vertebrates and warm-blooded ichthyosaurs and plesiosaurs, metriorhynchids being slightly warmer than teleosaurids. We propose that metriorhynchids were able to raise their body temperature above that of the ambient environment by metabolic heat production, as endotherms do, but could not maintain a constant body temperature compared with fully homeothermic ichthyosaurs and plesiosaurs. Teleosaurids, on the other hand, may have raised their body temperature by mouth-gape basking, as modern crocodylians do, and benefited from the thermal inertia of their large body mass to maintain their body temperature above the ambient one. Endothermy in metriorhynchids might have been a by-product of their ecological adaptations to active pelagic hunting, and it probably allowed them to survive the global cooling of the Late Jurassic, thus explaining the selective extinction affecting Thalattosuchia at the Jurassic–Cretaceous boundary. This article is part of the theme issue ‘Vertebrate palaeophysiology'.