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Abstract: The deposition of calcium phosphate mineral within a collagen matrix plays a pivotal role in the formation of bone and teeth, yet understanding its precise mechanism and time-dependence remains a significant challenge. Conventional approaches are often constrained to ex situ studies and as a result the intrinsic dynamics governing collagen mineralization remains unclear. To address this knowledge gap, we developed a custom thermal flow cell to enable in situ characterization using Raman spectroscopy and small/wide-angle X-ray scattering for comparable sample settings. This approach allowed us to monitor the intricate process of collagen matrix mineralization from the initial infiltration of precursor phases to the formation of intermediate phosphate phases, and ultimately to the predominant growth of hydroxyapatite. Our findings reveal a striking expansion of the collagen matrix during initial infiltration, followed by compression in the early stages of mineralization, likely driven by water expulsion, which suggests the development of pre-stress similar to that observed in bone. As mineralization progressed, the matrix expanded once again, correlated with crystal growth. Post-mortem analyses confirmed the presence of intrafibrillar mineralization, with remarkable agreement to bone formation at up to 9 h of mineralization before over-mineralization occurred. Our study further identified a tessellated mineralization pattern within the collagen matrix, a feature also seen in bone, pointing to a highly regulated physico-chemical control of the mineralization dynamics. These insights deepen our understanding of the fundamental processes governing bone mineralization with broad implications for designing advanced biomaterials.

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Abstract: Uranium dioxide (UO₂) particles can be released from mines, nuclear fuel manufacturing, reactor accidents, and weapons use. They pose inhalation risks, yet their behavior in the human lung remains poorly understood. This study investigates the long-term chemical alteration and dissolution of µm-sized UO₂ particles in two model lung fluids: Simulated Lung Fluid (SLF) and Artificial Lysosomal Fluid (ALF), representing extracellular and intracellular lung environments, respectively. Particles were exposed to each fluid at 37°C for up to 180 days (SLF) and 900 days (ALF). In SLF, UO₂ showed low apparent solubility (<2% U released to solution), but solid-phase analyses revealed significant oxidation of U(IV) (~50%) and formation of autunite-like sheets on the UO2 surface. Secondary phase formation may lessen overall UO2 dissolution, promoting long-term particle retention, whilst modifying particle chemical toxicity and cell uptake. In contrast, Monte Carlo simulations indicate that the SLF-induced surface alteration would reduce (>50%) external radiation dose from the particles. In contrast, UO₂ readily dissolved in ALF (~75% uranium released to solution in 60 days, ~100% by 900 days). There was no evidence of secondary phase formation in ALF, but extensive particle matrix dissolution/disaggregation was observed by 30 days. Fragmentation of the UO2 polycrystalline matrix may lead to release of smaller UO₂ crystallites, which could translocate more readily. Overall, this work provides new mechanistic insight into the fate of inhaled UO₂ under physiologically relevant conditions, highlighting a possible need to consider particle reactivity and alteration processes in health risk assessments.

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Abstract: In situ microscopy involves imaging of samples under real reaction conditions. For electron microscopy, micro-electromechanical systems (MEMS) chips have previously been developed that can hold a liquid or gas inside the vacuum of the electron microscope, with electrical contacts that allow for heating or biasing of the sample. These chips have paved the way for high-resolution imaging of dynamic chemical reactions. Here, we report the use of such MEMS chips in an in-house developed setup for a hard X-ray nanoprobe, applied to Ni-rich cathode materials. We investigate the chemical and structural changes in nickel-rich cathodes upon exposure to electrolyte and under heating conditions using hard X-ray spectromicroscopy. As such, we find marked differences in the behaviour of pure LiNiO2 compared to Co and Mn substituted material, NMC811. The use of hard X-ray spectromicroscopy allows for imaging and observation of: (i) the oxidation state of nickel, changing from Ni3+ to Ni2+, (ii) the effect of a preexisting fracture in the sample and (iii) the structural degradation of the sample during accelerated aging.

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Abstract: One of the key parameters defining the healthy functioning of soil is its structure. The organization of mineral particles, organic matter (OM), water, and air into a complex matrix of soil aggregates plays a particularly important role in long-term carbon (C) storage, as C compounds can be ‘hidden’ within the aggregate structure, shielding them from decomposers. Soil aggregation is a dynamic process influenced by physical, chemical, and biological factors; however, the individual and combined effects of these factors on the formation and turnover of aggregates are not well understood. The aim of this study was to examine the incorporation of fresh litter inputs with differing physicochemical properties, including their carbon-to-nitrogen (C/N) ratio—maize (C/N = 12) and straw (C/N = 103)—into aggregates formed de novo from mineral soil, with or without the presence of microbiota. Using rare-earth element oxides, we labeled structures formed during a four-week incubation with a single litter type and traced their incorporation into newly formed aggregates after mixing the soils and incubating them for a subsequent seven-week period. We found that, regardless of quality, litter was the most important factor driving soil aggregation during the initial stages of the process. The presence of both litter types together further enhanced aggregate formation. Contrary to our hypothesis, and likely due to the short time frame of the experiment, neither microbial abundance nor community composition significantly affected overall aggregation. However, further visualization of the different litter-associated structures across the cross-sections of the aggregates from various size fractions using synchrotron radiation-based X-ray fluorescence nanospectroscopy (SR-nanoXRF) enabled us to estimate potential influence of the microbes via their preferred litter type. Specifically, contrary to our expectations the bulk analysis showed that bacteria-favoured low C/N ratio maize litter had a stronger effect on both overall aggregation and the formation of macroaggregates, which we initially hypothesized would be supported by the high C/N ratio straw litter preferred by fungi. However, further analysis of the XRF intensity maps confirmed an increasing incorporation of straw-associated soils into >250 μm structures, likely facilitated by fungal growth and hyphal enmeshing. Phospholipid fatty acid analysis further corroborated this, showing a relatively higher abundance of fungi in macroaggregates in straw-containing soil. We also implemented semi-variogram analysis on the XRF maps, which allowed us to estimate the size and distribution of straw- and maize-associated structures within the aggregates. We found that while microaggregates were more commonly formed from individual litter-associated structures, larger aggregates (> 250 μm) were newly made from de-aggregated soil. In conclusion, our study provides insights into the initial stages of aggregate formation following litter additions and the development of associated microbial communities. The spatial analysis enabled by SR-nanoXRF allowed us to visualize internal aggregate structures, shedding light on processes that cannot be fully understood through bulk analysis alone.

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Abstract: Soil aggregation is a dynamic process influenced by physical, chemical and biological factors; however, their individual and combined effect on the formation and turnover of aggregates is not well understood. The aim of this study was to examine incorporation of fresh litter inputs of different physicochemical properties including their carbon-to-nitrogen (C/N) ratio – maize (C/N = 12) and straw (C/N = 103) - into aggregates, de novo formed from mineral soil with or without the presence of microbiota. Using rare-earth element oxides, we labelled structures formed during a four-week incubation with a single litter type and traced their incorporation into newly formed aggregates after mixing them together and incubating for a subsequent seven-week period. To visualize them, we used synchrotron-based X-ray fluorescence microspectroscopy, which allowed us to demonstrate that presence of the plant-derived particulate organic matter was the key factor for the aggregate formation. Within the timescale of the experiment, neither microbial abundance nor the community composition had any significant effect. However, the relative increase in straw-associated soil in aggregates larger than 250 μm provided support for our hypothesis regarding impact of carbon-rich organic matter on macroaggregation, likely via promotion of fungal growth and hyphal enmeshing. Phospholipid fatty acid analysis further confirmed relatively higher abundance of fungi in macroaggregates in straw-containing soil. All in all, our study provides insights into the initial stages of aggregate formation following litter additions and development of associated microbial community. The spatial analysis enabled by the X-ray fluorescence microspectroscopy enabled visualization of internal aggregate structures, shedding light on the processes involved, which is not possible with bulk analysis alone.