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Abstract: Objectives: Biomimetic hydroxyapatite (HAp)-based composites are promising materials for dental restorations due to their hierarchical structure and similarity to natural dental tissues. This study aims to investigate the three-dimensional crystallographic organization of HAp within nacre-inspired composites and to evaluate how different polymers infiltrations influence the structural orientation. Methods: Nacre-inspired HAp ceramic scaffolds were fabricated via bidirectional freeze-casting and subsequently infiltrated with different polymers, including Polyurethane (PU), Poly(methyl methacrylate) (PMMA), Epoxy, and Urethane dimethacrylate (UDMA). The three-dimensional structural organization and crystallite orientation of these composites were investigated using synchrotron-based 3D SAXS tensor tomography (3D SASTT), complemented by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Results: The results reveal distinct differences in crystallite alignment among the composites. HAp/PU exhibits the highest degree of preferred orientation (∼0.7–0.8), whereas HAp/PMMA and HAp/Epoxy show lower alignment values (∼0.2–0.4). The HAp/UDMA composite displays heterogeneous orientation with localized regions of moderate alignment. SEM and EDX analyses confirm variations in lamellar morphology, polymer infiltration, and porosity distribution across the composites. Significance: These findings demonstrate that 3D SASTT enables quantitative mapping of nanoscale crystallite orientation within bulk biomimetic scaffolds and provides new insights into the hierarchical structure of composites, supporting structural design of advanced dental restorative materials.

Open Access

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Abstract: The sterile alpha and TIR motif containing 1 (SARM1) enzyme is a key driver of axonal degeneration in response to injury, making it an attractive target for treating chemotherapy-induced peripheral neuropathy (CIPN) and other nervous system diseases. In this study, we identified and optimised a class of base-exchange inhibitors (BEXi) targeting human SARM1 and explored their molecular interactions and conformational effects using cryo-EM, HDX-MS and SAXS. Although BEXi produced robust inhibition across all biochemical and cellular assay formats, application at sub-inhibitory concentrations consistently led to paradoxical SARM1 activation, and in neuronal assays, accelerated neurite degeneration. Further analysis showed that BEXi only delayed, rather than prevented, neurite degeneration when applied to primary neuronal cells, even at exceedingly high inhibitor concentrations. These results prompted us to discontinue BEXi development in favour of alternative strategies, underscoring the complexity of SARM1 as a therapeutic target and the need for comprehensive, mechanistically informed screening cascades.

Open Access

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Abstract: Reversible addition-fragmentation chain transfer (RAFT) polymerisation-induced self-assembly (PISA) has emerged as a powerful method for the synthesis of well-defined block copolymer nanoparticles in a single step. By exploiting the amphiphilicity of block copolymers, PISA enables the formation of self-assembled structures such as micelles, worms, and vesicles. In this work, RAFT-PISA in methanol was employed to synthesise thermoresponsive nanoparticles, with a focus on understanding the relationship between polymer composition, self-assembly behaviour, and temperature-dependent solvation transitions. The homopolymerisation of diethylene glycol methyl ether methacrylate (DEGMA) was successfully achieved using RAFT solution polymerisation in methanol, with 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPDT) identified as the most effective chain transfer agent (CTA). Using CPDT, macro-CTAs of poly(diethylene glycol methyl ether methacrylate) (PDEGMA), poly(triethylene glycol methyl ether methacrylate) (PTEGMA), and poly(oligoethylene glycol methyl ether methacrylate) (POEGMA) were synthesised and kinetically analysed. All homopolymerisations exhibited first-order kinetics with respect to monomer concentration, demonstrating controlled radical polymerisation behaviour. These macro-CTAs were subsequently chain-extended via RAFT methanolic dispersion polymerisation with methyl methacrylate (MMA), yielding diblock copolymers. While PDEGMA-based diblocks displayed colloidal instability, PTEGMA-b-PMMA and POEGMA-b-PMMA copolymers exhibited improved stability, forming well-defined nanoparticles. Increasing the PMMA block length induced a morphological transition from spherical micelles to vesicles. However, the polymerisation of POEGMA-b-PMMA showed poor RAFT control, resulting in broad molecular weight distributions and heterogeneous particle formation. Further investigations explored the chain extension of PTEGMA macro-CTAs with styrene (Sty) and methyl methacrylate derivatives (MeMBl). The choice of RAFT agent significantly influenced polymerisation control and nanoparticle morphology, with a CPADB-derived PTEGMA macro-CTA enabling improved RAFT control in PTEGMA-b-PSty diblock copolymers. Notably, PTEGMA-b-PMeMBl represented the first reported case of MeMBl incorporation into a diblock copolymer via PISA, yielding nanoparticles with well-defined size distributions. The thermoresponsive behaviour of PTEGMA-b-PMMA nanoparticles was investigated using turbidity measurements, dynamic light scattering (DLS), and nuclear magnetic resonance (NMR) spectroscopy. Results revealed a dual lower critical solution temperature (LCST)- and upper critical solution temperature (UCST)-type transition, dependent on solvent composition and PMMA core size. Crosslinked particles confirmed that solvation of the PMMA core was essential for thermoresponsive behaviour. Small-angle X-ray scattering (SAXS) and nano differential scanning calorimetry (nanoDSC) further validated particle solvation upon heating. The solvent-dependent nature of the phase transition was examined, with methanol identified as the optimal solvent for preserving thermoresponsive properties, whereas higher water content disrupted self-assembly. Overall, this study provides new insights into the RAFT polymerisation of thermoresponsive block copolymers, elucidating the key factors governing colloidal stability, nanoparticle morphology, and solvent-mediated phase transitions. These findings contribute to the broader development of stimuli-responsive polymeric materials for advanced applications.

Open Access

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Abstract: We report a simple design strategy to introduce lithium-responsiveness into N-capped peptide low-molecular-weight gelators by incorporating the FFD tripeptide motif (FF extended with Asp). Asp adds an oxygen-rich carboxylate residue that enables cation-mediated assembly. In high pH aqueous solutions, 2NapFFD shows a pronounced cation selectivity. Li+ generates highly viscous, shear-thinning solutions with birefringent textures, while other Group 1 metals and bulky organic counterions result in low-viscosity and weakly ordered solutions. SAXS and SANS reveal that the addition of Li+ produces substantially extended micellar structures consistent with long cylindrical assemblies, whereas other monovalent cations lead to the formation of short cylindrical objects. The Li+ selectivity is intrinsic to the FFD sequence, with other aromatic caps tuning packing and mesoscale order. Finally, dialysis-driven Li+ exchange induces gelation and enables us to quantify the Li+ uptake by ICP-OES, illustrating potential for selective lithium capture.

Open Access

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Abstract: Slow skeletal muscles maintain posture and produce graded movement at low metabolic cost. ATP utilization during fixed-end contractions is typically five times slower in slow muscles than in fast muscles from the same species. Mechanical measurements previously suggested that more myosin motors are attached to thin filaments during contraction of slow muscle, which seems incompatible with its high efficiency. We therefore used small-angle X-ray diffraction to provide a structural estimate of the fraction of myosin motors attached to thin filaments in slow muscle. The X-ray signals associated with myosin binding to actin indicate that only ∼10% of myosin motors are actin bound during fixed-end tetani of rat soleus slow muscles, compared with ∼25% in mouse extensor digitorum longus fast muscle. Moreover, X-ray signals associated with the helical organization of OFF myosin motors in the thick filaments show that ∼70% of myosin motors remain in the OFF conformation during tetanic contraction of rat soleus muscle, compared with only 30% in mouse extensor digitorum longus muscle. The much slower force development in soleus muscle also allowed clear separation of early structural changes in thick filaments on activation, some of which are distinct from those reported previously in fast muscles. Moreover, the early structural changes in soleus muscle have about the same amplitude in a twitch and a tetanus, suggesting that they are triggered by thin filament activation rather than thick filament stress and implying a fast signalling pathway between thin and thick filaments.