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Abstract: The discovery and development of new adhesive materials is critical for real-world applications of polymeric composite materials. Herein, we report the design and synthesis of a library of structurally related phase-separated supramolecular polyurethanes whose mechanical properties and adhesive characteristics can be enhanced through minor structural modifications of the polymer end-group. The interplay between phase separation of the hard domain polar end-groups and soft polybutadiene domains, coupled with tuneable self-assembly afforded by the polar end-groups, gives rise to a class of materials with tuneable mechanical properties. Exceptionally strong supramolecular adhesives and mechanically robust self-healing elastomers were identified. The mechanical properties were investigated through tensile testing. Finally, rheological analysis of the supramolecular materials was used to identify suitable healing and adhesive temperatures in addition to elucidate the supramolecular polyurethanes' thermal-responsive nature.

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Abstract: Purpose : To elucidate the hierarchical deformation mechanisms of human corneal collagen under controlled inflation of physiological and pathological magnitudes. Methods : 6 human donor corneas with scleral rim were mounted onto a bespoke sealed cell, which was connected via two pressure regulators and an expansion vessel to a source of compressed nitrogen. The cell included a window transparent to X-rays and was connected to translation and rotation stages inside beamline I22 at the Diamond Light Source synchrotron, UK. Images were acquired naso-temporally across the cornea from limbus to limbus at intraocular pressures of 5.5 mmHg, 17.5 mmHg and 40 mmHg. These increments were chosen for comparison with previous static results in the literature and to mimic the normal physiological state and ocular hypertension. Results : The inflation apparatus was able to maintain pressure to an accuracy better than 0.1 mmHg. Features corresponding to collagen fibril diameter, spacing, D-period and orientation as well as tropocollagen spacing and orientation were measured simultaneously. Preliminary analysis revealed a radial distribution of strain (manifested as a change in D-period) across the cornea, which was accentuated in the outer periphery and limbus. In general, the interfibrillar spacing in the periphery and limbus (where collagen fibrils are arranged circumferentially) was found to increase with pressure. Conclusions : The trends in D-period strain are indicative of bulging under increased pressure, which is pronounced at the limbus and the outer periphery. This agrees with the general consensus that the outer periphery and limbus act as a buffer zone, which takes up most of the strain under changes in intraocular pressure, and thus minimises changes in focussing power of the cornea. Further in-depth analysis of this data will allow us to calculate the supramolecular twist (which gives rise to a spring-like stretch in collagen fibrils) and examine in more detail the hierarchical response of corneal collagen to changes in intraocular pressures.

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Abstract: Liposome-based drug delivery systems are widely used to improve drug pharmacokinetics but can suffer from slow and unspecific release of encapsulated drugs. Membrane-active peptides, based on sequences derived or inspired from antimicrobial peptides (AMPs), could offer means to trigger and control the release. Cholesterol is used in most liposomal drug delivery systems (DDS) to improve the stability of the formulation, but the activity of AMPs on cholesterol-rich membranes tends to be very low, complicating peptide-triggered release strategies. Here, we show a de novo designed AMP-mimetic peptide that efficiently triggers content release from cholesterol-containing lipid vesicles when covalently conjugated to headgroup-functionalized lipids. Binding to vesicles induces peptide folding and triggers a lipid phase separation, which in the presence of cholesterol results in high local peptide concentrations at the lipid bilayer surface and rapid content release. We anticipate that these results will facilitate the development of peptide-based strategies for controlling and triggering drug release from liposomal drug delivery systems.

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Abstract: Iron nitride (Fe3N) and iron carbide (Fe3C) nanoparticles can be prepared via sol–gel synthesis. While sol–gel methods are simple, it can be difficult to control the crystalline composition, i.e., to achieve a Rietveld-pure product. In a previous in situ synchrotron study of the sol–gel synthesis of Fe3N/Fe3C, we showed that the reaction proceeds as follows: Fe3O4 → FeOx → Fe3N → Fe3C. There was considerable overlap between the different phases, but we were unable to ascertain whether this was due to the experimental setup (side-on heating of a quartz capillary which could lead to thermal gradients) or whether individual particle reactions proceed at different rates. In this paper, we use in situ wide- and small-angle X-ray scattering (wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS)) to demonstrate that the overlapping phases are indeed due to variable reaction rates. While the initial oxide nanoparticles have a small range of diameters, the size range expands considerably and very rapidly during the oxide–nitride transition. This has implications for the isolation of Rietveld-pure Fe3N, and in an extensive laboratory study, we were indeed unable to isolate phase-pure Fe3N. However, we made the surprising discovery that Rietveld-pure Fe3C nanoparticles can be produced at 500 °C with a sufficient furnace dwell time. This is considerably lower than the previous reports of the sol–gel synthesis of Fe3C nanoparticles.

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Abstract: Fibrotic scarring is prevalent in a range of collagenous tissue disorders. Understanding the role of matrix biophysics in contributing to fibrotic progression is important to develop therapies, as well as to elucidate biological mechanisms. Here, we demonstrate how microfocus small-angle X-ray scattering (SAXS), with in situ mechanics and correlative imaging, can provide quantitative and position-resolved information on the fibrotic matrix nanostructure and its mechanical properties. We use as an example the case of keloid scarring in skin. SAXS mapping reveals heterogeneous gradients in collagen fibrillar concentration, fibril pre-strain (variations in D-period) and a new interfibrillar component likely linked to proteoglycans, indicating evidence of a complex 3D structure at the nanoscale. Furthermore, we demonstrate a proof-of-principle for a diffraction-contrast correlative imaging technique, incorporating, for the first time, DIC and SAXS, and providing an initial estimate for measuring spatially resolved fibrillar-level strain and reorientation in such heterogeneous tissues. By application of the method, we quantify (at the microscale) fibrillar reorientations, increases in fibrillar D-period variance, and increases in mean D-period under macroscopic tissue strains of ~20%. Our results open the opportunity of using synchrotron X-ray nanomechanical imaging as a quantitative tool to probe structure–function relations in keloid and other fibrotic disorders in situ.