Photonic response and temperature evolution of SiO2/TiO2 multilayers

The microstructural and optical reflectivity response of photonic SiO₂/TiO₂ nanomultilayers have been investigated as a function of temperature and up to the material system’s melting point. The nanomultilayers exhibit high, broadband reflectivities up to 1350 °C with values that exceed 75% for a 1 μm broad wavelength range (600–1600 nm). The optimized nanometer sized, dielectric multilayers undergo phase transformations from anatase TiO₂ and amorphous SiO₂ to the thermodynamically stable phases, rutile and cristobalite, respectively, that alter their structural morphology from the initial multilayers to that of a scatterer. Nonetheless, they retain their photonic characteristics, when characterized on top of selected substrate foils. The thermal behavior of the nanometer sized multilayers has been investigated by differential thermal analysis (DTA) and compared to that of commercially available, mm-sized, annealed powders. The same melting reactions were observed, but the temperatures were lower for the nm-sized samples. The samples were characterized using X-ray powder diffraction before DTA and after annealing at temperatures of 1350 and 1700 °C. The microstructural evolution and phase compositions were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. The limited mutual solubility of one material to another, in combination with the preservation of their optical reflectivity response even after annealing, makes them an interesting material system for high-temperature, photonic coatings, such as photovoltaics, aerospace re-entry and gas turbines, where ultra-high temperatures and intense thermal radiation are present.

     

A Nanoparticle Ink Allowing the High Precision Visualization of Tissue Engineered Scaffolds by MRI (Small 30/2023)

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with “negative” contrast agents that produce several image artifacts impeding the delineation of the implant's contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T₁-weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of “positive” contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach.     

Organogels versus Hydrogels: Advantages,Challenges, and Applications

Organogels are an important class of gels, and are comparable to hydrogels owing to their properties as liquid-infused soft materials. Despite the extensive choice of liquid media and compatible networks that can provide a broader range of properties, relatively few studies are reported in this area. This review presents the applicability of organogels concerning their choice of components, unique properties, and applications. Their distinctive features compared to other gels are discussed, including multi-stimuli responses, affinity to a broad range of substances, thermal and environmental stability, electronic and ionic conductivity, and actuation. The active role of solvents is highlighted in the versatility of organogel properties. To differentiate between organogels and other gels, these are classified as gels filled with different organic liquids, including highly polar organic solvents and binary solvent systems. Most promising applications of organogels as sophisticated multifunctional materials are discussed in light of their unique features.     

Mitochondrial rRNA Methylation by Mettl15 Contributes to the Exercise and Learning Capability in Mice

Mitochondrial translation is a unique relic of the symbiotic origin of the organelle. Alterations of its components cause a number of severe human diseases. Hereby we report a study of mice devoid of Mettl15 mitochondrial 12S rRNA methyltransferase, responsible for the formation of m⁴C839 residue (human numbering). Homozygous Mettl15^−/− mice appeared to be viable in contrast to other mitochondrial rRNA methyltransferase knockouts reported earlier. The phenotype of Mettl15^−/− mice is much milder than that of other mutants of mitochondrial translation apparatus. In agreement with the results obtained earlier for cell cultures with an inactivated Mettl15 gene, we observed accumulation of the RbfA factor, normally associated with the precursor of the 28S subunit, in the 55S mitochondrial ribosome fraction of knockout mice. A lack of Mettl15 leads to a lower blood glucose level after physical exercise relative to that of the wild-type mice. Mettl15^−/− mice demonstrated suboptimal muscle performance and lower levels of Cox3 protein synthesized by mitoribosomes in the oxidative soleus muscles. Additionally, we detected decreased learning capabilities in the Mettl15^−/− knockout mice in the tests with both positive and negative reinforcement. Such properties make Mettl15^−/− knockout mice a suitable model for mild mitochondriopathies.     

Characterization of a Novel Amphiphilic Cationic Chlorin Photosensitizer for Photodynamic Applications

A novel amphiphilic cationic chlorin e₆ derivative was investigated as a promising photosensitizer for photodynamic therapy. Two cationic –N(CH₃)₃⁺ groups on the periphery of the macrocycle provide additional hydrophilization of the molecule and ensure its electrostatic binding to the mitochondrial membranes and bacterial cell walls. The presence of a hydrophobic phytol residue in the same molecule results in its increased affinity towards the phospholipid membranes while decreasing its stability towards aggregation in aqueous media. In organic media, this chlorin e₆ derivative is characterized by a singlet oxygen quantum yield of 55%. Solubilization studies in different polymer- and surfactant-based supramolecular systems revealed the effective stabilization of this compound in a photoactive monomolecular form in micellar nonionic surfactant solutions, including Tween-80 and Cremophor EL. A novel cationic chlorin e₆ derivative also demonstrates effective binding towards serum albumin, which enhances its bioavailability and promotes effective accumulation within the target tissues. Laser confocal scanning microscopy demonstrates the rapid intracellular accumulation and distribution of this compound throughout the cells. Together with low dark toxicity and a rather good photostability, this compound demonstrates significant phototoxicity against HeLa cells causing cellular damage most likely through reactive oxygen species generation. These results demonstrate a high potential of this derivative for application in photodynamic therapy.     

Toward the Prediction and Control of Glass Transition Temperature for Donor–Acceptor Polymers

Semiconducting donor–acceptor (D–A) polymers have attracted considerable attention toward the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications. Here, polydiketopyrrolopyrrole (PDPP)‐based D–A polymers with varied alkyl side‐chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (T_g) with increasing side‐chain length, which is further verified through coarse‐grained molecular dynamics simulations. Informed from experimental results, a mass‐per‐flexible bond model is developed to capture such observation through a linear correlation between T_g and polymer chain flexibility. Using this model, a wide range of backbone T_g over 80 °C and elastic modulus over 400 MPa can be predicted for PDPP‐based polymers. This study highlights the important role of side‐chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict T_g and elastic modulus of future new D–A polymers.     

Synthesis‐Gas Absorption under Real Process Conditions: Thermodynamic Aspects

The solubility of synthesis gas was measured in the temperature range of 100–300 °C and pressure range of 1.0–5.0 MPa in polar (2‐propanol) and nonpolar (n‐dodecane) solvents. Thermodynamic parameters of the absorption, such as the Henry constant, absorption enthalpy, and apparent activation energy of absorption, were calculated on the basis of the obtained results. The phase equilibrium was calculated by using the Soave‐Redlich‐Kwong cubic equation of state, which could be used to predict the optimal process conditions for liquid‐phase Fischer‐Tropsch reactions in different solvents.     

Inherent Photodegradability of Polymethacrylate Hydrogels: Straightforward Access to Biocompatible Soft Microstructures

Hydrogels are important functional materials useful for 3D cell culture, tissue engineering, 3D printing, drug delivery, sensors, or soft robotics. The ability to shape hydrogels into defined 3D structures, patterns, or particles is crucial for biomedical applications. Here, the rapid photodegradability of commonly used polymethacrylate hydrogels is demonstrated without the need to incorporate additional photolabile functionalities. Hydrogel degradation depths are quantified with respect to the irradiation time, light intensity, and chemical composition. It can be shown that these parameters can be utilized to control the photodegradation behavior of polymethacrylate hydrogels. The photodegradation kinetics, the change in mechanical properties of polymethacrylate hydrogels upon UV irradiation, as well as the photodegradation products are investigated. This approach is then exploited for microstructuring and patterning of hydrogels including hydrogel gradients as well as for the formation of hydrogel particles and hydrogel arrays of well‐defined shapes. Cell repellent but biocompatible hydrogel microwells are fabricated using this method and used to form arrays of cell spheroids. As this method is based on readily available and commonly used methacrylates and can be conducted using cheap UV light sources, it has vast potential to be applied by laboratories with various backgrounds and for diverse applications.     

Ab initio approaches to high-entropy alloys: a comparison of CPA,SQS, and supercell methods

Journal of Materials Science - We present a comparative study of different modeling approaches to the electronic properties of the $$text {Hf}_{0.05}text {Nb}_{0.05}text {Ta}_{0.8}text...