We use THz time-domain spectroscopy to investigate the far-infrared properties of vanadium dioxide thin films, strain-engineered through epitaxial growth on (100)R TiO2 substrates. The films exhibit ...a large uniaxial tensile strain along the rutile c-axis. X-ray diffraction measurements reveal a structural transition temperature of 340 K, whereas independent THz conductivity measurements yield a metal-insulator transition temperature of 365 K along cR. Analysis of these results suggests a Mott-Hubbard behavior along the cR-axis. Along cR the conductivity is approximately 5500 (Ω cm)−1, comparable to bulk single crystals. The tensile strain leads to remarkably uniform cracking oriented along the rutile c-axis, resulting in a large conductivity anisotropy in our single-crystal epitaxial thin films. We discuss our results in the context of previous measurements and calculations of the properties of VO2, under different strain conditions. This work demonstrates the potential of strain engineering to tune the properties of complex materials while also serving as a powerful discriminatory tool for probing microscopic responses.
In this article we study shape-memory behavior of hydrogels, formed by biodegradable and biocompatible recombinant telechelic polypeptides, with collagen-like end blocks and a random coil-like middle ...block. The programmed shape of these hydrogels was achieved by chemical cross-linking of lysine residues present in the random coil. This led to soft networks, which can be stretched up to 200% and “pinned” in a temporary shape by lowering the temperature and allowing the collagen-like end blocks to assemble into physical nodes. The deformed shape of the hydrogel can be maintained, at room temperature, for several days, or relaxed within a few minutes upon heating to 50 °C or higher. The presented hydrogels could return to their programmed shape even after several thermomechanical cycles, indicating that they remember the programmed shape. The kinetics of shape recovery at different temperatures was studied in more detail and analyzed using a mechanical model composed of two springs and a dashpot.
Severe hypoglycemia (SH) is the most frequent and potentially serious complication affecting individuals with type 1 diabetes and can have major clinical and psychosocial consequences. Glucagon is ...the only approved treatment for SH that can be administered by non-health care professionals (HCPs); however, reports on the experiences and emotions of people with type 1 diabetes associated with SH and glucagon rescue use are limited. This survey study demonstrated that an increasing number of individuals with type 1 diabetes have current and filled prescriptions for glucagon and have been educated about glucagon rescue use by an HCP. Despite this positive trend, challenges with SH remain, including a high level of health care resource utilization, considerable out-of-pocket expenses for glucagon kits, a high prevalence of hypoglycemia unawareness, and a negative emotional impact on individuals with diabetes. Nocturnal and exercise-related hypoglycemia were concerns for most survey participants.
In this report, we study the self-assembly of two silk-elastin-like proteins: one is a diblock S24E40 composed of 24 silk-like (S) repeats and 40 elastin-like (E) repeats; the other is a triblock ...S12C4E40 , in which the S and E blocks are separated by a random coil block (C4 ). Upon lowering the pH, the acidic silk-like blocks fold and self-assemble into fibrils by a nucleation-and-growth process. While silk-like polymers without elastin-like blocks form fibrils by heterogeneous nucleation, leading to monodisperse populations, the elastin-like blocks allow for homogeneous nucleation, which gives rise to polydisperse length distributions, as well as a concentration-dependent fibril length. Moreover, the elastin-like blocks introduce temperature sensitivity: at high temperature, the fibrils become sticky and tend to bundle and aggregate in an irreversible manner. Concentrated solutions of S12C4E40 form weak gels at low pH that irreversibly lose elasticity in temperature cycling; this is also attributed to fibril aggregation.
We aimed to identify genetic variants associated with heart failure by using a rat model of the human disease. We performed invasive cardiac hemodynamic measurements in F2 crosses between ...spontaneously hypertensive heart failure (SHHF) rats and reference strains. We combined linkage analyses with genome-wide expression profiling and identified Ephx2 as a heart failure susceptibility gene in SHHF rats. Specifically, we found that cis variation at Ephx2 segregated with heart failure and with increased transcript expression, protein expression and enzyme activity, leading to a more rapid hydrolysis of cardioprotective epoxyeicosatrienoic acids. To confirm our results, we tested the role of Ephx2 in heart failure using knockout mice. Ephx2 gene ablation protected from pressure overload-induced heart failure and cardiac arrhythmias. We further demonstrated differential regulation of EPHX2 in human heart failure, suggesting a cross-species role for Ephx2 in this complex disease.
CoFe2O4 (CFO) epitaxial thin films of various thicknesses were grown on MgO substrates using the pulsed electron-beam deposition technique. The films have excellent in-plane coherence with the ...substrate, exhibit layer-by-layer growth and have well-defined thickness fringes in x-ray diffraction measurements. Atomic force microscopy (AFM) measurements indicate that misfit dislocations form in thicker films and the critical thickness for the dislocation formation is estimated. Perpendicular magnetic anisotropy in CFO due to epitaxial in-plane tensile strain from the substrate was found. A stripe-like domain structure in the demagnetized state is demonstrated using magnetic force microscopy (MFM), in agreement with previous predictions. Coercivity increased in thicker films, which is explained by domain wall pinning due to misfit dislocations at the CFO/MgO interface.
▶ X-ray diffraction and rocking curves indicate films are amongst highest quality in the literature. ▶ Domain structure of CoFe2O4 films on MgO was found to be stripe-like using MFM. ▶ Critical thickness for misfit dislocations estimated and agrees with experiment. ▶ Effect of misfit dislocations on surface morphology explained. ▶ Role of dislocations and antiphase boundaries in domain wall formation and motion explained.
We use multiple particle tracking microrheology to study the melting and gelation behavior of well-defined collagen-inspired designer biopolymers expressed by the transgenic yeast P. Pastoris. The ...system consists of a hydrophilic random coil-like middle block and collagen-like end block. Upon cooling, the end blocks assemble into well-defined transient nodes with exclusively 3-fold functionality. We apply the method of time-cure superposition of the mean-square displacement of tracer beads embedded in the biopolymer matrix to study the kinetics and thermodynamics of approaching the gel point from both the liquid and the solid side. The melting point, gel point, and critical relaxation exponents are determined from the shift factors of the mean-square displacement and we discuss the use of dynamic scaling exponents to correctly determine the critical transition. Critical relaxation exponents obtained for different concentrations in both systems are compared with the currently existing dynamic models in literature. In our study, we find that, while the time scales of gelation and melting are different by orders of magnitude, and show inverse dependence on concentration, that the pathways followed are completely equivalent.
Concerted effects: Triblock peptide copolymers, organic multidentate ligands, and Zn2+ ions associate spontaneously into well‐defined nanoribbons when dissolved at proper ratios in water at moderate ...pH values. These nanofibers are stabilized by an extraordinary concerted effect of distinct noncovalent interactions: metal–ligand complexation, hydrogen bonding, hydrophobic interaction, and polyelectrolyte complexation between coordination polymers and the charged blocks of the peptide copolymers.
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