Biomaterials currently used in cardiac tissue engineering have certain limitations, such as lack of electrical conductivity and appropriate mechanical properties, which are two parameters playing a key role in regulating cardiac cellular behavior. In this work, we engineered myocardial tissue constructs based on reduced graphene oxide (rGO)-incorporated gelatin methacrylyol (GelMA) hybrid hydrogels. The incorporation of rGO into the GelMA matrix significantly enhanced the electrical conductivity and mechanical properties of the material. Moreover, cells cultured on composite rGO-GelMA scaffolds exhibited better biological activities such as cell viability, proliferation, and maturation compared to ones cultured on GelMA hydrogels. Cardiomyocytes showed stronger contractility and faster spontaneous beating rate on rGO-GelMA hydrogel sheets compared to those on pristine GelMA hydrogels, as well as GO-GelMA hydrogel sheets with similar mechanical property and particle concentration. Our strategy of integrating rGO within a biocompatible hydrogel is expected to be broadly applicable for future biomaterial design to improve tissue engineering outcomes. The engineered cardiac tissue constructs using rGO incorporated hybrid hydrogels can potentially provide high-fidelity tissue models for drug studies and the investigations of cardiac tissue development and/or disease processes in vitro.

Keywords: high-valence Ni 3+ , hierarchical porous structure, Ni3S4, oxygen evolution reaction, durability 2 Electrochemical water splitting is a common way to produce hydrogen gas, but the sluggish kinetics of oxygen evolution reaction (OER) significantly limits the overall energy conversion efficiency of the water splitting. In this work, a highly active and stable, meso-macro hierarchical porous Ni3S4 architecture, enriched in Ni 3+ was designed as an advanced electrocatalyst for OER. The obtained Ni3S4 architectures exhibit a relatively low overpotential of 257 mV at 10 mA cm −2 , and 300 mV at 50 mA cm −2 . Additionally, this Ni3S4 catalyst has excellent long-term stability (no degradation after 300 h at 50 mA cm −2 ). The outstanding OER performance is due to the high concentration of Ni 3+ and the meso-macro hierarchical porous structure. The presence of Ni 3+ enhances the chemisorption of OH − which facilitates the electron transfer to the surface during OER. The hierarchical porosity increases the number of exposed active sites, and facilitates mass transport. A water-splitting electrolyzer using the prepared Ni3S4 as the anode catalyst and Pt/C as the cathode catalyst achieved a low cell voltage of 1.51 V at 10 mA cm −2 . Therefore, this work provides a new strategy for the rational design of highly active OER electrocatalysts with high valence Ni 3+ and hierarchical porous architectures.

Direct numerical simulations are employed to examine gravity wave instability dynamics at a high intrinsic frequency, wave amplitudes both above and below nominal convective instability, and a Reynolds number sufficiently high to allow a fully developed turbulence spectrum. Assumptions include no mean shear, uniform stratification, and a monochromatic gravity wave to isolate fluxes due to gravity wave and turbulence structures from those arising from environmental shears or varying wave amplitudes. The results reveal strong wave breaking for both wave amplitudes, severe primary wave amplitude reductions within ;1 or 2 wave periods, an extended turbulence inertial range, significant excitation of additional wave motions exhibiting upward and downward propagation, and a net positive vertical potential temperature flux due to the primary wave motion, with secondary waves and turbulence contributing variable and negative potential temperature fluxes, respectively. Turbulence maximizes within ;1 buoyancy period of the onset of breaking, arises almost entirely owing to shear production, and decays rapidly following primary wave amplitude decay. Secondary waves are excited by wave-wave interactions and the turbulence dynamics accompanying wave breaking; they typically have lower frequencies and smaller momentum fluxes than the primary wave following breaking.

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This paper examines the character, intermittency, and anisotropy of turbulence accompanying wave instability, breaking, and turbulence evolution and decay for gravity waves (GW) having a high intrinsic frequency, amplitudes above and below nominal convective instability, and a high Reynolds number. Wave breaking at both amplitudes leads to an extended inertial range of turbulence, with turbulence energies that maximize within ;1 wave period of the onset of breaking. Turbulence sources include both shear and buoyancy, with shear being the major contributor. Turbulence displays considerable intermittency both within and across the phase of the breaking gravity wave and exhibits clear anisotropy throughout the evolution. Turbulence anisotropy is found at all spatial scales and all times but is most pronounced in the most statically stable phase of the GW and at late times as the turbulent flow restratifies.