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In addition to hydrogen poisoning, efficient electron transfer between promoters and Ru particles plays a crucial role in enhancing the performance of Ru-based heterogeneous catalysts for ammonia synthesis. Traditionally, Ru-based catalysts containing surface promoters prepared via an impregnation method pay significant attention to the contact position between promoter and Ru particles. Previous studies have shown that a minimal amount of surface promoters significantly enhances the activity, but excessive promoters can encapsulate transition metals, reducing the catalytic activity. In this work, we identify a mechanism of bulk Cs promoter that differs from traditional surface cocatalysts. The ammonia synthesis activity of Ru/Cs0.68Ti1.83O4with bulk Cs is seven times higher than that of Cs–Ru/TiO2synthesized by the impregnation method. Low hydrogen poisoning is revealed by kinetics studies while using a bulk Cs promoter. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images confirm no distinct differences of the positions between Cs and Ru for the above catalysts, indicating that the positioning factor is not a key determinant influencing activity. X-ray absorption near-edge structure (XANES) results demonstrate that bulk and surface Cs follow different electron transfer mechanisms in Ru-based catalysts. Density functional theory calculations support the XANES results by showing that the bulk Cs-containing support Cs0.68Ti1.83O4gives the Ru particles additional electrons. This novel electron transfer mechanism provides new ideas for the design and development of cocatalysts in ammonia synthesis.

We demonstrate reversible hydrogel formation by hydrophobic interaction for poly(N-alkyl-N-vinylacetamide)s with 3 mol % of alkyl chains (side chain length = 10, 12, 14, 16, and 18). The polymers dissolve in ethanol and can be cast to thin films in a mold. When immersed in water, they swell and form biocompatible hydrogels. Our synthesis ensures stochastic distribution of the n-alkyl chains along the water-soluble polymer backbone, and even in the case of the relatively long n-alkyl substituents (C18), side-chain crystallization is fully suppressed. Polymers with alkyl substituents of different lengths demonstrate strong differences in the strength of the hydrophobic association. Relatively short alkyl substituents yield hydrogels, which flow upon shearing but still segregate from excess water, i.e., they exhibit syneresis. Longer alkyl substituents yield hydrogels with mechanical properties approaching those of permanently cross-linked hydrogels. Hydrogels were characterized by strain- and stress-controlled rheological experiments. Their rheological properties follow a time–temperature stickiness (TTS) superposition principle, indicating that the side chains serve as sticky substituents that extend the terminal relaxation time according to their hydrophobicity.

Spin-polarized two-dimensional electron gases (2DEGs) at the interfaces of SrTiO3-based correlated oxides have attracted tremendous attention in electronics and spintronics. Hitherto, the transition temperature (TC) for such spin polarization remains very low at around 20 K, seriously restricting further spin-based applications. Here, we demonstrate a new strategy to greatly enhance the spin polarization at the interfaces of the prototypical LaAlO3/SrTiO3by conveniently inserting a SrCoO2.5-patterned Hall-bar layer. In the modified interfacial heterostructure, signatures of spin polarization, such as the Kondo effect, hysteretic magnetoresistance, magnetic hysteresis loop, and anomalous Hall effect, are all unambiguously observed. The TCof spin polarization deduced from the anomalous Hall effect is promoted to a significantly high temperature of 100 K, much higher than any reported values for 2DEGs at oxide interfaces. Combining atomic-level resolution electron energy-loss spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism spectroscopy, the origin of spin polarization is attributed to the occurrence of Ti3+ions located around the interfaces. This work opens up a reliable interfacial engineering route to enhance the spin polarization in 2DEGs at oxide interfaces, which is applicable for practical spin-based logic and memory devices.

Sodium layered oxides are considered to be cathode candidates with the most potential for large-scale energy storage because of their high reversible capacity and wide availability of sodium resources. A significant hurdle to wide application of these layered oxides lies in simultaneously satisfying high-energy density and long cycle life because of the intrinsic problems associated with their structural irreversibility. Herein, a O3/O′3-P2 core–shell composite that integrates a high specific capacity from O-type Ni-based core and good structural stability from P2-type Mn-rich shell is presented. Multiscale electron microscopy and affiliated spectroscopy analyses reveal that, in addition to the microscale O3/O′3-P2 core–shell structure, a nanoscale coherent P2/O3 intergrown structure can also be identified in the composite. Such well-tailored structures not only constrain the structural damages (microscale cracks) induced by repeated volumetric changes upon desodiation and resodiation but also facilitate fast Na ions diffusion through the exterior P2-type layered structure. This work may provide new clues into the design of high-performance cathode materials for sodium-ion batteries.

Advances in personalized medicine will require custom drug formulations and delivery mechanisms. Herein, we demonstrate a new type of personalized capsule comprising of printed concentric cylindrical layers with each layer having a distinctive functional drug component. Poly ε-caprolactone (PCL) with paracetamol (APAP) and chlorpheniramine maleate (CM), synergistic drugs commonly used to alleviate influenza symptoms, are printed as an inner layer and outer layer, respectively, via microscaled electrohydrodynamic (EHD) printing. Polyvinylpyrrolidone (PVP) nanofibers are embedded as interlayers between the two printed PCL-drug layers using electrospinning (ES) techniques. The complete concentric cylindrical capsule with a 6 mm inner diameter and 15 mm length can be swallowed for oral drug delivery. After dissolution of the PVP interlayer, the capsule separates in two, with inner and outer capsules for continuous drug dosing and targeting. Imaging was achieved using a 3T MRI system which allowed temporal observations of the targeted release through the incorporation of nanoparticles (Fe3O4). The morphology and structure, chemical composition, mechanical properties, and biocompatibility of the capsules were studied in vitro. In summary, this new type of custom printed and electrospun capsule that enabled component separation, targeted drug release may advance personalized medicine via multidrug oral delivery.

Two-dimensional (2D) materials such as graphene and transition-metal dichalcogenides reveal the electronic phases that emerge when a bulk crystal is reduced to a monolayer1–4. Transition-metal oxide perovskites host a variety of correlated electronic phases5–12, so similar behaviour in monolayer materials based on transition-metal oxide perovskites would open the door to a rich spectrum of exotic 2D correlated phases that have not yet been explored. Here we report the fabrication of freestanding perovskite films with high crystalline quality almost down to a single unit cell. Using a recently developed method based on water-soluble Sr3Al2O6as the sacrificial buffer layer13,14we synthesize freestanding SrTiO3and BiFeO3ultrathin films by reactive molecular beam epitaxy and transfer them to diverse substrates, in particular crystalline silicon wafers and holey carbon films. We find that freestanding BiFeO3films exhibit unexpected and giant tetragonality and polarization when approaching the 2D limit. Our results demonstrate the absence of a critical thickness for stabilizing the crystalline order in the freestanding ultrathin oxide films. The ability to synthesize and transfer crystalline freestanding perovskite films without any thickness limitation onto any desired substrate creates opportunities for research into 2D correlated phases and interfacial phenomena that have not previously been technically possible.

Yolk–shell particles (YSPs) have attracted increasing attention from various research fields because of their low density, large surface area, and excellent loading capacity. However, the fabrication of polymer-based porous YSPs remains a great challenge. In this work, multifunctional polycaprolactone YSPs were produced using trineedle coaxial electrospraying with a simple nonsolvent process. TiO2–Ag nanoparticles and Ganoderma lucidumpolysaccharides (GLPs) were encapsulated into the outer shell of the YSPs as the major antibacterial and antioxidant components, whereas iron oxide (Fe3O4) nanoparticles were incorporated into the inner core to act as a photothermal agent. The morphology and structure, chemical composition, biocompatibility, antioxidant, and antibacterial effects of the fabricated YSPs, photothermal effects, and the release profile of the encapsulated GLP were studied in vitro. Furthermore, the in vivo wound healing effects of the YSPs and the laser-assisted therapy were explored based on a burn wound model on c57 mice.

Multilayered structured organic particles have had an extensive impact on a wide array of biomedical applications not limited to drug delivery, imaging, and biosensing. A tri-needle coaxial electrospraying system was utilized to engineer multilayered polymeric particles in a one-step, facile process at ambient temperatures. The effect of the dominant processing parameters on the development of a conical cusp that eventually ejects an ultrathin liquid ligament was first explored here. Subsequently, the validation of the intermediate solutions that possessed different conductivities on stabilizing jetting modes and the resulting particle morphology was also investigated. Polycaprolactone (PCL) solutions with different molecular weights were selected as the outer layer using fluids with various conductivities. Five different formulations were studied as the intermediate layers: PCL in acetic acid, ethyl cellulose in acetic acid, ethyl cellulose in dichloromethane, ethyl cellulose in ethanol, and silicone oil and polyvinyl pyrrolidone in water. The results systematically demonstrated that the processing parameters (type of polymer, polymer molecular weight, solution concentration, flow rate, applied voltage, and collector distance) play a significant role in the formation of the stable Taylor cone. This study further identified that the coaxial arrangement of three needles successfully produced multilayered microspheres with uniform size distribution.

Particulate platforms capable of delivering multiple actives as well as providing diagnostic features have gained considerable interest over the last few years. In this study, magnetic polymer yolk–shell particles (YSPs) were engineered using a tri-needle coaxial electrospraying technique enabling dual-mode (ultrasonic and magnetic resonance) imaging capability with specific multidrug compartments via an advanced single-step encapsulation process. YSPs comprised magnetic Fe3O4nanoparticles (MNPs) embedded in the polymeric shell, an interfacing oil layer, and a polymeric core (i.e., composite shell–oil interface–polymeric core). The frequency of the ultrasound backscatter signal was modulated through YSP loading dosage, and both T1- and T2-weighted magnetic resonance imaging signal intensities were shown to decrease with increasing MNP content (YSP outer shell). Three fluorescent dyes (selected as model probes with varying hydrophobicities) were coencapsulated separately to confirm the YSP structure. Probe release profiles were tuned by varying power or frequency of an external auxiliary magnetic field (AMF, 0.7 mT (LAMF) or 1.4 mT (HAMF)). In addition, an “inversion” phenomenon for the AMF-enhanced drug release process was studied and is reported. A low YSP cytotoxicity (5 mg/mL) and biocompatibility (murine, L929) was confirmed. In summary, magnetic YSPs demonstrate timely potential as multifunctional theranostic agents for dual-imaging modality and magnetically controlled coactive delivery.

Critical limb ischemia (CLI) is the most severe clinical manifestation of peripheral arterial disease, which causes many amputations and deaths. Conventional treatment strategies for CLI (e.g., stent implantation and vascular surgery) bring surgical risk, which are not suitable for each patient. Extracellular vesicles (EVs) can be a potential solution for CLI. Herein, vascular endothelial growth factor (VEGF; i.e., a crucial molecule related to angiogenesis) and transcription factor EB (TFEB; i.e., a pivotal regulator of autophagy) are chosen as the target gene to improve the bioactivity of EVs derived from endothelial cells. The VEGF/TFEB‐engineered EVs (Engineered‐EVs) are fabricated by genetically engineering the parent cells, and their versatile functions are confirmed using three cell models (human umbilical vein endothelial cells, myoblast, and monocytes). Injectable thermal‐responsive hydrogel are then combined with Engineered‐EVs to combat CLI. These results reveal that the hydrogel can enhance the stability of Engineered‐EVs in vivo and release EVs at different temperatures. Moreover, the results of animal studies indicate that Engineered‐EV/Hydrogel can significantly improve neovascularization, attenuate muscle injury, and recover limb function after CLI. Finally, mechanistic studies shed light on the therapeutic effect of Engineered‐EV/Hydrogel due to the activated VEGF/VEGFR pathway and autophagy‐lysosomal pathway. The vascular endothelial growth factor (VEGF)/transcription factor EB (TFEB)‐engineered extracellular vesicles (Engineered‐EVs) are incorporated with injectable thermal‐responsive hydrogel. This Engineered‐EV/Hydrogel system can effectively improve neovascularization and attenuate muscle injury in the critical limb ischemia animal model. The activation of VEGF/VEGF receptor pathway and autophagy‐lysosomal pathway can be the potential therapeutic mechanism.

The electrode–electrolyte contact issue within the composite electrode layer is a grand challenge for all-solid-state Li batteries. In order to achieve cycling performances comparable to Li-ion batteries based on liquid electrolyte, the aforementioned solid–solid contact not only needs to be sufficiently thorough but also must tolerate repeated cycling. Simultaneously meeting both requirements is rather challenging. Here, we discover that epitaxy may effectively overcome such bottlenecks even when the electrode undergoes repeated phase transitions during cycling. Through epitaxial growth, the perovskite Li0.33La0.56TiO3solid electrolyte was found capable of forming atomically intimate contact with both the spinel Li4Ti5O12and rock-salt Li7Ti5O12. In contrast to conventional expectations, such epitaxial interfaces can also survive repeated spinel-to-rock-salt phase transitions. Consequently, the Li4Ti5O12–Li0.33La0.56TiO3composite electrode based on epitaxial solid–solid contact delivers not only a rate capability comparable to that of the surry-cast one with solid–liquid contact but also an excellent long-term cycling stability.