Superrepellency of underwater hierarchical structures on Salvinia leaf.

Biomimetic superhydrophobic surfaces display many excellent underwater functionalities, which attribute to the slippery air mattress trapped in the structures on the surface. However, the air mattress is easy to collapse due to various disturbances, leading to the fully wetted Wenzel state, while the water filling the microstructures is difficult to be repelled to completely recover the air mattress even on superhydrophobic surfaces like lotus leaves. Beyond superhydrophobicity, here we find that the floating fern, Salvinia molesta, has the superrepellent capability to efficiently replace the water in the microstructures with air and robustly recover the continuous air mattress. The hierarchical structures on the leaf surface are demonstrated to be crucial to the recovery. The interconnected wedge-shaped grooves between epidermal cells are key to the spontaneous spreading of air over the entire leaf governed by a gas wicking effect to form a thin air film, which provides a base for the later growth of the air mattress in thickness synchronously along the hairy structures. Inspired by nature, biomimetic artificial Salvinia surfaces are fabricated using 3D printing technology, which successfully achieves a complete recovery of a continuous air mattress to exactly imitate the superrepellent capability of Salvinia leaves. This finding will benefit the design principles of water-repellent materials and expand their underwater applications, especially in extreme environments.

Theorem on the Compatibility of Spherical Kirigami Tessellations.

We present a theorem on the compatibility upon deployment of kirigami tessellations restricted on a spherical surface with patterned slits forming freeform quadrilateral meshes. We show that the spherical kirigami tessellations have either one or two compatible states, i.e., there are at most two isolated strain-free configurations along the deployment path. The theorem further reveals that the rigid-to-floppy transition from spherical to planar kirigami tessellations is possible if and only if the slits form parallelogram voids along with vanishing Gaussian curvature, which is also confirmed by an energy analysis and simulations. On the application side, we show a design of bistable spherical domelike structure based on the theorem. Our study provides new insights into the rational design of morphable structures based on Euclidean and non-Euclidean geometries.

Multiple configuration transitions of soft actuators under single external stimulus.

Soft actuators have a wide range of applications in medical instruments, soft robotics, 3D electronics, and deployable structures, where configuration transitions are crucial for their function realization. However, most soft actuators can only morph from the initial configuration directly to the final configuration under a single external stimulus. Herein, we report a novel soft actuator by 3D printing parallel strips with crescent cross-sections onto a thin PDMS film. Multiple configuration transitions are observed when the soft actuator swells in ethyl acetate. Four factors, i.e., the geometric asymmetry of the strips, the fabrication-induced heterogeneity of the film, the differential swelling ratios of the strips and the film, and the geometric parameters of the actuator, are demonstrated to synergistically regulate the multiple configuration transitions of the actuator. Particularly, the underlying mechanisms for the configuration transitions are systematically investigated through experiments and theoretical analysis, and verified via finite element simulation. Benefitting from the multiple configuration transitions, the grasp-release-re-grab function of the actuator is demonstrated under a single stimulus. This work contributes to fundamental understanding of the morphing behaviors and the novel design of soft actuators.

Physically Entangled Antiswelling Hydrogels with High Stiffness.

Physically cross-linked hydrogels have great potential for tissue engineering because of their excellent biocompatibility and easy fabrication. However, physical cross-linking points are typically weaker compared to chemical ones and therefore cannot form robust hydrogels with excellent water stability, which greatly hinder their further applications. In this work, a novel hydrogel with high stiffness and outstanding antiswelling performance cross-linked by hydrophobic polymer chains entanglements is reported. The hydrophobic polymer polyimide (PI) is mixed with the hydrophilic polymer poly-(vinyl pyrrolidone) (PVP) to form cross-linking points between the chains. At the equilibrium swelling state, tensile modulus of the hydrogel can be up to 22.57 MPa (higher than most existing hydrogels) and the equilibrium water swelling ratio (ESR) can be as low as 125.0%. By decreasing the PI mass ratio, tensile modulus and ESR of the hydrogel can be tuned in a wide range from 22.57 to 0.005 MPa and 125.0% to 765.6%, respectively. Using PVP/PI solutions as inks, uniform structures and multi-material structures are fabricated having mechanical properties close to cartilage through a direct ink writing 3D printing platform. This current work demonstrates that entangled PVP/PI hydrogels have excellent tailoring capabilities and are promising candidates for tissue engineering applications.

A Light-Up Strategy with Aggregation-Induced Emission for Identification of HIV-I RNA-Binding Small Molecules.

Fluorescence methods are important tools to identify RNA-binding small molecules and further employed to study RNA-protein interactions. Most reported fluorescence strategies are based on covalent labeling of ligand or RNA, which can impede the binding between them to some extent, or light-off fluorescent indicator displacement methods, which ask for particular indicators. Herein, a label-free fluorescence strategy based on the light-on aggregation-induced emission (AIE) feature of tetraphenylethene (TPE) derivative to screen RNA-binding small molecules is presented. As a result of electrostatic interaction, the selected peptides can induce self-assembly of the TPE derivative to produce strong fluorescent emission; when the peptides are bound to RNA molecules, the TPE derivative is in the deaggregated form and shows no or minimum fluorescence. Based on the phenomenon, a competitive displacement assay combined with the TPE reporter was employed to characterize selected small molecules for their binding abilities to HIV-I RNAs. This AIE feature enables the fluorescence-off state of the TPE derivative in the presence of RNA-peptide complex to be "lightened up" quickly as the RNA-binding molecule is introduced and the peptide is competitively released. This strategy was carried out to test several small molecule binders, and the results are consistent with previous reports. This report gives an inspiring example of AIE-based fluorescent assay for HIV-I RNA-binding molecule screening, which may further be explored to build a drug screening platform for RNA-protein interference.

Unified Model for Size-Dependent to Size-Independent Transition in Yield Strength of Crystalline Metallic Materials.

Size-dependent yield strength is a common feature observed in miniaturized crystalline metallic samples, and plenty of studies have been conducted in experiments and numerical simulations to explore the underlying mechanism. However, the transition in yield strength from bulklike to size-affected behavior has received less attention. Here a unified theoretical model is proposed to probe the yield strength of crystalline metallic materials with sample size from nanoscale to macroscale. We show that the transition in yield strength versus size can be fully explained by the competition between the stresses required for dislocation source activation and dislocation motion, which is regulated by dislocation density, irradiation defect, grain boundary, and so on. Based on various grain boundary densities, the extended Hall-Petch relation, incorporated into the unified model, captures the reverse size effect for polycrystalline samples. The proposed model predictions agree well with reported experimental measurements of various specimens, including the prestrained nickel, irradiated copper, ultrafine grain tungsten, and so on.

Ligand-RNA interaction assay based on size-selective fluorescence core-shell nanocomposite.

The application of the dye-labeled fluorescence method in a ligand-RNA interaction assay is a complex and costly process prone to steric hindrance. Fluorescent nanomaterials offer an attractive alternative due to their simple, low-cost synthesis and effective screening properties. Here, CdTe@ZIF-8 core-shell nanocomposites were used as fluorescence signal transducer in the ligand-TAR RNA interaction assay. Different experimental strategies were developed based on the size-selective nature of the CdTe@ZIF-8 nanocomposites. When ligands can quench fluorescence, two assays of fluorescence recovery with TAR RNA and Tat peptide competitive displacement are carried out successively, which can not only distinguish ligands binding to TAR RNA but also screen potential Tat protein antagonists. When ligands cannot quench fluorescence, the mitoxantrone-TAR RNA complex is used in the competitive displacement assay. Ligands that displaced mitoxantrone from the mitoxantrone-TAR RNA complex signaled the interaction with TAR RNA. Eight ligands, including known and unknown TAR RNA-binding ligands, were tested via the above strategies. The results showed that this method was effective at distinguishing the known RNA-binding partner and screening the Tat antagonist from the test ligands. This simple and effective strategy is expected to be suitable for actual drug screening. Graphical abstract.

Enhanced biochemical characteristics of ß-glucosidase via adsorption and cross-linked enzyme aggregate for rapid cellobiose hydrolysis.

With proper design, immobilization can be useful tool to improve the stability of enzymes, and in certain cases even their activity, selectivity, productivity and economic viability. An immobilized ß-glucosidase (BGL, EC 3.2.1.21) through matrix adsorption and cross-linked enzyme aggregate (ad-CLEA) technology is presented in this work. After adsorption and precipitation, BGL was immobilized to poly(glycidyl methacrylate-co-ethylenedimethacrylate) (PGMA/EDMA) microparticles using glutaraldehyde as the cross-linker. Immobilized BGL exhibits lower apparent Km but much higher Vmax than that of the soluble enzyme, suggesting greater enzyme-substrate affinity and rapid velocity. Besides, ad-CLEA-BGL presents better thermostability retaining activity nearly 70% for 3 h and approximately 50% for 5 h at 70 °C, high operational reusability remaining more than 90% activity after nine uses and excellent storage stability holding about 95% activity after 45 days. Furthermore, the cellobiose is completely hydrolyzed within 1 h with ad-CLEA-BGL, which is significantly more efficient than soluble enzyme (about 4 h). Therefore, BGL was successfully immobilized on PGMA/EDMA microparticles with an ad-CLEA technology and the immobilization greatly enhances the biochemical characteristics. This work indicates promising application for ad-CLEA-BGL in utilizing agricultural remnants, bio-converting cellobiose to fermentable reducing sugar and ethanol production.

Effect of Thermal Conductivity on Enhanced Evaporation of Water Droplets from Heated Graphene-PDMS Composite Surfaces.

The dynamics of evaporating water droplets on heated graphene-poly(dimethylsiloxane) (PDMS) composites is investigated experimentally and theoretically. By inserting graphene nucleates in PDMS, we report the effect of change in thermal resistance on the evaporation process of water droplets on the heated graphene-PDMS composite surface. By dispersing graphene within the PDMS matrix, the evaporation of water droplets is enhanced. The graphene nucleate density over the surface was controlled by varying graphene wt % from 0 to 2%, which in turn controls the thermal resistance and hence the evaporation rate. Experimentally, the maximum evaporation rate of 0.0044 µL/s was observed for the sample of 2 wt % graphene-PDMS composite. The evaporation rate on a 2 wt % graphene-PDMS composite surface is about 1.5 times higher compared to that of plain PDMS without graphene. A theoretical model confirms that the initial contact angle and the presence of thermal coupling between liquid droplets and the substrate play an important role in evaporation dynamics. Thermal conductance increases 3 times with the increase in graphene wt % from 0.1 to 2.0 wt % in PDMS. The heat-storing capacity of graphene is responsible for the enhanced evaporation. The experimental findings are in good agreement with theoretical results. These samples were found insensitive to degradation and may find potential applications where high efficiency and high heat flux are needed.

Activation of mitophagy in inflamed odontoblasts.

OBJECTIVES: Mitophagy is an important mitochondrial quality control mechanism. In this study, we investigated the mitochondrial damage and mitophagy occurred in inflammatory human dental pulp and lipopolysaccharide-stimulated preodontoblasts. MATERIALS AND METHODS: In dental pulp tissues and lipopolysaccharide-stimulated preodontoblasts, immunofluorescences and Western blot were performed to detect the expression of mitochondrial and mitophagy-related proteins, and autophagy markers were also examined. Reactive oxygen species generated by mitochondria were examined by MitoSOX. Transmission electron microscope (TEM) was used to examine the morphology of mitochondria in lipopolysaccharide-stimulated preodontoblasts. RESULTS: The active fission activity of mitochondria and mitophagy in inflammatory dental pulp was observed. In lipopolysaccharide-treated preodontoblasts, mitophagy-related proteins were also upregulated. Moreover, increased reactive oxygen species in the inflamed preodontoblasts were observed. Additionally, single-membrane autolysosomes containing partially degraded mitochondria with swollen inner membranes in lipopolysaccharide-treated preodontoblasts were observed by TEM. CONCLUSIONS: These results indicate that mitochondria were damaged and mitophagy might be activated to degrade impaired mitochondria in inflamed odontoblasts.

Photothermal properties of plasmonic nanoshell-blended nanofluid for direct solar thermal absorption.

The excitation of localized surface plasmon at the metal nanoparticles can significantly enhance the absorption of solar energy. However, the absorption peak is sharp at the resonant frequency. To achieve a broadband absorption, the blended nanofluid formed by SiO2/Ag nanoshells of different core size and shell thickness is employed. The blended nanofluid has a good solar absorption property, whose extinction spectrum matches the solar spectrum well. The transient temperature response of the nanofluid is simulated. It is found that the photothermal performance of the solar thermal collector is related to the geometric parameters and operation conditions of the solar collector, and the optical and thermophysical properties of nanofluid. As the flow velocity increases, the outlet temperature is gradually reduced. But, the collector efficiency is increased since less heat is lost to the environment via convection as nanofluid flows fast in the channel. In order to obtain a large outlet temperature at high velocity, it can be considered to elongate the channel length. Due to the strong extinction properties of the blended nanofluid, the required volume fraction can be significantly reduced, only 1/10 of that of Ag nanofluid for an equal temperature increases.

Ultimate Stable Underwater Superhydrophobic State.

Underwater metastability hinders the durable application of superhydrophobic surfaces. In this work, through thermodynamic analysis, we theoretically demonstrate the existence of an ultimate stable state on underwater superhydrophobic surfaces. Such a state is achieved by the synergy of mechanical balance and chemical diffusion equilibrium across the entrapped liquid-air interfaces. By using confocal microscopy, we in situ examine the ultimate stable states on structured hydrophobic surfaces patterned with cylindrical micropores in different pressure and flow conditions. The equilibrium morphology of the meniscus is tuned by the dissolved gas saturation degree within a critical range at a given liquid pressure. Moreover, with fresh lotus leaves, we prove that the ultimate stable state can also be realized on randomly rough superhydrophobic surfaces. The finding here paves the way for applying superhydrophobic surfaces in environments with different liquid pressure and flow conditions.

Influence of fluid flow on the stability and wetting transition of submerged superhydrophobic surfaces.

Superhydrophobic surfaces have attracted great attention for drag reduction application. However, these surfaces are subject to instabilities, especially under fluid flow. In this work, we in situ examine the stability and wetting transition of underwater superhydrophobicity under laminar flow conditions by confocal microscopy. The absolute liquid pressure in the flow channel is regulated to acquire the pinned Cassie-Baxter and depinned metastable states. The subsequent dynamic evolution of the meniscus morphology in the two states under shear flow is monitored. It is revealed that fluid flow does not affect the pressure-mediated equilibrium states but accelerates the air exchange between entrapped air cavities and bulk water. A diffusion-based model with varying effective diffusion lengths is used to interpret the experimental data, which show a good agreement. The Sherwood number representing the convection-enhanced mass transfer coefficient is extracted from the data, and is found to follow a classic 1/3-power-law relation with the Reynolds number as has been discovered in channel flows with diffusive boundary conditions. The current work paves the way for designing durable superhydrophobic surfaces under flow conditions.

Receding dynamics of contact lines and size-dependent adhesion on microstructured hydrophobic surfaces.

The microstructure size on textured surfaces of a given solid fraction exhibits an important effect on their properties. To understand the size effect on surface adhesion, we study the receding dynamics of the microscopic three-phase contact lines, the adhesive properties, and the relation between them on microstructured surfaces. Two types of surfaces are used, which are micropillar and micropore, respectively. First, the receding process of the contact line is directly observed by laser scanning confocal microscopy (LSCM), which shows distinct characteristics on the two types of surfaces. The micro contact line experiences pinnning, sliding, and rupture on micropillar-patterned surfaces while no rupture occurs on micropore-patterned surfaces. The three-dimensional morphology of the micromeniscus on the micropillared surfaces and the two-dimensional scanning of the cross-sections of the micromeniscus along the diagonal direction are imaged. Based on the images, the local contact angles around the micropillar at the receding front, and the curvatures of the micro-meniscus are obtained. Then, the adhesive force on these surfaces is measured, which surprisingly shows an increasing trend with the size of the microstructure for micropillared surfaces but no obvious size dependence for micropored surfaces. Wetting hysteresis is also measured to testify the similar trend with the size for the two types of surfaces. Further investigation shows that the monotonic increase of the adhesive force with the increasing size of micropillars is due to the growing difficulty of the detachment of the contact lines. The underlying mechanism responsible for the size dependence of the adhesive force is the enhancement of the local reduced pressure exerted on the top of the micropillar with increasing size, resulting from the concave profile of the outer micromeniscus.

Liquid plasticine: controlled deformation and recovery of droplets with interfacial nanoparticle jamming.

Air-exposed droplet systems are widely applied in material preparation and experimental design. Recently, a droplet system with unusual properties featured by a liquid-like appearance and solid-like deformability was produced. However, it was then just an interesting and perplexing phenomenon in the absence of basic understandings and clear perspectives for applications. Here we reveal that stable droplet deformation is attributed to monolayer nanoparticle jamming at the water/vapor interface, and that the normal shape can be recovered by jamming relieving. The degree of jamming affects the droplet shape and transparency and can be tuned by the squeezing force and droplet volume. Using these properties and control methods, we develop the deformed droplet into "liquid plasticine" with predesigned shapes, super-high transparency, and arbitrarily large volume. We demonstrate that liquid plasticine could be used as liquid lenses, channel-like containers, and miniature reactors.

How solid-liquid adhesive property regulates liquid slippage on solid surfaces?

The influence of solid-liquid adhesive property on liquid slippage at solid surfaces has been investigated using experiment approach on well-defined model surfaces as well as theoretical analysis. Based on a classical molecular-kinetic description for molecular and hydrodynamic slip, we propose a simple theoretical model that directly relates the liquid slip length to the liquid adhesive force on solid surfaces, which yields an exponential decay function. Well-defined smooth surfaces with varied surface wettability/adhesion are fabricated by forming self-assembled monolayers on gold with different mole ratios of hydrophobic and hydrophilic thiols. The adhesive force of a water droplet and the molecular slippage on these surfaces are probed by surface force apparatus and quartz crystal microbalance measurements, respectively. The experiment results are well consistent with our theoretical prediction. Our finding benefits the understanding of the underlying mechanism of liquid slippage on solid surfaces at molecular level and the rational design of microfluidics with an aim to be frictionless or highly controllable.

Symmetric and asymmetric meniscus collapse in wetting transition on submerged structured surfaces.

The wetting transition from the Cassie-Baxter to the Wenzel state is a phenomenon critically pertinent to the functionality of microstructured superhydrophobic surfaces. This work focuses on the last stage of the transition, when the liquid-gas interface touches the bottom of the microstructure, which is also known as the "collapse" phenomenon. The process was examined in situ on a submerged surface patterned with cylindrical micropores using confocal microscopy. Both symmetric and asymmetric collapses were observed. The latter significantly shortens the progression of the metastable state prior to the collapse when compared with the former and hence may affect the lifespan of superhydrophobicity. Further experiments identified that asymmetric collapse were induced by impurities due to prior use of the structure. The problem is thus of broad relevance, since endurance through cycles is a practical requirement for these functional surfaces. Finally, the use of hierarchical structures is proposed as a remedy. The embedded self-cleaning mechanism serves to effectively remove the impurities, so as to avoid the triggering mechanism for asymmetric collapses.

Metastable states and wetting transition of submerged superhydrophobic structures.

Superhydrophobicity on structured surfaces is frequently achieved via the maintenance of liquid-air interfaces adjacent to the trapped air pockets. These interfaces, however, are subject to instabilities due to the Cassie-Baxter-to-Wenzel transition and total wetting. The current work examines in situ liquid-air interfaces on a submerged surface patterned with cylindrical micropores using confocal microscopy. Both the pinned Cassie-Baxter and depinned metastable states are directly observed and measured. The metastable state dynamically evolves, leading to a transition to the Wenzel state. This process is extensively quantified under different ambient pressure conditions, and the data are in good agreement with a diffusion-based model prediction. A similarity law along with a characteristic time scale is derived which governs the lifetime of the air pockets and which can be used to predict the longevity of underwater superhydrophobicity.

Novel planar-structure electrochemical devices for highly flexible semitransparent power generation/storage sources.

Flexible and transparent power sources are highly desirable in realizing next-generation all-in-one bendable, implantable, and wearable electronic systems. The developed power sources are either flexible but opaque or semitransparent but lack of flexibility. Therefore, there is increasing recognition of the need for a new concept of electrochemical device structure design that allows both high flexibility and transparency. In this paper, we present a new concept for electrochemical device design--a two-dimensional planar comb-teeth architecture on PET substrate--to achieve both high mechanical flexibility and light transparency. Two types of prototypes--dye-sensitized solar cells and supercapacitors--have been fabricated as planar devices and demonstrated excellent device performance, such as good light transparency, excellent flexibility, outstanding multiple large bending tolerance, light weight, effective prevention of short circuits during bending, and high device integration with up-date microelectronics, compared to conventional sandwich structure devices. Our planar design provides an attractive strategy toward the development of flexible, semitransparent electrochemical devices for fully all-in-one elegant and wearable energy management.

Mode-coupled perturbation growth on the interfaces of cylindrical implosion: A comparison between theory and experiment.

We present a mode-coupled weakly nonlinear model for the evolution of perturbations on cylindrical multilayered shells in a decelerating implosion. We show that nonlinear mode-mode interactions among large wave-number fundamental modes are able to induce the growth of small wave number harmonic modes, i.e., forming inverse cascade channels in the wave-number space. When uniform compression and interfacial coupling are taken into consideration, the amplitude of some perturbation modes exhibits an oscillatory growth pattern, which is beyond the intuition that perturbation amplitudes usually have a fast growth tendency in an implosion dominated by the Bell-Plesset effect. Our model accounts well for the previous experiments of Hsing et al. [Hsing et al., Phys. Rev. Lett. 78, 3876 (1997)0031-900710.1103/PhysRevLett.78.3876 and Phys. Plasmas 4, 1832 (1997)1070-664X10.1063/1.872326], which is among the few experiments of multimode multiinterface perturbation development in a cylindrical implosion. In particular, we find that the inverse cascade of modes is the origin of the excitation and growth of the wave number k=2 harmonic mode on the inner interface. The observed decrease of the fundamental modes on the inner interface is mainly attributed to the decreasing period of the oscillatory growth process. These results may afford further insight into the distortion of hot spots in inertial confined fusion implosion near the final stage, and also help to design multimode perturbation experiments in converging geometry in the coming future.