Isotropically Polarized Bipiezoelectric Polyacrylonitrile-Poly(vinylidene Fluoride) Advanced Triboelectric Nanogenerator for Operation in High-Humidity Environments.

Conventional hybrid piezo-triboelectric nanogenerators (PTNGs) have potential applications as energy supply devices for microelectronic devices, but their low power density and unstable performance under high-humidity conditions are challenges that need to be solved. Here, we report a novel flexible hybrid bifiezo-triboelectric nanogenerator (Bi-PTNG) based on isotropic polarization design of piezoelectric PVDF and PAN nanofiber membranes, which greatly improves power density of devices and performances in high-humidity conditions. The performance enhancement mechanism of the Bi-PTNG was investigated by model analysis, experimental measurements, and simulations. The results showed that the power density output of Bi-PTNG increased by approximately 88% compared to that of a depolarized PAN/PVDF-based triboelectric nanogenerator (TENG). The application studies demonstrated that a 2 × 2 cm2 Bi-PTNG can be directly used to run more than 120 commercial LEDs, and this highly flexible and breathable all-fiber device can be integrated into clothing or insoles to monitor human movement in high-humidity conditions. This work not only provides an effective strategy for enhancing the power output of TENGs and advancing their practical applications but also offers robust guidance for the material selection and optimization of the polarization direction in such nanogenerators.

Reactive oxygen-scavenging polydopamine nanoparticle coated 3D nanofibrous scaffolds for improved osteogenesis: Toward an aging in vivo bone regeneration model.

Tissue engineered scaffolds aimed at the repair of critical-sized bone defects lack adequate consideration for our aging society. Establishing an effective aged in vitro model that translates to animals is a significant unmet challenge. The in vivo aged environment is complex and highly nuanced, making it difficult to model in the context of bone repair. In this work, 3D nanofibrous scaffolds generated by the thermally-induced self-agglomeration (TISA) technique were functionalized with polydopamine nanoparticles (PD NPs) as a tool to improve drug binding capacity and scavenge reactive oxygen species (ROS), an excessive build-up that dampens the healing process in aged tissues. PD NPs were reduced by ascorbic acid (rPD) to further improve hydrogen peroxide (H2O2) scavenging capabilities, where we hypothesized that these functionalized scaffolds could rescue ROS-affected osteoblastic differentiation in vitro and improve new bone formation in an aged mouse model. rPDs demonstrated improved H2O2 scavenging activity compared to neat PD NPs, although both NP groups rescued the alkaline phosphatase activity (ALP) of MC3T3-E1 cells in presence of H2O2. Additionally, BMP2-induced osteogenic differentiation, both ALP and mineralization, was significantly improved in the presence of PD or rPD NPs on TISA scaffolds. While in vitro data showed favorable results aimed at improving osteogenic differentiation by PD or rPD NPs, in vivo studies did not note similar improvements in ectopic bone formation an aged model, suggesting that further nuance in material design is required to effectively translate to improved in vivo results in aged animal models.

Performance of target irradiation in a high-power laser with a continuous phase plate and spectral dispersion.

We report on the performance of target irradiation at the SG-II high-power laser facility with a continuous phase plate (CPP) and the technique of smoothing by spectral dispersion (SSD). Simulative and experimental results are presented, where the irradiation uniformity and energy concentration of the target spots are analyzed. The results show that the designed CPP can focus the spot energy into the desired region and shape a profile with steep edge and flat top, but the actual performance of the fabricated CPP needs some improvements. It is also proved that the CPP is insensitive to the long-scale wavefront distortion in the incident beam. The one-dimensional SSD configuration evidently works in smoothing the fine-scale intensity modulation inside the target spot.

Numerical simulation of vegetation evolution in compound channels.

The study of vegetation evolution is essential for further understanding of biogeographic feedback and ecological restoration. In this paper, a vegetation evolution model based on velocity threshold (scaled by the average flow velocity of the bare bed) was established to simulate the vegetation evolution process in compound channels. In this model, the effect of vegetation on water flow was generalized as equivalent Manning coefficient, and the velocity field was obtained by solving two-dimensional shallow water equations. The model defined that new vegetation was added in areas where the velocity was less than the velocity threshold, and conversely, vegetation was destroyed in areas where the flow velocity exceeded the velocity threshold. The model was used to explore the effect of velocity threshold, initial vegetation coverage, and relative water depth (the ratio of the flow depth in the floodplain to that over main channel) on final vegetation coverage and longitudinal dispersion coefficient (Ke) in compound channels, and compare the difference of vegetation evolution between rectangular channels and compound channels. Results showed that the velocity threshold played a decisive role in vegetation evolution, and the effect of relative water depth and cross section type on vegetation evolution was only reflected when the velocity threshold was small. The longitudinal dispersion coefficient gradually increased with the expansion of vegetation, and tended to a constant value (Kf) when a stable vegetation landscape was reached. As the relative water depth decreased, the longitudinal dispersion coefficient presented an increasing trend. Regular distribution of initial vegetation patches can produce larger longitudinal dispersion coefficient compared to the cases of random distribution in compound and rectangular channels, and the increasing effect was more significant in compound channels.

Analysis of contaminant dispersion in open channel with two streambank-absorption boundaries.

Boundary absorption intensity can affect the contaminant depletion capacity within rivers, and the process of spatial contaminant cloud expansion is complicated with the consideration of irreversible absorption boundaries at riverbanks. Nonuniformity of concentration distribution appears in spatial concentration distribution, especially in the transverse direction, which is caused by the absorption capacity difference between two riverbanks. A model for illustrating the performance of environmental dispersion with two irreversible absorption banks in 2D space is given in this work. Furthermore, the position of the maximum concentration distributions shifts within the transverse directions with the change of the absorption intensities at two boundaries. The overall absorption capacity would also be affected by the ratio of two absorption intensities at the left and right riverbanks. The residual mass is left with a greater variation in the two bank-absorption intensity ratios. A detailed analysis of the spatial concentration distribution and contaminant depletion capacity with two bank-absorption boundaries would contribute to the construction of a wetland for water treatment. With a certain absorption capacity in total, the transverse distribution of concentration gets more heterogeneous as the ratio deviates from 1gradually, and the transverse concentration distribution appears to be symmetric to the center (0.5W) when the ratios of absorption intensities at two stream-banks are in accord with ß0 : ß1 = ß1 : ß0. The novelty of this work is to provide the analytical solution of two-dimensional concentration distribution with the ratio of two stream-bank absorptions, furthermore, a linear fitting equation([Formula: see text]) for crest position of transverse concentration distribution is given to show the shifting process of spatial contaminant cloud with the change of two stream-bank absorption ratios, and the correlation coefficients are all above 0.99, illustrating a good fit for the results.

Synergy of Porous Structure and Microstructure in Piezoresistive Material for High-Performance and Flexible Pressure Sensors.

A porous and microstructure piezoresistive material composed of polydimethylsiloxane (PDMS) and multiwalled carbon nanotubes (MWCNTs) was designed and prepared for a flexible and highly sensitive pressure sensor over a wide detection range. The microstructure was patterned on the surface of the partially cured PDMS/MWCNTs/NaCl mixture by imprinting a nonwoven fabric. After curing and dissolving the NaCl powders, the porous and surface microstructure PDMS/MWCNT film was obtained. Two PDMS/MWCNT films were stacked together and sandwiched between two copper foil electrodes, in which the two microstructure surfaces were in contact with the electrodes. Due to the synergistic effects of the combination of the porous structure and surface microstructure, the flexible sensor had highly sensitive response over a wide pressure range from 1 Pa to 100 kPa. Under the small pressure, the high sensitivity was achieved by the change in contact areas between the electrodes and the surface microstructures; at high pressure up to 100 kPa, the sensor retained its high sensitivity because of the porous structure of the piezoresistive PDMS/MWCNT material. Additionally, the sensor had fast response speed and good durability. The piezoresistive pressure sensors based on the porous and microstructure PDMS/MWCNTs were demonstrated in detection of sound, monitoring of human activities, and array mapping of the spatial pressure distribution.

Micropatterned Biphasic Nanocomposite Platform for Maintaining Chondrocyte Morphology.

One major limitation hindering the translation of in vitro osteoarthritis research into clinical disease-modifying therapies is that chondrocytes rapidly spread and dedifferentiate under standard monolayer conditions. Current strategies to maintain rounded morphologies of chondrocytes in culture either unnaturally restrict adhesion and place chondrocytes in an excessively stiff mechanical environment or are impractical for use in many applications. To address the limitations of current techniques, we have developed a unique composite thin-film cell culture platform, the CellWell, to model articular cartilage that utilizes micropatterned hemispheroidal wells, precisely sized to fit individual cells (12-18 µm diameters), to promote physiologically spheroidal chondrocyte morphologies while maintaining compatibility with standard cell culture and analytical techniques. CellWells were constructed of 15-µm-thick 5% agarose films embedded with electrospun poly(vinyl alcohol) (PVA) nanofibers. Transmission electron microscope (TEM) images of PVA nanofibers revealed a mean diameter of 60.9 ± 24 nm, closely matching the observed 53.8 ± 29 nm mean diameter of human ankle collagen II fibers. Using AFM nanoindentation, CellWells were found to have compressive moduli of 158 ± 0.60 kPa at 15 µm/s indentation, closely matching published stiffness values of the native pericellular matrix. Primary human articular chondrocytes taken from ankle cartilage were seeded in CellWells and assessed at 24 h. Chondrocytes maintained their rounded morphology in CellWells (mean aspect ratio of 0.87 ± 0.1 vs three-dimensional (3D) control [0.86 ± 0.1]) more effectively than those seeded under standard conditions (0.65 ± 0.3), with average viability of >85%. The CellWell's design, with open, hemispheroidal wells in a thin film substrate of physiological stiffness, combines the practical advantages of two-dimensional (2D) culture systems with the physiological advantages of 3D systems. Through its ease of use and ability to maintain the physiological morphology of chondrocytes, we expect that the CellWell will enhance the clinical translatability of future studies conducted using this culture platform.

Preparation of keratin/PET nanofiber membrane and its high adsorption performance of Cr(VI).

In this study, we prepared wool keratin/PET composite nanofiber membrane to adsorb the Cr(VI) in acidic solution due to its strong adsorption ability. The adsorption ability of the composite membrane with different ratios of keratin to PET was investigated. The optimum adsorption ability can be obtained when the keratin concentration was 50% in the solution with a pH value of 3. With the higher content of keratin, the membrane possessed higher hydrophilicity, larger pore ratio, and larger extent amino protonation. The maximum adsorption ability of the composite membranes was 75.86 mg/g, while that of the pure PET nanofiber membrane was 27.27 mg/g. The FTIR and XPS analysis results demonstrated that both the disulfide bond of the keratin and the amino were involved in the adsorption process. The process was achieved by the electrostatic adsorption of the amino and the redox reaction of disulfide bond in cystine oxide. The removal property of the electrospun keratin/PET composite membrane was 75.86 mg/g.

Aligned electrospun ZnO nanofibers for simple and sensitive ultraviolet nanosensors.

The current of uni-axially aligned electrospun ZnO nanofibers is modulated reversibly under UV irradiation, with the sensitivity of the UV nanosensors depending on the surface coating of the nanofibers, due to the effect on the photo-generated current.

Recent Advances in Flexible and Wearable Pressure Sensors Based on Piezoresistive 3D Monolithic Conductive Sponges.

High-performance flexible strain and pressure sensors are important components of the systems for human motion detection, human-machine interaction, soft robotics, electronic skin, etc., which are envisioned as the key technologies for applications in future human healthcare monitoring and artificial intelligence. In recent years, highly flexible and wearable strain/pressure sensors have been developed based on various materials/structures and transduction mechanisms. Piezoresistive three-dimensional (3D) monolithic conductive sponge, the resistance of which changes upon external pressure or stimuli, has emerged as a forefront material for flexible and wearable pressure sensor due to its excellent sensor performance, facile fabrication, and simple circuit integration. This review focuses on the rapid development of the piezoresistive pressure sensors based on 3D conductive sponges. Various piezoresistive conductive sponges are categorized into four different types and their material and structural characteristics are summarized. Methods for preparation of the 3D conductive sponges are reviewed, followed by examples of device performance and selected applications. The review concludes with a critical reflection of the current status and challenges. Prospects of the 3D conductive sponge for flexible and wearable pressure sensor are discussed.

Tunable Water Delivery in Carbon-Coated Fabrics for High-Efficiency Solar Vapor Generation.

Solar vapor generation by localized heating and evaporation has potential to be a viable and "green" way to produce fresh water. This work reports a carbon black-coated cotton fabric with a tunable water delivery property for high-efficiency solar vapor generation under 1 sun. The fabric is prepared by an electrospray of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) on one-side of the fabric followed by dip-coating of the fabric with carbon black as a photothermal absorber. Depending on the duration of electrospray, the roughness gradient generated by the PVDF-HFP layer in the fabric leads to guided and continuous one-way water transport from the electrosprayed hydrophobic side to the hydrophilic side with a tunable delivery rate. The tunable water delivery capability of the fabric regulates the amount of water supplied to the vicinity of the photothermal absorber. Additionally, the fabric shows excellent broadband absorption and low thermal conductivity. In comparison with the carbon black-coated fabric without a roughness gradient, the regulation of water improves the solar vapor conversion efficiency, owing to reduced heat loss and better heat allocation. Under optimal conditions, a solar vapor conversion efficiency of 88.9% and a stable water evaporation rate of 1.33 kg (m2·h)-1 under 1 sun are achieved.

Preparation, characterization, and encapsulation/release studies of a composite nanofiber mat electrospun from an emulsion containing poly (lactic-co-glycolic acid).

The aim of this study was to investigate the preparation, characterization, and encapsulation/release performance of an electrospun composite nanofiber mat. The hypothesis was that the composite nanofiber mat with nano-scaled drug particles impregnated in biocompatible and biodegradable polymer nanofibers can serve as an innovative type of tissue engineering scaffold with desired and controllable drug encapsulation/release properties. To test the hypothesis, the composite nanofiber mat electrospun from an emulsion consisting of poly (lactic-co-glycolic acid) (PLGA) Rhodamine B (a model compound to simulate drugs), sorbitan monooleate (Span-80, a non-ionic emulsifier/surfactant that is presumably non-toxic/safe for cell-growth), chloroform, DMF, and distilled water was prepared and characterized; and the Rhodamine B encapsulation/release profile in phosphate buffered saline (pH = 7.4) was recorded and analyzed. For comparison purposes, two additional nanofiber mats electrospun from (1) a solution containing PLGA and Rhodamine B, and (2) a solution containing PLGA, Rhodamine B, and Span-80 were also prepared and assessed as the control samples. The results indicated that the composite nanofiber mat electrospun from the emulsion had the most desired and controllable Rhodamine B encapsulation/release profile and the excellent morphological sustainability; thus, it could be utilized as both a drug encapsulation/release vehicle and a tissue engineering scaffold.

Flexible and Compressible PEDOT:PSS@Melamine Conductive Sponge Prepared via One-Step Dip Coating as Piezoresistive Pressure Sensor for Human Motion Detection.

Flexible and wearable pressure sensor may offer convenient, timely, and portable solutions to human motion detection, yet it is a challenge to develop cost-effective materials for pressure sensor with high compressibility and sensitivity. Herein, a cost-efficient and scalable approach is reported to prepare a highly flexible and compressible conductive sponge for piezoresistive pressure sensor. The conductive sponge, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)@melamine sponge (MS), is prepared by one-step dip coating the commercial melamine sponge (MS) in an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Due to the interconnected porous structure of MS, the conductive PEDOT:PSS@MS has a high compressibility and a stable piezoresistive response at the compressive strain up to 80%, as well as good reproducibility over 1000 cycles. Thereafter, versatile pressure sensors fabricated using the conductive PEDOT:PSS@MS sponges are attached to the different parts of human body; the capabilities of these devices to detect a variety of human motions including speaking, finger bending, elbow bending, and walking are evaluated. Furthermore, prototype tactile sensory array based on these pressure sensors is demonstrated.

One-Way Water Transport Fabrics Based on Roughness Gradient Structure with No Low Surface Energy Substances.

Despite great recent progress in one-way water transport (OWT) fabrics, the development of these fabrics based on roughness gradient without low surface energy materials has yet to be achieved. In this work, we prepared OWT fabrics using five polymers with hydrophobic or hydrophilic groups by constructing a roughness gradient structure along the fabric thickness. Electrospraying was used to deposit a rough layer on fabric's single side. The surface energy gradient change across the fabric thickness derived from roughness gradient structure played a major part in determining the OWT performance. With the roughness gradient structure, even polymers with hydrophilic groups, such as polyacrylonitrile and polyamide 6, could become OWT fabrics. Besides, the layer deposited on the surface of the fabric showed no effects on the air permeability of the fabric. These novel results provided an opportunity for more polymers, especially for hydrophilic polymers, to be used to prepare OWT fabrics by designing a roughness gradient along the thickness of the fabric. The method would be applied in designing of OWT fabrics with high performance.

One-Step Preparation of Highly Hydrophobic and Oleophilic Melamine Sponges via Metal-Ion-Induced Wettability Transition.

Hydrophobic and oleophilic absorbent materials have received wide attention in recent years for potential applications in pollutant removal from accidental spills of oil or organic chemicals. In this work, we report a metal-ion-induced hydrophobic melamine sponge (MII-HMS) prepared by a one-step solution immersion process. The commercial melamine sponge (intrinsically superhydrophilic with a water contact angle of ∼0°) is immersed in an aqueous solution of transition metal ions (e.g., FeCl3, Fe(NO3)3, Zn(NO3)2, Ni(NO3)2, and Co(NO3)2) for a short period, followed by drying. This simple process renders the transition of the superhydrophilic melamine sponge to become highly hydrophobic (a water contact angle of ∼130°). Results from X-ray photoelectron spectroscopy and infrared spectroscopy suggest that the unprecedented transition is likely due to the formation of metal complexes during immersion. The MII-HMS is also oleophilic, exhibiting excellent oil absorption capabilities, ∼71-157 times of its weight, for a wide range of oils and organic solvents. Our work offers a simple, scalable, and economical approach to fabricate highly efficient absorbent materials for potential applications in oil spill recovery and environmental remediation.

Electrospinning preparation of a large surface area, hierarchically porous, and interconnected carbon nanofibrous network using polysulfone as a sacrificial polymer for high performance supercapacitors.

Carbon nanofibrous mats (CNFMs) are prepared by electrospinning of blended precursor of polyacrylonitrile and polysulfone (PSF) followed by pre-oxidation stabilization and carbonization. Addition of PSF as a sacrificial polymer leads to CNFMs with high surface area, large numbers of micropores and mesopores, good degree of carbonization, and interconnected fibrous network, due to the high decomposition temperature, release of SO2 during decomposition, and large amount of carbon residue of PSF during carbonization. The electrochemical characterization shows that the CNFM electrode has a specific capacitance of 272 F g-1 at a current density of 1 A g-1 with 74% of the specific capacitance retained at 50 A g-1 in 2.0 M KOH electrolyte. The CNFM electrodes have excellent cycling durability with 100% capacitance retention after 10 000 cycles.

Ultralight electrospun cellulose sponge with super-high capacity on absorption of organic compounds.

Three-dimensional, cost-effective, and renewable/recyclable absorbent materials with high capacities on absorption of organic compounds are urgently in demand. Herein, a facile while innovative approach is reported to develop ultralight electrospun cellulose sponge (UECS). The prepared UECS exhibits super-high absorption capacity (up to 232 times of its own weight) towards absorption of organic compounds due to high porosity (99.57%), low density (6.45mg/cm3), and hydrophobic surface feature (with water contact angle of 141.2°). Furthermore, the UECS is mechanically robust thus can be readily cut into different shapes; and it also possesses excellent stability against various organic compounds. Intriguingly, upon absorption of an organic compound, the shape-stable UECS organic gel can be formed. Hence, the developed UECS would be promising as environmental friendly absorbent on high-performance separation of organic compounds from aqueous systems; while the UECS organic gel could be utilized for the applications such as drug delivery and sensor.

Fluorescence Quenching of a Conjugated Polymer by Synergistic Amine-Carboxylic Acid and π-π Interactions for Selective Detection of Aromatic Amines in Aqueous Solution.

Fluorescence sensing of amine in aqueous solution is challenging. The various basicity and chemical structures of amines may lead to poor selectivity in aqueous solution, and selective fluorescence detection of primary aromatic amine is rarely reported. This paper presents design and synthesis of a fluorescent conjugated polymer for rapid and selective sensing of aromatic amines in aqueous solution. The fluorescent conjugated polymer, poly[fluorenyl-alt-p-phenyleneethynylene] with pendant carboxylic acid groups and long alky chains, is synthesized via palladium-catalyzed Sonogashira coupling reaction. The fluorescence of the polymer is selectively quenched by the aromatic amines in aqueous solution, whereas the aliphatic amines enhance the fluorescence of the polymer. The high selectivity to the aromatic amines, particularly to the environmentally important p-phenylenediamine, likely originates from the amplified π-π fluorescence quenching synergized by amine and carboxylic acid interaction. Our results demonstrate an effective material design strategy that may be extended to fluorescence sensing of other aromatic compounds.

Scalable and Facile Preparation of Highly Stretchable Electrospun PEDOT:PSS@PU Fibrous Nonwovens toward Wearable Conductive Textile Applications.

Flexible and stretchable conductive textiles are highly desired for potential applications in wearable electronics. This study demonstrates a scalable and facile preparation of all-organic nonwoven that is mechanically stretchable and electrically conductive. Polyurethane (PU) fibrous nonwoven is prepared via the electrospinning technique; in the following step, the electrospun PU nonwoven is dip-coated with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This simple method enables convenient preparation of PEDOT:PSS@PU nonwovens with initial sheet resistance in the range of 35-240 Ω/sq (i.e., the electrical conductivity in the range of 30-200 S m-1) by varying the number of dip-coating times. The resistance change of the PEDOT:PSS@PU nonwoven under stretch is investigated. The PEDOT:PSS@PU nonwoven is first stretched and then released repeatedly under certain strain (denoted as prestretching strain); the resistance of PEDOT:PSS@PU nonwoven becomes constant after the irreversible change for the first 10 stretch-release cycles. Thereafter, the resistance of the nonwoven does not vary appreciably under stretch as long as the strain is within the prestretching strain. Therefore, the PEDOT:PSS@PU nonwoven can be used as a stretchable conductor within the prestretching strain. Circuits using sheet and twisted yarn of the nonwovens as electric conductors are demonstrated.

A simple poly(3,4-ethylene dioxythiophene)/poly(styrene sulfonic acid) transistor for glucose sensing at neutral pH.

We demonstrate a simple transistor based on the conducting polymer poly(3,4-ethylene dioxythiophene)/poly(styrene sulfonic acid), capable of sensing glucose in a neutral pH buffer solution by a mechanism involving sensing of hydrogen peroxide.