Temperature sensitive nanogels for real-time imaging during transcatheter arterial embolization.

Several vascular embolization materials are commonly used in clinical practice, however, having application defects of varying degrees, such as poor intraoperative imaging and easy recanalization of embolized blood vessels, they are challenging for application during Transcatheter arterial embolization (TAE). Thus, an intraoperative visible vascular embolization material with good embolization effect and biocompatibility can improve transcatheter arterial embolization clinical efficacy to some extent. Our study aimed to synthesize a novel vascular embolization material that can achieve complete embolization of arterial trunks and peripheral vessels, namely poly (N-isopropyl acrylamide)-co-acrylic acid nanogel (NIPAM-co-AA). Iohexol 200 mg/mL was co-assembled with 7 wt% NIPAM-co-AA nanogel to create an intelligent thermosensitive radiopaque nanogel (INCA), which achieves a good intraoperative imaging effect and is convenient for transcatheter arterial bolus injection due to its good fluidity and temperature-sensitive sol-gel phase transition. The normal rabbit kidney embolism model further confirmed that INCA could effectively use Digital subtraction angiography (DSA) to achieve intraoperative imaging, and real-time monitoring of the embolization process could avoid mis-embolization and leakage. Meanwhile, in a 42-day study, INCA demonstrated an excellent embolization effect on the right renal artery of New Zealand white rabbits, with no vascular recanalization and ischemic necrosis and calcification remaining. As a result, this radiopaque thermosensitive nanogel has the potential to be an intelligent thermosensitive medical vascular embolization material, providing dual benefits in TAE intraoperative imaging and long-term postoperative embolization while effectively addressing the shortcomings and challenges of commonly used clinical vascular embolization agents.

Cellulose hydrogel-based biodegradable and recyclable magnetoelectric composites for electromechanical conversion.

Flexible electromechanical conversion devices have attracted enormous attention as energy harvesters and self-powered sensors in the fields of wearable electronics and robotics. However, current flexible devices composed of plastic polymers and metals suffer from non-degradability and limited recyclability. Herein, a biodegradable and recyclable hydrogel-based magnetoelectric (ME) composite is fabricated via introducing NdFeB magnetic particles and copper wires into the regenerated bacterial cellulose (rBC) hydrogel. The developed hydrogel-based ME composites can effectively convert the mechanical kinetic energy into electrical energy based on the principle of electromagnetic induction, which maximum voltage reaches 15 µV. In addition, degradation experiments are conducted in this work to demonstrate the hydrogel can be rapidly degraded within 3 h under the condition of enzyme and completely natural degraded within 49 days in water, respectively. Moreover, the left NdFeB particles and copper wires can be recyclable and reused for the same devices, leaving no environmentally hazardous electronic waste.

Biodegradable, Super-Strong, and Conductive Cellulose Macrofibers for Fabric-Based Triboelectric Nanogenerator.

Electronic fibers used to fabricate wearable triboelectric nanogenerator (TENG) for harvesting human mechanical energy have been extensively explored. However, little attention is paid to their mutual advantages of environmental friendliness, mechanical properties, and stability. Here, we report a super-strong, biodegradable, and washable cellulose-based conductive macrofibers, which is prepared by wet-stretching and wet-twisting bacterial cellulose hydrogel incorporated with carbon nanotubes and polypyrrole. The cellulose-based conductive macrofibers possess high tensile strength of 449 MPa (able to lift 2 kg weights), good electrical conductivity (~ 5.32 S cm-1), and excellent stability (Tensile strength and conductivity only decrease by 6.7% and 8.1% after immersing in water for 1 day). The degradation experiment demonstrates macrofibers can be degraded within 108 h in the cellulase solution. The designed fabric-based TENG from the cellulose-base conductive macrofibers shows a maximum open-circuit voltage of 170 V, short-circuit current of 0.8 µA, and output power at 352 µW, which is capable of powering the commercial electronics by charging the capacitors. More importantly, the fabric-based TENGs can be attached to the human body and work as self-powered sensors to effectively monitor human motions. This study suggests the potential of biodegradable, super-strong, and washable conductive cellulose-based fiber for designing eco-friendly fabric-based TENG for energy harvesting and biomechanical monitoring.

A Biodegradable and Recyclable Piezoelectric Sensor Based on a Molecular Ferroelectric Embedded in a Bacterial Cellulose Hydrogel.

Currently, various electronic devices make our life more and more safe, healthy, and comfortable, but at the same time, they produce a large amount of nondegradable and nonrecyclable electronic waste that threatens our environment. In this work, we explore an environmentally friendly and flexible mechanical sensor that is biodegradable and recyclable. The sensor consists of a bacterial cellulose (BC) hydrogel as the matrix and imidazolium perchlorate (ImClO4) molecular ferroelectric as the functional element, the hybrid of which possesses a high sensitivity of 4 mV kPa-1 and a wide operational range from 0.2 to 31.25 kPa, outperforming those of most devices based on conventional functional biomaterials. Moreover, the BC hydrogel can be fully degraded into glucose and oligosaccharides, while ImClO4 can be recyclable and reused for the same devices, leaving no environmentally hazardous electronic waste.

Programmable Anisotropic Hydrogel Composites for Soft Bioelectronics.

Fabrication of hydrogel composites embedded with aligned 1D nanoparticles has shown substantial growth over the past 5 years. Direct ink printing technology (DIW) has been used in this work to create the alignment of the 1D nanoparticles due to the shear gradient of the pseudoplastic precursor (2-hydroxyethyl methacrylate (HEMA) with thickening agents). Orderly distributed 1D particles constructing anisotropic nanostructures endow the hydrogel composite with unique mechanical, electric, or electromechanical coupling properties. Quasi-static uniaxial tensile test, electric resistivity, and piezoresistivity measurements have been conducted for investigating the mechanical, electric, and electromechanical coupling properties of the hydrogel composites, respectively. Based on the experimental results, it can be speculated that the developed printing process is able to fabricate hydrogel composites with programmable anisotropic mechanical, electric, and electromechanical properties. The products pumped out from this work have the potential of being substrates for soft devices and may have a great impact on the fields of flexible bioelectronics.

Solution-Processable Conductive Composite Hydrogels with Multiple Synergetic Networks toward Wearable Pressure/Strain Sensors.

A biocompatible, flexible, yet robust conductive composite hydrogel (CCH) for wearable pressure/strain sensors has been achieved by an all-solution-based approach. The CCH is rationally constructed by in situ polymerization of aniline (An) monomers in the polyvinyl alcohol (PVA) matrix, followed by the cross-linking of PVA with glutaraldehyde (GA) as the cross-linker. The unique multiple synergetic networks in the CCH including strong chemical covalent bonds and abundance of weak physical cross-links, i.e., hydrogen bondings and electrostatic interactions, impart excellent mechanical strength (a fracture tensile strength of 1200 kPa), superior compressibility (ε = 80%@400 kPa), outstanding stretchability (a fracture strain of 670%), high sensitivity (0.62 kPa-1 at a pressure range of 0-1.0 kPa for pressure sensing and a gauge factor of 3.4 at a strain range of 0-300% for strain sensing, respectively), and prominent fatigue resistance (1500 cycling). As the flexible wearable sensor, the CCH is able to monitor different types of human motion and diagnostically distinguish speaking. As a proof of concept, a sensing device has been designed for the real-time detection of 2D distribution of weight or pressure, suggesting its promising potentials for electronic skin, human-machine interaction, and soft robot applications.

Manipulating multipole resonances in spoof localized surface plasmons for wideband filtering.

The spoof localized surface plasmon (LSP) has been widely investigated but mostly with fixed multipole resonances. This Letter proposes a method to generate multipole resonances by adding a slit on the metallic ring of a complementary LSP. This slit theoretically introduces two new boundary conditions and new modes. To validate this approach, complementary LSPs with and without slits at three different angular positions are theoretically analyzed and numerically simulated. To validate and demonstrate the potential application of the proposed LSP structure, a bandpass filter (BPF) in a single-layer substrate is designed and measured by exciting the LSP with a slit on the metallic ring. The measured results show that by simply adding a slit, the BPF achieves a fractional bandwidth of 42.7% (2.5 GHz), for both |S11|<-10dB and |S21| within 1 dB variation. In the passband, a flat group delay between 0.57 ns and 0.75 ns is obtained. Moreover, the proposed structure features a low profile and a compact radius of 0.136 wavelength. By dynamically controlling slit/slits with varactors or diodes, the proposed structure is theoretically promising to be reconfigurable at microwave and even terahertz frequencies.

Biodegradable and Electroactive Regenerated Bacterial Cellulose/MXene (Ti3 C2 Tx ) Composite Hydrogel as Wound Dressing for Accelerating Skin Wound Healing under Electrical Stimulation.

Traditional wound dressings mainly participate in the passive healing processes and are rarely engaged in active wound healing by stimulating skin cell behaviors. Electrical stimulation (ES) has been known to regulate skin cell behaviors. Herein, a series of multifunctional hydrogels based on regenerated bacterial cellulose (rBC) and MXene (Ti3 C2 Tx ) are first developed that can electrically modulate cell behaviors for active skin wound healing under external ES. The composite hydrogel with 2 wt% MXene (rBC/MXene-2%) exhibits the highest electrical conductivity and the best biocompatibility. Meanwhile, the rBC/MXene-2% hydrogel presents desired mechanical properties, favorable flexibility, good biodegradability, and high water-uptake capacity. An in vivo study using a rat full-thickness defect model reveals that this rBC/MXene hydrogel exhibits a better therapeutic effect than the commercial Tegaderm film. More importantly, in vitro and in vivo data demonstrate that coupling with ES, the hydrogel can significantly enhance the proliferation activity of NIH3T3 cells and accelerate the wound healing process, as compared to non-ES controls. This study suggests that the biodegradable and electroactive rBC/MXene hydrogel is an appealing candidate as a wound dressing for skin wound healing, while also providing an effective synergistic therapeutic strategy for accelerating wound repair process through coupling ES with the hydrogel dressing.

Enhanced cell proliferation by electrical stimulation based on electroactive regenerated bacterial cellulose hydrogels.

Electric fields (EFs) have shown promising impact on wound healing, these alone are ineffective to stimulate the whole wound area. In this study, we developed a newly regenerated bacterial cellulose/polypyrrole/carbon nanotube (rBC/PPy/CNT) electroactive hydrogel through cellulose dissolution, and physical and chemical crosslinking method to enhance cell proliferation with EF for wound healing. The hydrogels were characterized with FESEM, FTIR, XRD, TGA, conductivity, mechanical, and swelling tests. The results showed that PPy and CNTs were successfully deposited in the rBC/PPy/CNT hydrogels, which exhibited excellent thermal stability, mechanical strength, recoverability, swelling ability, and demonstra-ted 107 fold higher electrical conductivity than rBC. In vitro analysis proved good biocompatibility of rBC/PPy/CNT whereon NIH3T3 cells proliferated evidently. Especially, the combination of EF with rBC/PPy/CNT significantly enhanced the cell proliferation as compared to rBC (p < 0.05). The overall results suggest the promising potential of rBC/PPy/CNT combined with EF for enhancing cellular activities in wound healing.

Superhydrophobic Liquid-Solid Contact Triboelectric Nanogenerator as a Droplet Sensor for Biomedical Applications.

Superhydrophobic surfaces repel water and other liquids such as tissue fluid, blood, urine, and pus, which can open up a new avenue for the development of biomedical devices and has led to promising advances across diverse fields, including plasma separator devices, blood-repellent sensors, vascular stents, and heart valves. Here, the fabrication of superhydrophobic liquid-solid contact triboelectric nanogenerators (TENGs) and their biomedical applications as droplet sensors are reported. Triboelectrification energy can be captured and released when droplets are colliding or slipping on the superhydrophobic layer. The developed superhydrophobic TENG possesses multiple advantages in terms of simple fabrication, bendability, self-cleaning, self-adhesiveness, high sensitivity, and repellency to not only water but also a variety of solutions, including blood with a contact angle of 158.6°. As a self-powered sensor, the developed prototypes of a drainage bottle droplet sensor and a smart intravenous injection monitor based on the superhydrophobic liquid-solid contact TENG can monitor the clinical drainage operation and intravenous infusion in real time, respectively. These prototypes suggest the potential merit of this superhydrophobic liquid-solid contact TENG in clinical application, paving the way for accurately monitoring clinical drainage operations and intravenous injection or blood transfusion in the future.

Shaping Bessel beams using source-integrated folded reflectarray.

This Letter proposes a highly integrated reflection-type approach to generate non-diffracting Bessel beams using a source-integrated folded reflectarray antenna (FRA). The FRA not only transforms spherical waves radiated by the feeding source to conical waves but also directly produces Bessel beams by specifying the phase distribution of reflectarray elements. To validate this approach, a millimeter-wave zero-order Bessel beam generator and a conventional collimated beam structure are analyzed, designed, fabricated, and measured. Good agreement among theoretical analysis, full-wave simulation, and experimental results demonstrate that the proposed FRA successfully generates non-diffracting Bessel beams and, moreover, the reflectarray elements are fully integrated with the feeding source in the same low-cost single-layered printed circuit board.

Beam Steering Using Momentum-Reconfigurable Goubau Meta-Line Radiators.

Spoof/designer surface plasmon polaritons (SPP) and Goubau line belong to the same category of single-conductor surface waveguide. They feature easy integration and high field confinement capability, and hence are good candidates for wave guiding and radiating at terahertz frequencies. Here, we propose a momentum-reconfigurable Goubau meta-line radiator that is capable of digitally steering its beam at a fixed frequency, in contrast to conventional SPP or Goubau line radiators relying on changing frequencies to steer beams. By periodically loading switchable meta-lines with ON and OFF states along the Goubau line, the modulation period and hence the momentum of Goubau line radiators can be dynamically controlled. The proposed Goubau line radiator is able to steer the main beam at a given frequency by independently switching ON or OFF each unit cell. As a proof of concept, we use line connection and disconnection to mimic ON and OFF state of the switch, respectively. Several radiators, representing different switching coding combinations, are fabricated and experimentally validated. Although this momentum-reconfigurable Goubau meta-line radiator is demonstrated at microwave frequency, it can be easily extended to terahertz frequencies.

Continuous Beam Steering Through Broadside Using Asymmetrically Modulated Goubau Line Leaky-Wave Antennas.

Goubau line is a single-conductor transmission line, featuring easy integration and low-loss transmission properties. Here, we propose a periodic leaky-wave antenna (LWA) based on planar Goubau transmission line on a thin dielectric substrate. The leaky-wave radiations are generated by introducing periodic modulations along the Goubau line. In this way, the surface wave, which is slow-wave mode supported by the Goubau line, achieves an additional momentum and hence enters the fast-wave region for radiations. By employing the periodic modulations, the proposed Goubau line LWAs are able to continuously steer the main beam from backward to forward within the operational frequency range. However, the LWAs usually suffer from a low radiation efficiency at the broadside direction. To overcome this drawback, we explore both transversally and longitudinally asymmetrical modulations to the Goubau line. Theoretical analysis, numerical simulations and experimental results are given in comparison with the symmetrical LWAs. It is demonstrated that the asymmetrical modulations significantly improve the radiation efficiency of LWAs at the broadside. Furthermore, the measurement results agree well with the numerical ones, which experimentally validates the proposed LWA structures. These novel Goubau line LWAs, experimentally demonstrated and validated at microwave frequencies, show also great potential for millimeter-wave and terahertz systems.