Ultrasound-Driven Injectable and Fully Biodegradable Triboelectric Nanogenerators.

Implantable medical devices (IMDs) provide practical approaches to monitor physiological parameters, diagnose diseases, and aid treatment. However, device installation, maintenance, and long-term implantation increase the risk of infection with conventional IMDs. Therefore, medical devices with biocompatibility, controllability, and miniaturization are highly demandable. An ultrasound-driven, biodegradable, and injectable triboelectric nanogenerator (I-TENG) is demonstrated to reduce the risks of implant-related injuries and infections. The injection can be given by subcutaneous injection with a needle to minimize the implantation incision. The stable output of I-TENG is driven by ultrasound (20 kHz, 1 W cm-2 ), with a voltage of 356.8 mV and current of 1.02 µA during in vivo studies and an electric field of about 0.92 V mm-1 during ex vivo experiments. The cell scratch and proliferation assays showed that the delivered electric field effectively increased cell migration and proliferation, indicating a significant potential to accelerate healing with electricity.

An Ultrasound-Driven Bioadhesive Triboelectric Nanogenerator for Instant Wound Sealing and Electrically Accelerated Healing in Emergencies.

A bioadhesive triboelectric nanogenerator (BA-TENG), as a first-aid rescue for instant and robust wound sealing and ultrasound-driven accelerated wound healing, is designed. This BA-TENG is fabricated with biocompatible materials, and integrates a flexible TENG as the top layer and bioadhesive as the bottom layer, resulting in effective electricity supply and strong sutureless sealing capability on wet tissues. When driven by ultrasound, the BA-TENG can produce a stable voltage of 1.50 V and current of 24.20 µA underwater. The ex vivo porcine colon organ models show that the BA-TENG seals defects instantly (≈5 s) with high interfacial toughness (≈150 J m-2 ), while the rat bleeding liver incision model confirms that the BA-TENG performs rapid wound closure and hemostasis, reducing the blood loss by about 82%. When applied in living rats, the BA-TENG not only seals skin injuries immediately but also produces a strong electric field (E-field) of about 0.86 kV m-1 stimulated by ultrasound to accelerate skin wound healing significantly. The in vitro studies confirm that these effects are attributed to the E-field-accelerated cell migration and proliferation. In addition, these TENG adhesives can be applied to not only wound treatment, nerve stimulation and regeneration, and charging batteries in implanted devices.

Analysis of Defect Recovery in Reduced Graphene Oxide and Its Application as a Heater for Self-Healing Polymers.

Reduced graphene oxide (RGO) obtained from graphene oxide has received much attention because of its simple and cost-effective manufacturing process. Previous studies have demonstrated the scalable production of RGO with relatively high quality; however, irreducible defects on RGO deteriorate the unique intrinsic physical properties of graphene, such as high-mobility electrical charge transport, limiting its potential applicability. Using the enhanced chemical reactivity of such defects, atomic layer deposition (ALD) can be a useful method to selectively passivate the defect sites. Herein, we analyzed the selective formation of Pt by ALD on the defect sites of RGO and investigated the effect of Pt formation on the electrical properties of RGO by using ultrafast terahertz (THz) laser spectroscopy. Time-resolved THz measurements directly corroborated that the degree of the defect-recovering property of ALD Pt-treated RGO appearing as Auger-type sub-picosecond relaxation, which is otherwise absent in pristine RGO. In addition, the conductivity improvement of Pt-recovered RGO was theoretically explained by density functional theory calculations. The ALD Pt-passivated RGO yielded a superior platform for the fabrication of a highly conductive and transparent graphene heater. By using the ALD Pt/RGO heater embedded underneath scratched self-healing polymer materials, we also demonstrated the effective recovery property of self-healing polymers with high-performance heating capability. Our work is expected to result in significant advances toward practical applications for RGO-based flexible and transparent electronics.

Tunable Out-of-Plane Piezoelectricity in Thin-Layered MoTe2 by Surface Corrugation-Mediated Flexoelectricity.

Piezoelectricity crystallographically exists only in the in-plane direction in two-dimensional transition metal dichalcogenides. Here, we demonstrated flexoelectricity-tunable out-of-plane piezoelectricity in semiconducting 2H-MoTe2 flakes by creating surface corrugation. In particular, the strong out-of-plane piezoelectricity and its spatial variation depending on local flexoelectricity was observed even though crystallographically there exists only in-plane piezoelectricity. Surface corrugation-mediated flexoelectricity tuning can be applied to other two-dimensional or thin-layered materials and, furthermore, the results could provide useful information on the interweaving nature between mechanical stimulus and electric dipole in low-dimensional materials.

Atomic Observation of Filling Vacancies in Monolayer Transition Metal Sulfides by Chemically Sourced Sulfur Atoms.

Chemical treatment using bis(trifluoromethane) sulfonimide (TFSI) was shown to be particularly effective for increasing the photoluminescence (PL) of monolayer (1L) MoS2, suggesting a convenient method for overcoming the intrinsically low quantum yield of this material. However, the underlying atomic mechanism of the PL enhancement has remained elusive. Here, we report the microscopic origin of the defect healing observed in TFSI-treated 1L-MoS2 through a correlative combination of optical characterization and atomic-scale scanning transmission electron microscopy, which showed that most of the sulfur vacancies were directly repaired by the extrinsic sulfur atoms produced from the dissociation of TFSI, concurrently resulting in a significant PL enhancement. Density functional theory calculations confirmed that the reactive sulfur dioxide molecules that dissociated from TFSI can be reduced to sulfur and oxygen gas at the vacancy site to form strongly bound S-Mo. Our results reveal how defect-mediated nonradiative recombination can be effectively eliminated by a simple chemical treatment method, thereby advancing the practical applications of monolayer semiconductors.