Insecticidal Activity and Insecticidal Mechanism of Total Saponins from Camellia oleifera.

Chemical pesticides are commonly used during the cultivation of agricultural products to control pests and diseases. Excessive use of traditional pesticides can cause environmental and human health risks. There are ongoing searches for new plant-derived pesticides to reduce the use of chemical pesticides. In this study, tea saponin extracts of different purities were extracted from Camellia oleifera seeds using AB-8 macroporous resin and gradient elution with ethanol. The insecticidal effects of the tea saponin extracts were evaluated by contact toxicity tests and stomach toxicity tests using the lepidopteran pest of tea plantation, Ectropis obliqua. The total saponins extracted using 70% ethanol showed strong contact toxicity (LC50 = 8.459 mg/L) and stomach toxicity (LC50 = 22.395 mg/L). In-depth mechanistic studies demonstrated that tea saponins can disrupt the waxy layer of the epidermis, causing serious loss of water, and can penetrate the inside of the intestine of E. obliqua. After consumption of the tea saponins, the intestinal villi were shortened and the cavities of the intestinal wall were disrupted, which resulted in larval death. This study highlights the potential of tea saponins as a natural, plant-derived pesticide for the management of plant pests.

Integrated Fibrous Iontronic Pressure Sensors with High Sensitivity and Reliability for Human Plantar Pressure and Gait Analysis.

Flexible sensing systems (FSSs) designed to measure plantar pressure can deliver instantaneous feedback on human movement and posture. This feedback is crucial not only for preventing and controlling diseases associated with abnormal plantar pressures but also for optimizing athletes' postures to minimize injuries. The development of an optimal plantar pressure sensor hinges on key metrics such as a wide sensing range, high sensitivity, and long-term stability. However, the effectiveness of current flexible sensors is impeded by numerous challenges, including limitations in structural deformability, mechanical incompatibility between multifunctional layers, and instability under complex stress conditions. Addressing these limitations, we have engineered an integrated pressure sensing system with high sensitivity and reliability for human plantar pressure and gait analysis. It features a high-modulus, porous laminated ionic fiber structure with robust self-bonded interfaces, utilizing a unified polyimide material system. This system showcases a high sensitivity (156.6 kPa-1), an extensive sensing range (up to 4000 kPa), and augmented interfacial toughness and durability (over 150,000 cycles). Additionally, our FSS is capable of real-time monitoring of plantar pressure distribution across various sports activities. Leveraging deep learning, the flexible sensing system achieves a high-precision, intelligent recognition of different plantar types with a 99.8% accuracy rate. This approach provides a strategic advancement in the field of flexible pressure sensors, ensuring prolonged stability and accuracy even amidst complex pressure dynamics and providing a feasible solution for long-term gait monitoring and analysis.

New Soft Actuating Way by Rapidly Temperature Change of Electrocaloric Effect.

Compared to traditional temperature control methods, the electrocaloric (EC) effect offers several advantages such as small size, rapid response, and environmental friendliness. However, current EC effects are generally used for the cooling area rather than heating. Here, poly(vinylidenefluorideter-trifluoroethylene-ter-chlorofluoroethylene) [P(VDF-TrFE-CFE)] film is combined with an electrothermal actuator (ETA) composed of polyethylene (PE) film and carbon nanotube (CNT) film. The heating and cooling process of the EC effect is used to help drive the ETA. The P(VDF-TrFE-CFE) film can produce a temperature change (ΔT) of 3.7 °C at 90 MV/m, and this process occurs within 0.1 s. With this ΔT, the composite film actuator can produce a deflection of 10°. In addition, due to the electrostrictive effect of P(VDF-TrFE-CFE), the composite film can also be used as an actuator. At 90 MV/m, the composite film actuator can produce a deflection over 240° within 0.05 s. Apart from other current driving modes for thermally responsive actuators, in this paper, a new type of soft actuating composite film by the temperature change of the EC effect is proposed. Except from ETAs, the EC effect can also have a wide application prospect in other thermally responsive actuators, including shape memory polymer actuators, shape memory alloy actuators, and so on.

Mechanically Reinforced Rigid Polyimide Foam via Chemically Grafting Isocyanate Acid for Ultrabroad Band Microwave Absorption.

Polyimide (PI) foam with excellent microwave absorption (MA) performance and desirable compressive strength is highly critical and in demand in the structural MA components. Although the satisfactory MA performance of the present PI-based MA foams has been achieved by employing diverse methods, the relatively low compressive strength (∼KPa) restricted them from use as structural MA foams in practical application. Herein, isocyanate acid was introduced to the backbone of PI resin, which not only increased the PI backbone polarity and strength as rigid chain segment, but also served as a self-foaming component. The porous structure of PI foams was readily regulated by adjusting the water and carbon nanotube (CNT) filler contents of precursor dispersion. As a result of the improved polarity of the PI backbone resulted from the isocyanate group and high dielectric loss of CNT, the high compressive strength of 7.04 MPa and impressive MA property of the resultant PI foam with a low CNT loading ratio of 1.5 wt % were achieved, which were much higher than those reported previously. Especially, the effective absorption bandwidth (EAB) (RL < -10 dB) was up to 10.7 GHz (at the thickness of 3 mm), covering the C, X, and Ku bands simultaneously. Meanwhile, the EAB of the as-prepared PI foam retained 9.3 and 9.7 GHz even after being subjected to liquid nitrogen (-196 °C) and high temperature (300 °C) treatments due to the desirable stability of PI. In addition, the excellent thermal insulation resulted from the pores structure and low filler content was achieved, where the top surface only presented 60 °C after placing on 300 °C platform for 30 min. The high compressive strength, impressive MA property, and thermal insulation endowed the resultant CNT/PI foam with great potential application as structural MA foam in a harsh service environment.

Polyvinylpyrrolidone induced uniform coating of nickel nanoparticles on carbon nanotubes for efficient microwave absorption.

The impedance matching performance of carbon nanotubes (CNTs) can be effectively enhanced by developing a uniform magnetic impedance matching layer, which can take on critical significance in achieving the desirable microwave absorption (MA) performance. To obtain a uniform coating of Nickel (Ni) nanoparticles on CNTs, several methods have been developed (e.g., the γ-irradiation technique, electroless deposition, as well as microwave welding method). However, the intricate and complicated conditions of the above-mentioned methods limit their wide application. Therefore, controlling the distribution of Ni nanoparticles with the aid of a concise and effective method remains a great challenge. Herein, in view of the uniform dispersion effect of polyvinylpyrrolidone (PVP) on CNTs and its complexation with Ni ions, uniform coating of Ni nanoparticles on CNTs is well developed after it is introduced in the hydrothermal process. The prepared Ni/CNTs composites exhibited excellent MA performance in comparison with those of reported Ni/CNTs composites for the ideal impedance matching performance and microwave attenuation ability. When the filler content was only 15 wt%, the minimum reflection loss (RLmin) reached -39.5 dB, and the effective bandwidth (EB) with RL < -10 dB reached 5.2 GHz at the thickness of 1.15 mm. A scalable strategy of regulating the distribution of Ni nanoparticles and preparing a lightweight microwave absorber based on CNTs was developed in this study, which can serve as a vital guideline for preparing novel MA composite materials.