Anisotropic Liesegang pattern for the nonlinear elastic biomineral-hydrogel complex.

The Liesegang pattern is a beautiful natural anisotropic patterning phenomenon observed in rocks and sandstones. This study reveals that the Liesegang pattern can induce nonlinear elasticity. Here, a Liesegang-patterned complex with biomineral-hydrogel repetitive layers is prepared. This Liesegang-patterned complex is obtained only when the biomineralization is performed under the supersaturated conditions. The Liesegang-patterned complex features a nonlinear elastic response, whereas a complex with a single biomineral shell shows a linear behavior, thus demonstrating that the Liesegang pattern is essential in achieving nonlinear elasticity. The stiff biomineral layers have buffered the concentrated energy on behalf of soft hydrogels, thereby exposing the hydrogel components to reduced stress and, in turn, enabling them to perform the elasticity continuously. Moreover, the nonlinear elastic Liesegang-patterned complex exhibits excellent stress relaxation to the external loading, which is the biomechanical characteristic of cartilage. This stress relaxation allows the bundle of fiber-type Liesegang-patterned complex to endure greater deformation.

Recycled, Contaminated, Crumpled Aluminum Foil-Driven Triboelectric Nanogenerator.

With rapid urbanization and global population growth, the amount of wasted aluminum foil is significantly increasing. Most deformed and contaminated foil is difficult to recycle; hence, it is landfilled or incinerated, causing environmental pollution. Therefore, using aluminum foil waste for electricity may be conducive to addressing environmental problems. In this regard, various literatures have explored the concept of energy generation using foil, while a crumple ball design for this purpose has not been studied. Thus, a recycled foil-based crumpled ball triboelectric nanogenerator (RFCB-TENG) is proposed. The crumpled ball design can minimize the effects of contamination on foil, ensuring efficient power output. Moreover, owing to novel crumpled design, the RFCB-TENG has some outstanding characteristics to become a sustainable power source, such as ultralight weight, low noise, and high durability. By introducing the air-breakdown model, the RFCB-TENG achieved an output peak voltage of 648 V, a current of 8.1 mA cm3 , and an optimum power of 162.7 mW cm3 . The structure of the RFCB-TENG is systemically optimized depending on the design parameters to realize the optimum output performance. Finally, the RFCB-TENG operated 500 LEDs and 30-W commercial lamps. This work paves the guideline for effectively fabricating the TENG using waste-materials while exhibiting outstanding characteristics.

Lightweight mobile stick-type water-based triboelectric nanogenerator with amplified current for portable safety devices.

Due to its abundance, mechanical energy is a promising ambient energy source. Triboelectric nanogenerators (TENGs) represent an effective mechanical energy harvesting method based on the use of contact electrification. The existing liquid-based TENGs can operate robustly without surface damage; however, the output of these TENGs is considerably smaller than that of solid-based TENGs. Notably, liquid-based TENGs in which the liquid directly contacts the conductive material can produce an electrical current of more than few mA. However, the liquid reservoir must have an adequate volume, and sufficient space must be provided for the liquid to move for generating the electrical output. To ensure a compact and lightweight design and produce electrical output in the low input frequency range, we introduce a mobile stick-type water-based TENG (MSW-TENG). The proposed MSW-TENG can generate an open-circuit voltage and closed-circuit current of up to 710 V and 2.9 mA, respectively, and be utilized as self-powered safety device. The findings of this study can promote the implementation of TENGs in everyday applications.

Stress Dissipation Encoded Silk Fibroin Electrode for the Athlete-Beneficial Silk Bioelectronics.

The kinetic body motions have guided the core-shell fabrics of wearable bioelectronics to be elastoplastic. However, the polymeric electrodes follow the trade-off relationship between toughness and stretchability. To this end, the stress dissipation encoded silk fibroin electrode is proposed as the core electrode of wearable bioelectronics. Significantly, the high degree of intrinsic stress dissipation is realized via an amino acid crosslink. The canonical phenolic amino acid (i.e., tyrosine) of silk fibroin is engineered to bridge the secondary structures. A sufficient crosslink network is constructed when tyrosine is exposed near the amorphous strand. The stress dissipative tyrosine crosslink affords 12.5-fold increments of toughness (4.72 to 58.9 MJ m-3 ) and implements the elastoplastic silk fibroin. The harmony of elastoplastic core electrodes with shell fabrics enables the wearable bioelectronics to employ mechanical performance (elastoplasticity of 750 MJ m-3 ) and stable electrical response. The proposed wearable is capable of assisting the effective workouts via triboelectricity. In principle, active mobility with suggested wearables potentially relieves muscular fatigues and severe injuries during daily fitness.

A portable device for water-sloshing-based electricity generation based on charge separation and accumulation.

Hydropower generation is a well-known electricity generation technique that uses Faraday's law and hydraulic turbines. Recently, a triboelectrification-based electricity generation device, using water as the triboelectric material (W-TEG) was developed. In addition to the enhancement of the electrical output performance through the operation mechanism, the characteristics of the W-TEG must be examined at the design level to facilitate its portable application. Therefore, in this work, we developed a portable water-sloshing-based electricity generator (PS-EG) that can produce a high electric output and achieved its closed-loop circuit design and quantitative analysis for portable applications. The proposed PS-EG produced peak open-circuit voltage (V OC ) and closed-circuit current (I CC ) of up to 484 V and 4.1 mA, respectively, when subjected to vibrations of 2 Hz. The proposed PS-EG can be effectively used as an auxiliary power source for small electronics and sensors.

Fabrication of Graphene Based Durable Intelligent Personal Protective Clothing for Conventional and Non-Conventional Chemical Threats.

Conventional or non-conventional chemical threat is gaining huge attention due to its unpredictable and mass destructive effects. Typical military protective suits have drawbacks such as high weight, bulky structure, and unpredictable lifetime. A durable, light, and scalable graphene e-fabric was fabricated from CVD-grown graphene by a simple co-lamination method. The sheet resistance was below 1 kΩ/sq over the wide surface area even after 1000 bending cycles. A graphene triboelectric nanogenerator showed the peak VOC of 68 V and the peak ICC of 14.4 µA and 1 µF capacitor was charged successfully in less than 1 s. A wearable chemical sensor was also fabricated and showed a sensitivity up to 53% for nerve chemical warfare agents (GD). DFT calculations were conducted to unveil the fundamental mechanisms underlying the graphene e-fabric sensor. Additionally, protection against chemical warfare agents was tested, and a design concept of graphene-based intelligent protective clothing has been proposed.

Versatile surface for solid-solid/liquid-solid triboelectric nanogenerator based on fluorocarbon liquid infused surfaces.

The triboelectric nanogenerator (TENG) is a recent mechanical energy harvesting technology that has been attracting significant attention. Its working principle involves the combination of triboelectrification and electrostatic induction. The TENG can harvest electrical energy from both solid-solid and liquid-solid contact TENGs. Due to their physical difference, triboelectric materials in the solid-solid TENG need to have high mechanical properties and the surface of the liquid-solid contact TENG should repel water. Therefore, the surface of the TENG must be versatile for applications in both solid-solid and liquid-solid contact environments. In this work, we develop a solid-solid/liquid-solid convertible TENG that has a slippery liquid-infused porous surface (SLIPS) at the top of the electrode. The SLIPS consists of a HDFS coated hierarchical Al(OH)3 structure and fluorocarbon liquid. The convertible TENG developed in this study is capable of harvesting electricity from both solid-solid and liquid-solid contacts due to the high mechanical property of Al(OH)3 and the water-based liquid repelling nature of the SLIPS. When the contact occurs in freestanding mode, electrical output was generated through solid-solid/liquid-solid sliding motions. The convertible TENG can harvest electricity from both solid-solid and liquid-solid contacts; thus, it can be a unified solution for TENG surface fabrication.

Superhydrophobic Water-Solid Contact Triboelectric Generator by Simple Spray-On Fabrication Method.

Energy harvesting is a method of converting energy from ambient environment into useful electrical energy. Due to the increasing number of sensors and personal electronics, energy harvesting technologies from various sources are gaining attention. Among energy-harvesting technologies, triboelectric nanogenerator (TENG) was introduced as a device that can effectively generate electricity from mechanical motions by contact-electrification. Particularly, liquid-solid contact TENGs, which use the liquid itself as a triboelectric material, can overcome the inevitable friction wear between two solid materials. Using a commercial aerosol hydrophobic spray, liquid-solid contact TENGs, with a superhydrophobic surface (contact angle over 160°) can be easily fabricated with only a few coating processes. To optimize the fabrication process, the open-circuit voltage of sprayed superhydrophobic surfaces was measured depending on the number of coating processes. To demonstrate the simple fabrication and applicability of this technique on random 3D surfaces, a liquid-solid contact TENG was fabricated on the brim of a cap (its complicated surface structure is due to the knitted strings). This simple sprayed-on superhydrophobic surface can be a possible solution for liquid-solid contact TENGs to be mass produced and commercialized in the future.