Visible light is an easily achievable and mild trigger for self-healing materials. By incorporating dynamic diselenide bonds into polyurethane, visible-light-induced self-healing materials can be fabricated. Besides mild visible light, the healing process can also be realized using directional laser irradiation, which makes the system a remotely controllable self-healing system.
Dynamic covalent bonds are extensively employed in dynamic combinatorial chemistry. The metathesis reaction of disulfide bonds is widely used, but requires catalysis or irradiation with ultraviolet (UV) light. It was found that diselenide bonds are dynamic covalent bonds and undergo dynamic exchange reactions under mild conditions for diselenide metathesis. This reaction is induced by irradiation with visible light and stops in the dark. The exchange is assumed to proceed through a radical mechanism, and experiments with 2,2,6,6-tetramethylpiperidin-1-yloxyl (TEMPO) support this assumption. Furthermore, the reaction can be conducted in different solvents, including protic solvents. Diselenide metathesis can also be used to synthesize diselenide-containing asymmetric block copolymers. This work thus entails the use of diselenide bonds as dynamic covalent bonds, the development of a dynamic exchange reaction under mild conditions, and an extension of selenium-related dynamic chemistry.
Preparation of Au/PDMS films: PDMS films were prepared from Sylgard 184 Silicone Elastomer Kit (Dow Inc.). A mixture of precursor and crosslinker at 10:1 ratio was spin coated on a fluorinated silicon wafer at 800 rpm for 60 s, and cured 60 o C for 5 h. The prepared PDMS films were around 70 μm thick. Au nanolayers were deposited by a vacuum thermal evaporator (Nano 36, Kurt J. Lesker) under 2×10 -6 Torr with a deposition rate of 0.3 Å/s. The Au source was purchased from Kurt J. Lesker and the purity was 99.99%. The deposition time was controlled to get 80 nm thick gold layers.Synthesis of dopamine methacrylamide (DMA) monomer: DMA monomer was synthesized according to the previously reported method. [S1] 10 g of sodium tetraborate and 4 g of sodium bicarbonate were dissolved in 100 mL deionized water and bubbled with nitrogen for 20 min.With continuous nitrogen flow, 5 g of dopamine hydrochloride (26.4 mmol) was dissolved in the solution. Then 5 mL of methacrylate anhydride (94 % purity, 29.1 mmol) in 20 ml THF was added dropwise, during this process the pH was kept above 8 with the addition of 1 M sodium hydroxide. The mixture was stirred overnight at room temperature. The reaction mixture was washed twice with 50 mL ethyl acetate, and then the pH of the aqueous solution was changed to less than 2 and extracted with 50 mL of ethyl acetate three times. The ethyl acetate layers were combined and dried over sodium sulfate, evaporated to reduce to around 30
Noninvasive on-skin electrodes record the electrical potential changes from human skin, which reflect body condition and are applied for healthcare, sports management, and modern lifestyle. However, current on-skin electrodes have poor conformal properties under sweaty condition in real-life because of decreased electrode-skin adhesion with sweat film at the interface. Here, we fabricated biocomposite electrodes based on silk fibroin (SF) through interfacial polymerization, which is applicable on sweaty skin. Interfacial polymerized conductive polypyrrole (PPy) and SF are structurally interlocked and endow the whole electrode with uniform stretchability. Existence of water results in similar Young's modulus of SF to the skin and enhanced interfacial adhesion. It keeps the electrodes conformal to skin under sweaty condition and allows reliable collection of ambulatory electrophysiological signals during sports and sweating. Wearable devices with these electrodes were used to acquire continuous and stable real-time electrocardiography (ECG) signals during running for 2 h. The collected signals can provide information for sports management and are also analyzed by artificial intelligence to show their potential for intelligent human emotion monitoring. Our strategy provides opportunities to record long-term continuous electrophysiological signals in real-life conditions for various smart monitoring systems.
Artificial scent screening systems (known as electronic noses, E‐noses) have been researched extensively. A portable, automatic, and accurate, real‐time E‐nose requires both robust cross‐reactive sensing and fingerprint pattern recognition. Few E‐noses have been commercialized because they suffer from either sensing or pattern‐recognition issues. Here, cross‐reactive colorimetric barcode combinatorics and deep convolutional neural networks (DCNNs) are combined to form a system for monitoring meat freshness that concurrently provides scent fingerprint and fingerprint recognition. The barcodes—comprising 20 different types of porous nanocomposites of chitosan, dye, and cellulose acetate—form scent fingerprints that are identifiable by DCNN. A fully supervised DCNN trained using 3475 labeled barcode images predicts meat freshness with an overall accuracy of 98.5%. Incorporating DCNN into a smartphone application forms a simple platform for rapid barcode scanning and identification of food freshness in real time. The system is fast, accurate, and non‐destructive, enabling consumers and all stakeholders in the food supply chain to monitor food freshness.
Soft electronics that seamlessly interface with skin are of great interest in health monitoring and human-machine interfaces. However, achieving mechanical softness, skin adhesiveness, and high conductivity concurrently has always been a major challenge due to the difficulty in bonding dissimilar materials while retaining their respective properties. Herein, the mechanically interlocked hydrogel-elastomer hybrid is reported as a viable solution to this problem. Hydrogels with low moduli and high adhesiveness were employed as the substrate, while porous elastomer webs were used as matrices to load conductive films and lock the hydrogels through a mechanically interlocked structure. The bonding strength between hydrogel and elastomer in the interlocking hybrid structure was 14.3 times of that of physical stacking method. As a proof of concept, interlocking hybrids were used as on-skin electrodes for electrophysiological signals recording including electromyography and electrocardiogram.The robust hybrid electrodes still well detect signals after multiple cycles. The proposed
Plasticity of thermoset polymers has been realized by introducing exchangeable bonds, and the plasticity is mostly triggered via heat or UV light. Visible light is a relatively mild trigger that has not been used to induce plasticity in polymer materials. Herein, thermoset polyurethanes (PUs) containing diselenide bonds are fabricated that possess visible light-induced plasticity along with shape memory behavior. A series of PUs with different diselenide bond contents were tested and their shape memory properties and plasticity varied. With a higher diselenide bond content, both shape memory and light-induced plasticity are achieved. By combining these two properties, reshaping the permanent shapes of the PUs is easier. Compared with heat or UV light, visible light has the advantage of spatial control. For instance, a pattern of visible light was introduced by a commercial projector to demonstrate facile reshaping of the materials. Because visible light can be introduced via various methods, PUs with visible light-induced plasticity have great potential applications.
Noninvasive and seamless interfacing between the sensors and human skin is highly desired for wearable healthcare. Thin-film-based soft and stretchable sensors can to some extent form conformal contact with skin even under dynamic movements for high-fidelity signals acquisition. However, sweat accumulation underneath these sensors for long-term monitoring would compromise the thermal-wet comfort, electrode adherence to the skin, and signal fidelity. Here, we report the fabrication of a highly thermal-wet comfortable and conformal silk-based electrode, which can be used for on-skin electrophysiological measurement under sweaty conditions. It is realized through incorporating conducting polymers poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) into glycerol-plasticized silk fiber mats. Glycerol plays the role of tuning the mechanical properties of silk fiber mats and enhancing the conductivity of PEDOT:PSS. Our silk-based electrodes show high stretchability (>250%), low thermal insulation (∼0.13 °C·m2·W–1), low evaporative resistance (∼23 Pa·m2·W–1, 10 times lower than ∼1.3 mm thick commercial gel electrodes), and high water-vapor transmission rate (∼117 g·m–2·h–1 under sweaty conditions, 2 times higher than skin water loss). These features enable a better electrocardiography signal quality than that of commercial gel electrodes without disturbing the heat dissipation during sweat evaporation and provide possibilities for textile integration to monitor the muscle activities under large deformation. Our glycerol-plasticized silk-based electrodes possessing superior physiological comfortability may further engage progress in on-skin electronics with sweat tolerance.
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