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.
Diselenide bonds are dynamic covalent bonds. Their metathesis can be induced by irradiation with visible light and likely proceeds through a radical mechanism, as the exchange reaction between two different diselenides was suppressed by the addition of the radical scavenger 2,2,6,6‐tetramethylpiperidine N‐oxide (TEMPO).
Underwater vital signs monitoring of respiratory rate, blood pressure, and the heart's status is essential for healthcare and sports management. Real‐time electrocardiography (ECG) monitoring ...underwater can be one solution for this. However, the current electrodes used for ECGs are not suitable for aquatic applications since they may lose their adhesiveness to skin, stable conductivity, or/and structural stability when immersed into water. Here, the design and fabrication of water‐resistant electrodes to repurpose stretchable electrodes for applications in an aquatic environment are reported. The electrodes are composed of stretchable metal–polymer composite film as the substrate and dopamine‐containing polymer as a coating. The polymer is designed to possess underwater adhesiveness from the dopamine motif, water stability from the main scaffold, and ionic conductivity from the carboxyl groups for signal transmission. Stable underwater conductivity and firm adhesion to skin allow the electrodes to collect reliable ECG signals under various conditions in water. It is shown that wearable devices incorporated with the water‐resistant electrodes can acquire real‐time ECG signals during swimming, which can be used for revealing the heart condition. These water‐resistant electrodes realize underwater detection of ECG signals and can be used for health monitoring and sports management during aquatic activities.
Water‐resistant stretchable electrodes are fabricated with a specially designed polymer. The polymer is adhesive underwater to bridge the electrode and skin, and ionic‐conductive to transmit electrophysiological signals. The conformal electrodes realize reliable electrocardiography (ECG) detection when moving the body or being impacted with water flow, which enables stable wireless real‐time ECG collection during swimming with a wearable device.
Wavelength‐controlled dynamic processes are mostly based on light‐triggered isomerization or the cleavage/formation of molecular connections. Control over dynamic metathesis reactions by different ...light wavelengths, which would be useful in controllable dynamic chemistry, has rarely been studied. Taking advantage of the different bond energies of disulfide and diselenide bonds, we have developed a wavelength‐driven exchange reaction between disulfides and diselenides, which underwent metathesis under UV light to produce Se−S bonds. When irradiated with visible light, the Se−S bonds were reversed back to those of the original reactants. The conversion of the exchange depends on the wavelength of the incident light. This light‐driven metathesis chemistry was also applied to tune the mechanical properties of polymer materials. The visible‐light‐induced reverse reaction was compatible with reductant‐catalyzed disulfide/diselenide metathesis, and could be utilized to develop a dissipative system with light as the energy input.
Controlled metathesis: Metathesis between disulfide and diselenide bonds was realized under irradiation, and the conversion of the exchange reaction could be controlled by modulating the wavelength of the light. This chemistry was applied to polymer materials to control the cleavage of polymers from a distance.
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.
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 are employed as the substrate, while porous elastomer webs are used as matrices to load conductive films and lock the hydrogels through a mechanically interlocked structure. The bonding strength between the hydrogel and elastomer in the interlocking hybrid structure is 14.3 times of that obtained via the physical stacking method. As a proof of concept, interlocking hybrids are used as on‐skin electrodes for electrophysiological signal recording including electromyography and electrocardiography. The robust hybrid electrodes are able to detect signals after multiple cycles. The proposed strategy not only is an effective approach to achieve interlocking structures, but also provides a new perspective for soft and stretchable electronics.
A novel hydrogel–elastomer hybrid is developed by mechanical interlocking. Porous elastomer webs are used as matrices to load conductive materials and lock hydrogels through an interlocking structure to achieve mechanically soft and skin‐adhesive electrodes. The interlocking hybrid is used as an on‐skin electrode for recording electrophysiological signals.
The COVID-19 pandemic raised wide concern from all walks of life globally. Social media platforms became an important channel for information dissemination and an effective medium for public ...sentiment transmission during the COVID-19 pandemic.
Mining and analyzing social media text information can not only reflect the changes in public sentiment characteristics during the COVID-19 pandemic but also help the government understand the trends in public opinion and reasonably control public opinion.
First, this study collected microblog comments related to the COVID-19 pandemic as a data set. Second, sentiment analysis was carried out based on the topic modeling method combining latent Dirichlet allocation (LDA) and Bidirectional Encoder Representations from Transformers (BERT). Finally, a machine learning linear regression (ML-LR) model combined with a sparse matrix was proposed to explore the evolutionary trend in public opinion on social media and verify the high accuracy of the model.
The experimental results show that, in different stages, the characteristics of public emotion are different, and the overall trend is from negative to positive.
The proposed method can effectively reflect the characteristics of the different times and space of public opinion. The results provide theoretical support and practical reference in response to public health and safety events.
We theoretically and experimentally demonstrate an all-fiber multi-channel ultrasonic sensor using a switchable fiber Bragg gratings (FBGs) filter in an erbium-doped fiber laser (EDFL). The FBGs are ...not only used as the filter to determine the laser wavelength, but also as the sensing element to induce the intensity response of the lasing line via cavity loss modulation from the ultrasound-induced relative spectral shift of the matched FBGs. The switchable FBGs filter consists of a tuning FBG and several sensing FBGs. Multi-channel ultrasound detection is achieved via this filter by tuning an FBG to scan the spectra of multiple sensing FBGs. The ultrasonic-detection channel can be flexibly and efficiently switched via tuning the tunable FBG to match with any one of the sensing FBGs. A novel dynamic response model of the EDFL based on wavelength-dependent gain is proposed and developed to study the effects of different spectrally matched FBG positions and the consistency of the ultrasound response of each detection channel. The theoretical results show that the optimal sensing position is at the overlapping regions of spectra when the slope of the FBGs is greatest and the laser power is relatively high. Meanwhile, the consistency of the ultrasound response for each detection channel is influenced by the laser-resonance condition of the EDFL and can be optimized by adjusting the laser-cavity loss. Such theoretical results are well-verified experimentally. This sensor-laser-integrated system achieves high ultrasonic detection response since cavity-loss modulation is related to the amplifying effect of the laser. Using this method, an eight-channel switchable ultrasonic-sensing system has been demonstrated, covering nearly a 16-nm spectral range. By further controlling the cavity loss in the laser system, the consistency of ultrasonic response of each detection channel was optimized. The proposed all-fiber system has multiple- detection channels in a single laser system and consistent ultrasonic-detection response at each channel; it shows great potential for fiber-optic-ultrasonic-detection applications.
In this study, we propose and demonstrate a multipoint fiber-optic laser-ultrasound transducer based on fiber waist-enlarged tapers (WETs), which are fabricated by taper fusing two single-mode ...fibers. The WET structure can effectively extract some of the light energy from the fiber core and transfer it to the cladding to form a series of higher-order modes that can be used to excite ultrasound waves. The light energy in the cladding can be absorbed and converted into ultrasound waves by the photoacoustic composite coating on the fiber near WET. The coupling efficiency of the WET is dependent upon its taper length and, therefore, can be easily controlled by the splicer during fabrication. Thus, by controlling coupling efficiencies of the WETs, a multipoint laser-ultrasound actuator with a balanced signal strength can be obtained. We constructed a prototype of the actuator and successfully generated ultrasound waves with balanced strengths at four points by connecting four WETs with coupling ratios of 25.24%, 32.25%, 49.52%, and 90.62% in a fiber link. This multipoint laser-ultrasound actuator is simple to fabricate and provides a balanced ultrasonic signal strength, and thus, has various potential applications in fiber-optic active ultrasound testing technologies.
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