Wearable multilead ECG sensing systems using on-skin stretchable and breathable dry adhesives

Electrocardiogram(ECG)monitoring is used to diagnose cardiovascular diseases,for which wearable electronics have attracted much attention due to their lightweight,comfort,and long-term use.This study developed a wearablemultilead ECG sensing system with on-skin stretchable and conductive silver(Ag)-coated fiber/silicone(AgCF-S)dry adhesives.Tangential and normal adhesion to pigskin(0.43 and 0.20 N/cm2,respectively)was optimized by the active control of fiber density and mixing ratio,resulting in close contact in the electrode–skin interface.The breathableAgCF-S dry electrodewas nonallergenic after continuous fit for 24 h and can be reused/cleaned(>100 times)without loss of adhesion.The AgCF encapsulated inside silicone elastomers was overlapped to construct a dynamic network under repeated stretching(10%strain)and bending(90°)deformations,enabling small intrinsic impedance(0.3,0.1 Hz)and contact impedance variation(0.7 k)in high-frequency vibration(70 Hz).All hard/soft modules of the multilead ECG system were integrated into lightweight clothing and equipped with wireless transmission for signal visualization.By synchronous acquisition of I–III,aVR,aVL,aVF,and V4 lead data,the multilead ECG sensing system was suitable for various scenarios,such as exercise,rest,and sleep,with extremely high signal-to-noise ratios.

Laser-induced jigsaw-like graphene structure inspired by Oxalis corniculata Linn.leaf

The laser scribing of polyimide(PI, Kapton) film is a new, simple and effective method for graphene preparation. Moreover,the superhydrophobic surface modification can undoubtedly widen the application fields of graphene. Herein, inspired by the hydrophobic and self-cleaning properties of natural Oxalis corniculata Linn. leaves, we propose a novel bionic manufacturing method for superhydrophobic laser-induced graphene(LIG). By tailoring the geometric parameters(size, roughness and height/area ratio) and chemical composition, the three-dimensional(3D) multistage LIG, i.e., with micro-jigsaw-like and porous structure, can deliver a static water contact angle(WCA) of 153.5° ± 0.6°, a water sliding angle(WSA) of 2.5° ±0.5°, and great superhydrophobic stability lasting for 100 days(WCAs ≈ 150°). This outstanding water repellency is achieved by the secondary structure of jigsaw-like LIG, a porous morphology that traps air layers at the solid–liquid interface. The robust self-cleaning and anti-stick functions of 3D bionic and multistage LIG are demonstrated to confirm its great potential in wearable electronics.

A Deep Learning-Enabled Skin-Inspired Pressure Sensor for Complicated Recognition Tasks with Ultralong Life

Flexible full-textile pressure sensor is able to integrate with clothing directly,which has drawn extensive attention from scholars recently.But the realization of flexible full-textile pressure sensor with high sensitivity,wide detection range,and long working life remains challenge.Complex recognition tasks necessitate intricate sensor arrays that require extensive data processing and are susceptible to damage.The human skin is capable of interpreting tactile signals,such as sliding,by encoding pressure changes and performing complex perceptual tasks.Inspired by the skin,we have developed a simple dip-and-dry approach to fabricate a full-textile pressure sensor with signal transmission layers,protective layers,and sensing layers.The sensor achieves high sensitivity(2.16 kPa^(−1)),ultrawide detection range(0 to 155.485 kPa),impressive mechanical stability of 1 million loading/unloading cycles without fatigue,and low material cost.The signal transmission layers that collect local signals enable real-world complicated task recognition through one single sensor.We developed an artificial Internet of Things system utilizing a single sensor,which successfully achieved high accuracy in 4 tasks,including handwriting digit recognition and human activity recognition.The results demonstrate that skin-inspired full-textile sensor paves a promising route toward the development of electronic textiles with important potential in real-world applications,including human–machine interaction and human activity detection.

Cutting performance of surgical electrodes by constructing bionic microstriped structures

Surgical electrodes rely on thermal effect of high-frequency current and are a widely used medical tool for cutting and coagulating biological tissue.However,tissue adhesion on the electrode surface and thermal injury to adjacent tissue are serious problems in surgery that can affect cutting performance.A bionic microstriped structure mimicking a banana leaf was constructed on the electrode via nanosecond laser surface texturing,followed by silanization treatment,to enhance lyophobicity.The effect of initial,simple grid-textured,and bionic electrodes with different wettabilities on tissue adhesion and thermal injury were investigated using horizontal and vertical cutting modes.Results showed that the bionic electrode with high lyophobicity can effectively reduce tissue adhesion mass and thermal injury depth/area compared with the initial electrode.The formation mechanism of adhered tissue was discussed in terms of morphological features,and the potential mechanism for antiadhesion and heat dissipation of the bionic electrode was revealed.Furthermore,we evaluated the influence of groove depth on tissue adhesion and thermal injury and then verified the antiadhesion stability of the bionic electrode.This study demonstrates a promising approach for improving the cutting performance of surgical electrodes.

Scorpion-inspired dual-bionic,microcrack-assisted wrinkle based laser induced graphene-silver strain sensor with high sensitivity and broad working range for wireless health monitoring system

Scorpions,through ruthless survival of the fittest,evolve the unique ability to quickly locate and hunt prey with slit receptors near the leg joints and a sharp sting on the multi-freedom tail.Inspired by this fantastic creature,we herein report a dual-bionic strategy to fabricate microcrack-assisted wrinkle strain sensor with both high sensitivity and stretchability.Specifically,laserinduced graphene(LIG)is transferred from polyimide film to Ecoflex and then coated with silver paste using the casting-andpeeling and prestretch-and-release methods.The shape-adaptive and long-range ordered geometry(e.g.,amplitude and wavelength)of dual-bionic structure is prestrain-tuned to optimize the superfast response time(~76 ms),high sensitivity(gauge factor=223.6),broad working range(70%–100%),and good reliability(>800 cycles)of scorpion-inspired strain sensor,outperforming many LIG-based materials and other bionic sensors.The alternate reconnect/disconnect behaviors of slit-organlike microcracks in the mechanical weak areas initiate tremendous resistance changes,whereas the scorpion-tail-like wrinkles act as a“bridge”connecting the adjacent LIG resistor units,enabling reversible resilience and unimpeded electrical linkages over a wide strain range.Combined with the self-developed miniaturized,flexible,and all-in-one wireless transmission system,a variety of scenarios such as large body movements,tiny pulse,and heartbeat are real-time monitored via bluetooth and displayed in the client-sides,revealing a huge promise in future wearable electronics.

Direct mask-free fabrication of patterned hierarchical graphene electrode for on-chip micro-supercapacitors

Graphene-based electrodes with rational structural design have shown extraordinary prospect for en-hanced electrical double-layer capacitance of micro-supercapacitors(MSCs).Herein,a facile fabrication method for flexible planar MSCs based on hierarchical graphene was demonstrated by using a laser-treated membrane for electrode patterning,complemented with hierarchical electrode configuration tak-ing full advantages of size-determined functional graphene.The in-plane interdigital shape of MSCs was defined through vacuum filtration with the assistance of the functionalized polypropylene(PP)mem-brane.The hierarchical graphene films were built by macroscopic assembly based on size effect of differ-ent lateral sized graphene sheets(rGO-LSL).The sample of MSCs based on rGO-L SL(MSCs-LSL)exhibited excellent volumetric capacitance of 6.7 F cm^(−3) and high energy density of 0.37 mWh cm−3.The MSCs-LSL presented superb flexibility and cycling stability with no capacitance deteroriated after 2000 cycles.This newly developed fabrication strategy is of good scalability and designability to manufacture flexible elec-trode for MSCs with customized shapes,while the construction of hierarchical graphene can enlighten the structural design of analogous two-dimensional materials for potential advanced electronics.

Superhydrophobic Purple Orchid Leaves:Variation in Surface Morphology During the Vegetation Stages Leading to Diversity in Wettability

Learning hydrophobic phenomena from nature is always a promising approach to design the superhydrophobic surface.Purple orchid leaf which processes superhydrophobicity is an ideal plant model,and through mimicking its structure,the surface with excellent hydrophobicity is able to be obtained.However,the unclear of the diversity in wettability during the different vegetation stages and the absence of its relation to the surface morphology limits the further enhancement of the inspired structure.Here,we analyze the wettability difference as the leaf grows from tender to mature and then to senescent.Combining with the variation of surface morphology and chemical composition,the well-developed micro-scale basic unit bumps with dense nano-scale waxy layer on the surface are proven to be responsible for the best hydrophobicity of the mature leaf.The presence of the undeveloped or damaged micro-nano hierarchical structure reduces the formation of air pockets at the interface,leading to the decrease of the wettability for leaves at other stages.Moreover,by fabricating artificial leaves,the nano-waxy layer is proved to be more effective than that of the micro-bumps on the surface wettability.The results of study are of a great significance for guiding the design and fabrication of plant-inspired bionic superhydrophobic surface.

Capillary Performance of Nanoporous Aluminum Braided Wicks Prepared by Anodic Oxidation

With the rapid development of two-phase heat exchangers,the further improvement of the capillary performance of their internal wick faces a great challenge.As an important technology in the surface treatment of aluminum alloys,anodic oxidation has been widely used to develop various functional nanostructures.In this study,nanopores with diameters of 30–40 nm were fabricated on the surface of aluminum fibers through anodic oxidation under an oxalic acid system.Results showed that anodizing increased the specific surface area of the aluminum braid by 163 times,and changed its surface wettability from hydrophobic to superhydrophilic.A significant reduction in the effective capillary radius can substantially increase the capillary force of aluminum braids on the basis of capillary theory.Therefore,the nanoporous aluminum braids can be used as a novel wick in the vapor chamber to improve its capillary performance.Capillary rate-of-rise tests with ethanol and acetone were performed to characterize the capillary of this novel wick structure.Infrared thermal imaging was utilized to monitor the capillary rise of aluminum braided wicks.The capillary force of the anodized wicks was greater than that of a normal wick,and the maximum capillary rise height was 81 mm.The nanoporous aluminum braided wicks prepared by anodizing could be applied in heat transfer.