Ultrasensitive stretchable patches for joint motion monitoring

Wearable devices have great application potential in the next generation of smart portable electronics,especially in the fields of medical monitoring,soft robotics,artificial intelligence,and human-machine interfaces.Piezoelectric flexible strain sensors are key components of wearable devices.However,existing piezoelectric flexible strain sensors have certain limitations in weak signal monitoring due to their large modulus and low sensitivity.To solve this problem,the concept of Kirigami(paper-cutting)was introduced in this study to design the sensor structure.By comparing the Kirigami structures of different basic structures,the serpentine structure was determined as the basic configuration of the sensor.The serpentine structure not only provides excellent tensile properties,but also significantly improves the sensitivity of the sensor,which performs well in monitoring weak signals.On this basis,the adhesion properties of the flexible sensor were analyzed and tested,and the optimal ratio of the substrate was selected for preparation.In addition,a low-cost and rapid prototyping process for stretchable patches was established in this study.Using this technology,we prepared the sensor device and tested its performance.Finally,we successfully developed a flexible sensor with a sensitivity of 0.128 mV/μɛand verified its feasibility for wrist joint motion monitoring applications.This result opens up new avenues for the recovery care of tenosynovitis patients after surgery.

Triboelectric gait sensing analysis system for self-powered IoT-based human motion monitoring

Quantitative analysis of gait parameters,such as stride frequency and step speed,is essential for optimizing physical exercise for the human body.However,the current electronic sensors used in human motion monitoring remain constrained by factors such as battery life and accuracy.This study developed a self-powered gait analysis system(SGAS)based on a triboelectric nanogenerator(TENG)fabricated electrospun composite nanofibers for motion monitoring and gait analysis for regulating exercise programs.The SGAS consists of a sensing module,a charging module,a data acquisition and processing module,and an Internet of Things(IoT)platform.Within the sensing module,two specialized sensing units,TENG-S1 and TENG-S2,are positioned at the forefoot and heel to generate synchronized signals in tandem with the user's footsteps.These signals are instrumental for real-time step count and step speed monitoring.The output of the two TENG units is significantly improved by systematically investigating and optimizing the electrospun composite nanofibers'composition,strength,and wear resistance.Additionally,a charge amplifier circuit is implemented to process the raw voltage signal,consequently bolstering the reliability of the sensing signal.This refined data is then ready for further reading and calculation by the micro-controller unit(MCU)during the signal transmission process.Finally,the well-conditioned signals are wirelessly transmitted to the IoT platform for data analysis,storage,and visualization,enhancing human motion monitoring.

Multifunctional Liquid Metal Active Material for Wound Repair and Motion Monitoring via Free Radical Polymerization Assembly

Bacterial infections and excessive oxidative stress seriously hinder the healing of skin wounds.Traditional wound dressings can only serve as physical barriers and lack active molecules essential for actively promoting wound healing.Herein,an antibacterial and antioxidant liquid metal inorganic active material is developed for wound repair through in situ polymerization of chitosan/acrylic acid precursor solution initiated by tannic acid-coated liquid metal nanoparticles,without extra initiators and ultraviolet (UV) light.The tannic acid component enables the inorganic active material to exhibit antioxidant property,which can remove 90% of free radicals and relieve cellular oxidative stress.The chitosan component endows the inorganic active material with antibacterial property,effectively inhibiting the growth of Staphylococcus aureus and Escherichia coli (killing ratio: 90%).In vivo experiment demonstrates that this inorganic active material can promote the healing of Staphylococcus aureus-infected wound,achieving a closure rate of 98.16% on the 9th day.Meanwhile,this inorganic active material exhibits good electrical conductivity,enabling timely and stable monitoring of human joint movements.This work offers a simple strategy for developing multifunctional inorganic active material,which holds great potential for wound repair and motion monitoring.

A low-cost, printable, and stretchable strain sensor based on highly conductive elastic composites with tunable sensitivity for human motion monitoring

Strain sensors with high stretchability, broad strain range, high sensitivity, and good reliability are desirable, owing to their promising applications in electronic skins and human motion monitoring systems. In this paper, we report a high- performance strain sensor based on printable and stretchable electrically con- ductive elastic composites. This strain sensor is fabricated by mixing silver-coated polystyrene spheres （PS@Ag） and liquid polydimethylsiloxane （PDMS） and screen-printed to a desirable geometry. The strain sensor exhibits fascinating comprehensive performances, including high electrical conductivity （1.65 × 104 S/m）, large workable strain range （〉 80%）, high sensitivity （gauge factor of 17.5 in strain of 0%-10%, 6.0 in strain of 10%-60% and 78.6 in strain of 60%-80%）, inconspicuous resistance overshoot （〈 15%）, good reproducibility and excellent long-term stability （1,750 h at 85℃/85% relative humidity） for PS@Ag/PDMS-60, which only contains - 36.7 wt.% of silver. Simultaneously, this strain sensor provides the advantages of low-cost, simple, and large-area scalable fabrication, as well as robust mechanical properties and versatility in applications. Based on these performance characteristics, its applications in flexible printed electrodes and monitoring vigorous human motions are demonstrated, revealing its tremendous potential for applications in flexible and wearable electronics.

A high-performance, single-electrode and stretchable piezotriboelectric hybrid patch for omnidirectional biomechanical energy harvesting and motion monitoring

Triboelectric nanogenerators(TENGs)have recently drawn much attention in the field of biomechanical energy harvesting and motion monitoring.However,the electrode stretchability and contact-separation model induced complicated packed structure remain a problem that heavily affects output performance during various human movements and requires to be urgently addressed.Here,a single-electrode piezotriboelectric hybrid nanogenerator(SEP-TENG)integrated with stretchable liquid-metal metal electrodes is reported,which simultaneously achieves outstanding energy harvesting performance and skincomfort human motion monitoring.A polarized piezoelectric BaTiO_(3)/silicon rubber(SR)composites film is served as the effective negative tribomaterial,benefiting from the improved dielectric constant and piezoelectric charge transfer,the optimized SEP-TENG generates a high peak power density of 5.7 W/m^(2) while contacted with human skin.Besides,owing to the ultralow Young's modulus of the SR encapsulation layer and tribo-piezoelectric hybrid layer,the homogeneous integrated multilayer composite serves no break till a 745%elongation,promoting that the SEP-TENG could effectively harvest biomechanical energy and realize stable power supplying for wearable electronics even under large deformation state.Furthermore,the SEP-TENG could comfortably attach to the finger joints and collect bending energy.This work provides a novel design methodology for a single-electrode TENG to realize omnidirectional biomechanical energy harvesting and motion monitoring.

An Ultrasensitive, Durable and Stretchable Strain Sensor with Crack-wrinkle Structure for Human Motion Monitoring

Flexible strain sensor has promising features in successful application of health monitoring, electronic skins and smart robotics, etc.Here, we report an ultrasensitive strain sensor with a novel crack-wrinkle structure(CWS) based on graphite nanoplates(GNPs)/thermoplastic urethane(TPU)/polydimethylsiloxane(PDMS) nanocomposite. The CWS is constructed by pressing and dragging GNP layer on TPU substrate,followed by encapsulating with PDMS as a protective layer. On the basis of the area statistics, the ratio of the crack and wrinkle structures accounts for 31.8% and 9.5%, respectively. When the sensor is stretched, the cracks fracture, the wrinkles could reduce the unrecoverable destruction of cracks, resulting in an excellent recoverability and stability. Based on introduction of the designed CWS in the sensor, the hysteresis effect is limited effectively. The CWS sensor possesses a satisfactory sensitivity(GF=750 under 24% strain), an ultralow detectable limit(strain=0.1%) and a short respond time of 90 ms. For the sensing service behaviors, the CWS sensor exhibits an ultrahigh durability(high stability>2×10^(4) stretching-releasing cycles). The excellent practicality of CWS sensor is demonstrated through various human motion tests,including vigorous exercises of various joint bending, and subtle motions of phonation, facial movements and wrist pulse. The present CWS sensor shows great developing potential in the field of cost-effective, portable and high-performance electronic skins.

Highly sensitive flexible strain sensor based on microstructured biphasic hydrogels for human motion monitoring

Flexible strain sensors have been extensively used in human motion detection,medical aids,electronic skins,and other civilian or military fields.Conventional strain sensors made of metal or semiconductor materials suffer from insufficient stretchability and sensitivity,imposing severe constraints on their utilization in wearable devices.Herein,we design a flexible strain sensor based on biphasic hydrogel via an in-situ polymerization method,which possesses superior electrical response and mechanical performance.External stress could prompt the formation of conductive microchannels within the biphasic hydrogel,which originates from the interaction between the conductive water phase and the insulating oil phase.The device performance could be optimized by carefully regulating the volume ratio of the oil/water phase.Consequently,the flexible strain sensor with oil phase ratio of 80%demonstrates the best sensitivity with gauge factor of 33 upon a compressive strain range of 10%,remarkable electrical stability of 100 cycles,and rapid resistance response of 190 ms.Furthermore,the human motions could be monitored by this flexible strain sensor,thereby highlighting its potential for seamless integration into wearable devices.

Natural polymers based triboelectric nanogenerator for harvesting biomechanical energy and monitoring human motion

Triboelectric nanogenerator(TENG)has been proved as a promising energy harvester in recent years,but the challenges of exploring economically triboelectric materials still exist and have aroused interests of many researchers.In this paper,chitosan-silk fibroin-airlaid paper composite film(CSA film)was fabricated and then the CSA film based-triboelectric nanogenerator(CSA-TENG)was constructed,which presents an opportunity for natural polymers to be applied in triboelectric materials.Due to the excellent electron donating ability of CSA film,the CSA-TENG can harvest environmental energy with a high efficiency.More importantly,the as-designed CSA film based dual-electrode triboelectric nanogenerator(CSA-D-TENG)is successfully assembled into hand clapper and trampoline to harvest mechanical energies generated by human bodies,it is also capable of monitoring human movement while harvesting biomechanical energies.This work provides a simple and environmental-friendly way to develop TENG for biomechanical energies harvesting and human motion monitoring.

An integrated portable bio-monitoring system based on tough hydrogels for comprehensive detection of physiological activities

Advanced soft ion-conducting hydrogels have been developed rapidly in the integrated portable health monitoring equipment due to their higher sensitivity,sensory traits,tunable conductivity,and stretchability for physiological activities and personal healthcare detection.However,traditional hydrogel conductors are normally susceptible to large deformation and strong mechanical stress,which leads to inferior electro-mechanical stability for real application scenarios.Herein,a strong ionically conductive hydrogel(poly(vinyl alcohol)-boric acid-glycerol/sodium alginate-calcium chloride/electrolyte ions(PBG/SC/EI))was designed by engineering the covalently and ionically crosslinked networks followed by the salting-out effect to further enhance the mechanical strength and ionic conductivity of the hydrogel.Owing to the collective effects of the energy-dissipation mechanism and salting-out effect,the designed PBG/SC/EI with excellent structural integrity and robustness exhibits exceptional mechanical properties(elongation at break for 559.1%and tensile strength of 869.4 kPa)and high ionic conductivity(1.618 S·m^(-1)).As such,the PBG/SC/EI strain sensor features high sensitivity(gauge factor=2.29),which can effectively monitor various kinds of human motions(joint motions,facial micro-expression,faint respiration,and voice recognition).Meanwhile,the hydrogel-based Zn||MnO_(2)battery delivers a high capacity of 267.2 mAh·g^(-1)and a maximal energy density of 356.8 Wh·kg^(-1)associated with good cycle performance of 71.8%capacity retention after 8000 cycles.Additionally,an integrated bio-monitoring system with the sensor and Zn||MnO_(2)battery can accurately identify diverse physiological activities in a real-time and non-invasive way.This work presents a feasible strategy for designing high-performance conductive hydrogels for highly-reliable integrated bio-monitoring systems with excellent practicability.

Biocompatible liquid metal coated stretchable electrospinning film for strain sensors monitoring system

Liquid metals(LMs)are potential inorganic materials which could be applied in flexible and deformable electronics owing to their fluidity,low viscosity,high metallic conductivity,and low toxicity.However,recently reported sensing devices based on LMs required complex processes with high cost.Herein,a flexible three-dimensional(3 D)conductive network was prepared by coating LM droplets onto an electrospun thermoplastic polyurethane(TPU)fiber film.The LM is suspended between the TPU fibers and self-coalesces into a vertically buckled and laterally mesh-like structure,which provides good biocompatibility,conductivity,and stretchability simultaneously.The LM-TPU composite-filmbased flexible device demonstrates a multitude of desired features,such as a widely workable stretching range(0%-200%),sufficient sensitivity under stretching strain(gauge factor(GF)of 0.2 at 200%strain),and outstanding stability and durability(9000 cycles).In vitro biocompatibility experiments show that the LM-TPU composite film directly attached to the skin has excellent biocompatibility.Such strain sensorbased integrated monitoring systems could monitor human body motions in real time,such as muscle movement and joint motion,revealing application prospects in healthcare and human-machine interfacing.

Enhanced performance of triboelectric mechanical motion sensor via continuous charge supplement and adaptive signal processing

The development of automation industry is inseparable from the progress of sensing technology.As a promising self-powered sensing technology,the durability and stability of triboelectric sensor(TES)have always been inevitable challenges.Herein,a continuous charge supplement(CCS)strategy and an adaptive signal processing(ASP)method are proposed to improve the lifetime and robustness of TES.The CCS uses low friction brushes to increase the surface charge density of the dielectric,ensuring the reliability of sensing.A triboelectric mechanical motion sensor(TMMS)with CCS is designed,and its electrical signal is hardly attenuated after 1.5 million cycles after reasonable parameter optimization,which is unprecedented in linear TESs.After that,the dynamic characteristics of the CCS-TMMS are analyzed with error rates of less than 1%and 2%for displacement and velocity,respectively,and a signal-to-noise ratio of more than 35 dB.Also,the ASP used a signal conditioning circuit for impedance matching and analog-to-digital conversion to achieve a stable output of digital signals,while the integrated design and manufacture of each hardware module is achieved.Finally,an intelligent logistics transmission system(ILTS)capable of wirelessly monitoring multiple motion parameters is developed.This work is expected to contribute to automation industries such as smart factories and unmanned warehousing.

A wide-linear-range and low-hysteresis resistive strain sensor made of double-threaded conductive yarn for human movement detection

Yarn-based flexible strain sensors with advantages in wearability and integrability have attracted wide at-tention.However,it is still a big challenge to achieve yarn-based strain sensors with a wide linear strain range,low hysteresis,and durability synchronously that can be used for full range detection of human body motions.Herein,a new structure,double-threaded conductive yarn with rhythmic strain distribu-tion,is reported to markedly widen the linear strain range of microcrack-based stretchable strain sensors.A new method of winding and thermally adhering hot-melt filaments on the surface of the elastic fiber is used to achieve double-threaded yarn(DTY)with rhythmic strain distribution.The proposed strategy,the integration of heterogeneous materials,is reported to significantly reduce the mechanical hysteresis of composite yarns.Rhythmic strain distribution of the DTY during stretching causes multi-level micro-cracks in different regions of the carbon nanotube(CNT)conductive layer deposited on the surface of the DTY.Besides,the sensing performance of DTY-based strain sensor can be adjusted by designing the structural parameters.The final prepared flexible strain sensor has the advantages of a wide linear strain range(100%),great sensitivity(GF=12.43),low hysteresis,rapid response(158 ms),high repeatability(>2000 cycles at 50%strain),and hydrophobicity,etc.The sensor can monitor human motion repeatedly and stably well,and shows great advantages in flexible wearable devices.

A thermally flexible and multi-site tactile sensor for remote 3D dynamic sensing imaging

A flexible,multi-site tactile and thermal sensor(MTTS)based on polyvinylidene fluoride(resolution 50×50)is reported.It can be used to implement spatial mapping caused by tactile and thermal events and record the two-dimensional motion trajectory of a tracked target object.The output voltage and current signal are recorded as amapping by sensing the external pressure and thermal radiation stimulus,and the response distribution is dynamically observed on the three-dimensional interface.Through the mapping relationship between the established piezoelectric and pyroelectric signals,the piezoelectric component and the pyroelectric component are effectively extracted from the composite signals.The MTTS has a good sensitivity for tactile and thermal detection,and the electrodes have good synchronism.In addition,the signal interference is less than 9.5%and decreases as the pressure decreases after the distance between adjacent sites exceeds 200μm.The integration of MTTS and signal processing units has potential applications in human-machine interaction systems,health status detection and smart assistive devices.

基于非对称PVA/墨水/PE双层膜的光驱动柔性致动器和多功能传感器

聚乙烯醇/中国墨水混合物被均匀涂覆在聚乙烯薄膜上制备了结构稳定的双层软驱动器.由于两层材料的热膨胀系数的显著差异,在氙灯照射下,驱动器能以较快的响应速度实现较大的弯曲变形.通过改变光的强度以及结合尺蠖的仿生结构设计,机器人可以在不同的表面(如纸张和树叶)上实现各种形式的运动.同时在光的驱动下,它可以实现物体的捕获、表情的改变、象鼻的收缩与卷曲以及仿生花朵的开闭等.此外,基于双层驱动器良好的光热转换和灵敏的压力传感性能,它可以实现人体运动监测(如关节弯曲、呼吸、吞咽等),还能与光电转换装置集成.这种多功能、多驱动模式软机器人在可穿戴设备、交通运输、光电转换设备等应用领域具有巨大潜力.

Conductive Film with Flexible and Stretchable Capability for Sensor Application and Stealth Information Transmission

Flexible and wearable strain sensors for human-computer interaction,health monitoring,and soft robotics have drawn widespread attention to promising applications in the next generation of artificial intelligence devices.However,conventional semiconductor sensors are difficult to meet the requirements of flexibility and stretchability.Here,we reported a kind of novel and simple sensor based on layer-by-layer(LBL)method.Carbon nanotubes(CNTs)layer provides high ductility and stability in the process of tension sensing,while silver layer provides low initial resistance and fast reflecting in the process of tension sensing.LBL method ensures the uniformity of the conductive layer.The sensor has superior sheet resistance of 9.44Ω/sq.,high elongation at break of 104%.For sensing capability,the sensor has wide reflecting range of 60%,high gauge factor(GF)of 1000 up to 60%strain,fast reflecting time of 165 ms.Excellent reliability and stability have also been verified.It is also worth mentioning that the entire process does not require any expensive equipments,complicated processes or harsh experimental conditions.The above features provide an idea for large-scale application of flexible stretchable sensors.

Oxidating liquid metal interface integrated capacitive pressure detection

The characteristics of real-time monitoring and flexible integration based on passive capacitive detection are becoming the preferred sensing strategy for wearable devices.However,the currently designed capacitive sensors mostly focused on the bionic microstructures to improve sensitivity and measurement accuracy,while ignoring the inherent mechanical wear and resistance of multilayer structures.In this paper,an integrated monolithic capacitive pressure detection based on room temperature liquid metal is designed and fabricated,avoiding the tightness problem of the multi-layer structure.The oxidized paste-like liquid metal owning superior interfacial wetting properties can stably adhere to the surface of the porous framework.The gas-filled porous framework endows the capacitive sensor with a mechanical response of 0.0557 g with a response and recovery time of 1.26 and 0.63 s under a load condition of 150 Pa,and steadily maintained in 1600 cycle tests.Finally,the capacitive sensor is employed to detect human physiological signals and force shock responses,which could clearly distinguish different action signals,providing a new platform for the subsequent development and design of integrated capacitive sensors.

One-step and Continuous Fabrication of Coaxial Piezoelectric Fiber for Sensing Application

Although there has been rapid advancement in piezoelectric sensors,challenges still remain in developing wearable piezoelectric sensors by a one-step,continuous and environmentally friendly method.In this work,a 1D flexible coaxial piezoelectric fiber was directly fabricated by melt extrusion molding,whose core and sheath layer are respectively slender steel wire(i.e.,electrode)and PVDF(i.e.,piezoelectric layer).Moreover,such 1D flexible coaxial piezoelectric fiber possesses short response time and high sensitivity,which can be used as a selfpowered sensor for bending and vibration sensing.More interestingly,such 1D flexible coaxial piezoelectric fiber(1D-PFs)can be further endowed with 3D helical structure.Moreover,a wearable and washable motion monitoring system can be constructed via braiding such 3D helical piezoelectric fiber(3D-PF)into commercial textiles.This work paves a new way for developing 1D and 3D piezoelectric fibers through a one-step,continuous and environmentally friendly method,showing potential applications in the field of sensing and wearable electronics.

Self-healing,Stretchable,Temperature-Sensitive and Strain-Sensitive Hydrogel-based Flexible Sensors

Flexible hydrogels have shown promise as strain sensors in medical monitoring,human motion detection and intelligent robotics.For a hydrogel strain sensor,certain challenges need to be urgently addressed for practical applications,such as the damage caused by external effects,leading to equipment failure,and the inability to perceive ambient temperature,resulting in single functionality.Herein,a stretchable,self-healing and dual temperature-strain sensitive hydrogel,with a physically-crosslinked network,is designed by constructing multiple dynamic reversible bonds.Graphene oxide(GO)and iron ions(Fe^(3+))act as dynamic bridges in the cross-linked network and are mediated by the covalent and hydrogen bonding,rendering excellent stretchability to the hydrogel.The reversible features of coordination interactions and hydrogen interactions endow excellent recoverability and self-healing properties.Moreover,the incorporated N-isopropyl acrylamide(NIPAM)provides excellent temperature responsiveness to the hydrogel,facilitating the detection of external temperature changes.Meanwhile,the hydrogels exhibited strain-sensitivity,with a wide working range of 1%-300%,fast response and electrical stability,which can be used as flexible sensors to monitor body motions,e.g.,speaking and the bending of finger,wrist,elbow and knee.Overall,the hydrogel possesses dual sensory capabilities,combining external temperature and strain,for potential applications in wearable multifunctional sensing devices.