Multifunctional Strain Sensors Research Articles

Self-powered and multi-mode flexible sensing film with patterned conductive network for wireless monitoring in healthcare

The flexible and multi-functional strain sensors have attracted extensive research attention due to their promising applications in various wearable electronics. However, it remains a huge challenge to design and fabricate the self-powered flexible sensing micro-system based on a single multifunctional material to relieve the dependence on external rigid and heavy battery. Herein, a self-powered and multi-mode flexible sensing system integrated with triboelectric nanogenerator (TENG), flexible solid-state supercapacitors (FSSC) and strain sensor is developed based on thermoplastic polyurethane film with asymmetric and cross conductive networks through a facile screen printing process. The unique conductive network endows the prepared strain sensor with an independent anisotropic response to the strain applied in different directions. The TENG in single-electrode mode is presented to generate electricity from ubiquitously bio-mechanical energy and stored it in the FSSC immediately, realizing continuous green power supply for the sensor. As proof-of-concept, an all-in-one smart device consisting of energy supply and sensing module is constructed, demonstrating the great convenience and feasibility for practical application in sustainable wearable electronics. Benefiting from the excellent comprehensive sensing performance, the wireless wearable device assembled by the prepared sensor exhibits excellent detection and recognition for various human motion, expressions, phonation, and physiological signal, revealing the broad potential applications in rehabilitation training, human-machine interaction and medical diagnosis. This work proposes an innovative and scalable approach to manufacture multifunctional micro-systems, which will bring new vitality and more possibilities to a new generation of wearable electronics.

Gridization-Driven Mesoscale Self-Assembly of Conjugated Nanopolymers into Luminescence-Anisotropic Photonic Crystals.

Organic semiconducting emitters integrated with butterfly-mimetic photonic crystals (PhCs) are fascinating for dramatic advantages over light outcoupling efficiency and multifunctional strain sensors, as well as the key step toward electrically pumped lasers. Herein, an unprecedentedly direct mesoscale self-assembly into 1D PhCs is reported through a covalently gridization-driven approach of wide-bandgap conjugated polymers. A simple solvent-casting procedure allows for in situ self-assembly of the state-of-the-art conjugated nanopolymer, poly{[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]grid}-co-{[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]grid} (PODPFG), into well-defined multilayer architectures with an excellent toughness (30-40 J m-3 ). This ordered meso-architecture shows a typical Bragg-Snell diffraction behavior to testify the PhC nature, along with a high effective refractive index (1.80-1.88) and optical transmittance (85-87%). The PhC films also exhibit an angle-dependent blue/green photoluminescence switching, an electroluminescence efficiency enhancement by 150-250%, and an amplified spontaneous emission enhancement with ultralow waveguide loss coefficient (2.60 cm-1 ). Gridization of organic semiconductors offers promising opportunities for cross-scale morphology-directed molecular design in multifunctional organic mechatronics and intelligences.

Rational structural design of vanillin based vitrimers in one-pot to facilely fabricate highly stretchable and sensitive composite strain sensor

The preparation of high performance and multifunctional strain sensors by a facile fabrication process is highly desirable but still challenging. In this study, vanillin based vitrimers were simply synthesized in one-pot by the combination of thiol-epoxy and amine-aldehyde reactions, which was used for strain sensor fabrication. The reaction kinetics were extensively investigated by 1H NMR analysis to demonstrate the feasibility to prepare vitrimers in one-pot. The physicochemical properties and dynamic natures of vanillin based vitrimers were then analyzed by various techniques, such as FTIR, DSC and rheometer. The mechanical properties of vitrimers were tunable via controlling the structure of crosslinkers. Moreover, it exhibited a strong UV-adsorption ability to potentially protect the human skins. Due to the enhanced interfacial interaction between vitrimers and silver nanowire layers, and the dynamic feature of Schiff base, the fabrication of strain sensors with sandwich-structures could be facilely realized. The strain sensors show a wide linear response range (0–100%) and a high gauge factor (15.8), which was comparable to previous sensors prepared by complicated steps. This study has demonstrated the potential to combine dynamic covalent chemistry and sustainability to overcome the general challenges in the fabrication of high-performance strain sensors.

A self-healing, recyclable and conductive gelatin/nanofibrillated cellulose/Fe3+ hydrogel based on multi-dynamic interactions for a multifunctional strain sensor.

Conductive hydrogels have emerged as promising material candidates for multifunctional strain sensors, attributed to their similarity to biological tissues, good wearability, and high accuracy of information acquisition. However, it is difficult to simultaneously manufacture conductive hydrogel-based multifunctional strain sensors with the synergistic properties of reliable healability for long-term usage and environmental degradability/recyclability for decreasing the electronic waste. This work reports a facile strategy to engineer a self-healing, recyclable and conductive strain sensor by virtue of molecular-level multi-dynamic interactions (MMDIs) including Schiff base complexes, hydrogen bonds, and coordination bonds, which were fabricated using a dialdehyde TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl)-oxidized nanofibrillated cellulose (DATNFC) pre-reinforced gelatin nanocomposite hydrogel (gelatin/DATNFC hydrogel, GDH) followed by dipping in an Fe3+ aqueous solution. The MMDI strategy allows synchronous regulation of both bulk and interfacial interactions to obtain exciting properties that outperform those of conventional hydrogels, including extraordinary compressive stress (1310 kPa), intriguing self-healing abilities, and remarkable electrical conductivity. With these outstanding merits, the as-prepared gelatin/DATNFC/Fe3+ hydrogel (GDIH) is developed to be a multifunctional strain sensor with appealing strain sensitivity (GF = 2.24 under 6% strain) and compressive sensitivity (S = 1.14 kPa-1 under 15 kPa), which can be utilized to manufacture electronic skin and accurately discern subtle bodily motions, handwriting and personal signatures. Notably, this GDIH-based sensor also exhibited reliable self-healing properties for long-term usage, environmental degradability and complete recyclability for decreasing the electronic waste. In consideration of the extremely facile preparation process, biocompatibility, satisfactory functionalities, remarkable self-healing properties and recyclability, the emergence of the GDIH-based sensor is believed to propose a new strategy for the development of sustainable-multifunctional strain sensors and healthcare monitoring.

A wide sensing range and high sensitivity flexible strain sensor based on carbon nanotubes and MXene

Flexible and multifunctional strain sensors have attracted extensive concern owing to the promising applications in wearable devices, artificial intelligence, and health monitoring. However, the strain sensor with a high gauge factor (GF) and broad working range remains a big challenge. In this work, we developed a multifunctional strain sensor by incorporating carbon nanotubes (CNT) and MXene onto a porous polydimethylsiloxane (PDMS) sponge. The resultant PDMS/CNT@MXene sensor exhibits a wide sensing range (105% strain), high sensitivity (GF = 1939), rapid response speed (response/recovery time of 158/160 ms), sufficient reliability and stability under the repeated stretching, compression, and bending cycles. The sensor can be applied for detecting a variety of body actions as well as medical diagnosis, such as various joint movements, phonation detecting, pulse beats, and handwriting. Therefore, our present sensor demonstrates powerful potential applications in smart clothing, flexible electronics, and human health monitoring.

Highly Stretchable, Adhesive Ionic Liquid-Containing Nanocomposite Hydrogel for Self-Powered Multifunctional Strain Sensors with Temperature Tolerance.

The demand for wearable sensors consisting of multifunctional conductive hydrogels with fatigue resistance and adhesion properties is rising. More importantly, it is necessary to improve the freezing tolerance and dehydration resistance of hydrogels to avoid performance degradation in harsh environments. Herein, a robust nanocomposite ionogel was fabricated in [EMIM][Cl] ionic liquid and clay nanosheets were used as physical cross-linkers through rapid UV polymerization. The excellent mechanical properties, repeated self-adhesion to various substrates, freezing tolerance, and anti-drying properties were integrated into the nanocomposite ionic liquid hydrogel. The addition of clay nanosheets Laponite XLG endowed the ionogel with a high stretchability of up to 1200% and a tensile strength of up to 0.14 MPa, and the ionogel could be recovered when the external force was released. Ascribing to ionic liquids, the nanocomposite ionogel displayed ionic conductivity and temperature tolerance. An ionogel battery with a 0.72 V output voltage was formed by assembling the ionogel with a layer of zinc and copper sheet on each side to realize the conversion from chemical energy to electrical energy. The maximum voltage could reach 2.8 V when the four units are combined, which could provide energy for an LED bulb and could be used as a self-powered strain sensor under harsh conditions. In this work, a multifunctional ionogel self-powered sensor is proposed, which has potential applications in the fields of electronic skin, human-machine interaction, and biosensors over a wide temperature range.

Ultrathin and Highly Tough Hydrogel Films for Multifunctional Strain Sensors.

With good flexibility and biocompatibility, hydrogel-based sensors have been widely used in human motion detection, artificial intelligence, human-machine interface, and other fields. Previous research on hydrogel-based sensors has focused on improving the mechanical properties and signal transmission sensitivity. With the development of human smart devices, there is an increasing demand for hydrogel sensor comfort and more application functions, such as ultrathin structures and recognition functions for contact surfaces, which are realized with higher requirements for the thickness, flexibility, friction resistance, and biocompatibility of hydrogels. Inspired by the ultrathin and flexible characteristics of human organ biofilms, we constructed conductive hydrogel films by using the flim-casting and glycerol-H2O secondary hydration methods. This ultrathin structure enables the hydrogel films to have a high elongation at break of 523.3%, a stress of 3.5 MPa, and a good friction resistance. Combined with the excellent sensing properties (gauge factor = 2.1 and a response time of 200 ms), the hydrogel film-based sensor can not only record human motion signals but also recognize the surface texture and roughness of objects, such as glass, brushes, wood, and sandpaper with mesh sizes of 80, 50, and 24, accurately. In addition, this hydrogel film has a series of excellent properties such as UV shielding, antiswelling ability, and good biocompatibility. This research provides a novel way for the development of emerging soft-material smart devices, such as hydrogel-based electronic skin and soft robots.

Flexible and Anisotropic Strain Sensors with the Asymmetrical Cross-Conducting Network for Versatile Bio-Mechanical Signal Recognition.

Flexible strain sensors with high performance are actively and widely investigated for wearable electronic devices. However, the conventional sensors often suffer from a lack of detection of complex multidimensional strain, which severely limits their wide applications. To overcome this critical challenge, we propose a pattern design by screen printing to construct an asymmetrical cross-conductive network in the piezoresistive strain sensor, which can enhance the response to external stimuli in different directions. The unique network endows the prepared sensors with the excellent ability of instantaneous detection and accurate identification of multidimensional strains. Moreover, the sensor also demonstrates high sensitivity, fast response, an ultra-wide sensing range, and excellent stability and durability. Benefiting from the outstanding comprehensive performance of the prepared sensor, a full range of human actions (wink, smile, swallowing, and joint bending) and subtle bio-signals (pulse and breathing) are easily and accurately monitored. A wireless wearable device assembled by the sensor shows great potential applications in practical real-time physiological monitoring and intelligent mobile diagnosis for humans. This work provides an innovative and effective strategy for manufacturing flexible and multifunctional strain sensors to fully satisfy versatile applications of new-generation wearable electronic devices.

Highly sensitive strain sensor with wide strain range fabricated using carbonized natural wrapping yarns

In this work, we report a high-performance strain sensor with ultra-sensitivity under the subtle strain and large sensing strain range based on Ecoflex rubber and carbonized natural yarns. The flexible strain sensor based on wrapping yarn with carbon nanofiber yarn as sheath and natural silk yarn as core can capture ultralow detection limit (<0.01%) with a high gage factor of 307 and the excellent cycling stability. The wrapping yarn fabricated using cotton yarn as sheath and silk yarn as core endowed the sensor with wide strain range from 0.1% to 130%, high sensitivity for the subtle deformation, quick response time (<400 ms) and durability. Remarkably, the sensor can not only monitor the various human motions and physiological information, such as walking, breathing, pulses, speaking, but also distinguish the sound wave and damped vibration for structural safety. It is hopeful to develop the multifunctional strain sensors for widespread applications.

Ultralight, flexible and conductive silver nanowire/nanofibrillated cellulose aerogel for multifunctional strain sensor

Wearable strain sensors have drawn growing interest in the field of intelligent electronic devices because of their inherent advantages including miniaturization and portability. For practical applications, strain sensors with lightness, flexibility, and high sensitivity are urgently desired. Herein, the interconnected silver nanowires (AgNWs) are assembled into the nanofibrillated cellulose (NFC) aerogel through unidirectional freeze-drying yielding an ultralight and conductive AgNWs/NFC aerogel (SNA) with ordered pore orientation. After thermal welding, the SNA possesses unique electron transfer channels, which can efficiently eliminate the interfacial electrical resistance at the AgNWs junctions and bring an impressive conductivity enhancement for the composite aerogel. Benefiting from the synergy of the desired microstructure and superior conductivity of as-prepared aerogel, the derived sensor shows desirable sensitivity (3.86 kPa−1), fast response time (180 ms), ultralow density (less than 13.58 mg/cm3) and detection limit of 0.5% strain, and exceptional stability and durability (over 10,000 cycles). Significantly, the integrated conductive network in SNA simultaneously offers real-time monitoring of subtle deformations and electrophysiological signals, which enables the designs of wearable device, acoustic sensor, and vehicles’ speed and loading detector. The presented strategy opens up a new possibility for designing and manufacturing next-generation multifunctional strain sensor to bring the technology much closer to commercialization.

Self-Healable, Recyclable, and Ultrastrong Adhesive Ionogel for Multifunctional Strain Sensor.

Flexible electronic materials have aroused significant interest due to the need for flexible electronics in a variety of applications. However, several obstacles such as low mechanical properties, interfacial adhesion problems, and nonreusability hinder their rapid development. Here, an ionogel was developed by a one-step photopolymerization of an ionic liquid (IL) with the C═C bond of 1-vinyl-3-butylimidazolium tetrafluoroborate in another ionic liquid solution of 1-butyl-3-methylimidazolium tetrafluoroborate without a chemical cross-linker. The poly(ionic liquid) and the ionic liquid (PIL/IL) were highly compatible and resulted in an extremely uniform, stable, and optically transparent PIL/IL ionogel. In addition, this method also avoided complicated solvent replacement in the preparation processes of common ionogels. Our experimental and theoretical results showed that the reported ionogel integrated excellent mechanical properties, ultrastrong adhesive, self-healability, and recyclability. These remarkable advantages were benefited from the strong electrostatic force and other noncovalent bond interactions in the ionogel system. The unique ionogel presented in this study is therefore an ideal candidate material for self-adhesive and reusable wearable electronics.

Use of Surface Penetration Technology to Fabricate Superhydrophobic Multifunctional Strain Sensors with an Ultrawide Sensing Range.

Flexible sensors with wide sensing ranges require responsiveness under tiny and large strains. However, the development of strain sensors with wide detection ranges is still a great challenge due to the conflict between the tiny strain requirements of sparse conductive networks and the large strain requirement of dense conductive networks. Herein, we present a facile method for fabricating a gradient conductive network composed of sparse and dense conductive networks. The surface penetration technology in which carbon black (CB) penetrated from the natural rubber latex (NRL) glove surface to the interior was used to fabricate a gradient conductive network. The prolonged immersion time from 1 to 30 min caused the penetration depth of CB to increase from 2 to 80 μm. Moreover, CB formed hierarchical rough micro- and nanoscale structures, creating a superhydrophobic surface. The gradient conductive network of sensors produced an ultrawide detection range of strain (0.05-300%) and excellent reliability and reproducibility. The sensors can detect a wide range of human motions, from tiny (wrist pulse) to large (joint movements) motion monitoring. The flexible sensors attached to a flexible basement can be used to detect pressure in a wide detection range (1.7-2900 kPa). Pressure responsiveness was used to detect the weight, sound pressure, and dripping of tiny droplets. The sensor showed an excellent response to organic solvents, and the response intensity increased with the increasing swelling degree of the solvent for NRL.

Flexible, self-powered and multi-functional strain sensors comprising a hybrid of carbon nanocoils and conducting polymers

The development of flexible and stretchable multi-functional sensors addresses the requirements for applications in fields of electronic skins, artificial intelligence, and health/structure monitoring. Here, we fabricated a novel self-powered strain-temperature dual-functional sensor based on composite films of carbon nanocoils (CNCs) and a conductive elastomeric blends of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and waterborne polyurethane (WPU). Owing to the high stretchability of helical-structured CNCs, high elasticity of WPU and multiple interfacial contacts between the conducting constitutes, the sensor exhibited a broad strain detection range of 0–50% and a high sensitivity with gauge factor (GF) of 25. Based on the Seebeck effect arising from the conducting polymer of PEDOT:PSS, the sensor-enabled both detection of temperature changes and strain deformations at a self-powered circumstance. To demonstrate its practical application as a wearable device, the senor was directly attached to the human skin. It not only detected subtle human motion and strain stimuli but also could distinguish the stimuli from either a warm or a cold objective by telling the difference in their temperature signals. This is the first time that the CNC-based composites are developed for use as a multi-functional sensing medium. Our self-powered strain-temperature dual-functional sensor demonstrates great potential in flexible devices and e-skin applications.

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

Recent advances in the design and implementation of wearable resistive, capacitive, and optical strain sensors are summarized herein. Wearable and stretchable strain sensors have received extensive research interest due to their applications in personalized healthcare, human motion detection, human–machine interfaces, soft robotics, and beyond. The disconnection of overlapped nanomaterials, reversible opening/closing of microcracks in sensing films, and alteration of the tunneling resistance have been successfully adopted to develop high‐performance resistive‐type sensors. On the other hand, the sensing behavior of capacitive‐type and optical strain sensors is largely governed by their geometrical changes under stretching/releasing cycles. The sensor design parameters, including stretchability, sensitivity, linearity, hysteresis, and dynamic durability, are comprehensively discussed. Finally, the promising applications of wearable strain sensors are highlighted in detail. Although considerable progress has been made so far, wearable strain sensors are still in their prototype stage, and several challenges in the manufacturing of integrated and multifunctional strain sensors should be yet tackled.

Printed, Soft, Nanostructured Strain Sensors for Monitoring of Structural Health and Human Physiology.

Soft strain sensors that are mechanically flexible or stretchable are of significant interest in the fields of structural health monitoring, human physiology, and human-machine interfaces. However, existing deformable strain sensors still suffer from complex fabrication processes, poor reusability, limited adhesion strength, or structural rigidity. In this work, we introduce a versatile, high-throughput fabrication method of nanostructured, soft material-enabled, miniaturized strain sensors for both structural health monitoring and human physiology detection. Aerosol jet printing of polyimide and silver nanowires enables multifunctional strain sensors with tunable resistance and gauge factor. Experimental study of soft material compositions and multilayered structures of the strain sensor demonstrates the capabilities of strong adhesion and conformal lamination on different surfaces without the use of conventional fixtures and/or tapes. A two-axis, printed strain gauge enables the detection of force-induced strain changes on a curved stem valve for structural health management while offering reusability over 10 times without losing the sensing performance. Direct comparison with a commercial film sensor captures the advantages of the printed soft sensor in enhanced gauge factor and sensitivity. Another type of a stretchable strain sensor in skin-wearable applications demonstrates a highly sensitive monitoring of a subject's motion, pulse, and breathing, validated by comparing it with a clinical-grade system. Overall, the presented comprehensive study of materials, mechanics, printing-based fabrication, and interfacial adhesion shows a great potential of the printed soft strain sensor for applications in continuous structural health monitoring, human health detection, machine-interfacing systems, and environmental condition monitoring.

Self-Derived Superhydrophobic and Multifunctional Polymer Sponge Composite with Excellent Joule Heating and Photothermal Performance for Strain/Pressure Sensors.

Flexible strain or pressure sensors have potential applications in electronic skin, healthcare, etc. It remains a challenge to explore multifunctional strain or pressure sensors that possess excellent water repellent and heating performance and hence can be used in harsh environments such as high moisture and low-temperature conditions. Here, a self-derived superhydrophobic and multifunctional polymer composite foam is prepared by adsorption of the Ag precursor in tetrahydrofuran (THF) onto the rubber sponge followed by reduction of Ag+ to Ag nanoparticles (AgNPs). During the Ag+ reduction in hydrazine solution, the swollen rubber sponge by THF is partially precipitated based on the nonsolvent-induced phase separation (NIPS). The NIPS creates a porous structure on the sponge surface and thus a high surface roughness, contributing to the material superhydrophobicity. The precipitated polymer wrapping the AgNPs could enhance the interaction between the individual AgNPs. The obtained conductive sponge composite possesses excellent Joule heating and photothermal performance and can be used as both a strain and pressure sensor. The conductive sponge composite sensor possesses good reliability and durability and can be applied to real-time monitoring of human body movements.

Stretchable conductive Ni@Fe3O4@Polyester fabric strain sensor with negative resistance variation and electromagnetic interference shielding

Abstract Soft textile-based electronic devices are promising for the development of flexible strain sensors, and useful in the fields of manufacturing, smart robots, and wearable health monitoring. In this study, we fabricated a flexible, highly responsive, and electrically conductive hierarchical Ni@Fe3O4 textile strain sensor (Ni@PET-g-PAO/Fe3O4) by radiation-induced graft polymerization, in-situ formation of Fe3O4, and subsequent electroless deposition of nickel (Ni) on a polyester (PET) fabric. Compared with the previously reported strain sensors, our hierarchical strain sensor exhibited reveals a distinctive negative resistance variation and was an excellent stretchable conductor with the increase in strain. Fe3O4 acted as a joint component by improving the adhesion of the conductive Ni layer to the support and reducing the influence of the thermal deformation of the organic fiber on the sensitivity, while enhancing the magnetic properties of the Ni metal layer. This provided the multifunctional strain sensor with excellent robust performances. The strain sensor exhibited a fast and repeatable response and displayed long-term stability in the strain range of 0–40% and an operation frequency of 0.05–1 Hz. In addition, the strain sensor was used to detect and monitor finger bending, wrist twisting, and walking. Moreover, the strain sensor could be sewed into clothing to monitor human motions. In addition, the strain sensor exhibited excellent electromagnetic interference shielding efficiency and magnetic response. Therefore, this study provided a general and effective strategy to design smart wearable devices with high performances.

Multifunctional stretchable strain sensor based on polydopamine/ reduced graphene oxide/ electrospun thermoplastic polyurethane fibrous mats for human motion detection and environment monitoring

Various sensors have been developed to monitor the changes in physical quantities to meet the growing demand for wearable electronics. While it is still a huge challenge to design a multifunctional flexible sensor with both high strain responsivity and good breathability. In this work, through electrospinning, ultrasonication and in-situ polymerization of dopamine, we prepared a multifunctional strain sensor. We decorated polydopamine (PDA) onto the surface of reduced graphene oxide (RGO)/thermoplastic polyurethane (TPU) fibers. Here, PDA containing hydrophilic groups (-OH, –NH2) was used to improve the hydrophilic breathability of the membrane and prevent the RGO falling off from TPU fibrous mat. The PDA/RGO/TPU (PRT) fibrous strain sensor exhibits excellent comprehensive performance of excellent stretchability, good durability (stretching/releasing test of 9000 cycles under 50% strain), high sensitivity (gauge factor (GF) 23.2 within 60% strain, 185 towards 60%–100% strain), and fast response time (100 m s). Specially, owing to the introduction of PDA, the water vapor volatilization rate of our PRT strain sensor (38%) is almost the same as the blank control group (39%), indicating that our fibrous sensor has excellent breathability. In order to monitor various movements of human body parts (finger, wrist, elbow, and leg bending), our sensors were attached to volunteers' joints to monitor resistance changes in real time. In addition, our PRT fibrous mat also has excellent sensitive performances towards organic gases and humidity, showing its multifunctional ability for detecting various environment stimuli.

Ultrasensitive and Highly Stretchable Multifunctional Strain Sensors with Timbre‐Recognition Ability Based on Vertical Graphene

AbstractStretchable/wearable strain sensors are attracting growing interest due to their broad applications in physical and physiological measurements. However, the development of a multifunctional highly stretchable sensor satisfying the requirements of ultrahigh sensitivity (able to distinguish sound frequency) remains a challenge. An ultrasensitive and highly stretchable multifunctional strain sensor with timbre‐recognition ability based on high‐crack‐density vertical graphene (VGr) is fabricated using an ultrasonic peeling (UP) method. It can distinguish frequencies of sounds higher than 2500 Hz. Detailed microscopic examinations reveal that their ultrahigh sensitivity stems from the formation of high‐density nanocracks in the graphitic base layer, which is bridged by the top branched VGr nanowalls. These nanocracks cut the VGr film into a large number of nanopieces, which increase the natural frequency of the sensors, enabling the sensors to distinguish the sound frequency. Demonstrations are presented to highlight the sensors' potential as wearable devices for human physiological signal and timbre detections. This is the first multifunctional highly stretchable strain sensor with timbre‐recognition ability.

Graphene/Glycerin Solution-Based Multifunctional Stretchable Strain Sensor with Ultra-High Stretchability, Stability, and Sensitivity.

Highly stretchable, flexible, and sensitive strain sensors have promising applications in motion detection—especially multifunctional strain sensors that can detect stretching, bending, compression and twisting. Herein, this study presents a graphene and glycerol solution-based multifunctional sensor with ultra-high stretchability and sensitivity. Owing to the self-lubrication and fluidity of the graphene-glycerol solution, the strain sensors display super stretchability up to 1000%, a maximum gauge factor up to 45.13, and excellent durability for over 10,000 cycles. In addition, the sensor can also rapidly respond to small strains (1%, 5%, 10%) and different stretching rates (12.5%/s, 25%/s, 50%/s, and 100%/s). More impressively, the sensors can measure up to 50 kPa pressure and 180° twisting without any damage. Furthermore, the strain sensors demonstrate their applicability in scenarios involving motion detection, such as that for finger bending, wrist rotating, touching, and drinking water.