Multifunctional Strain Sensors Research Articles

Elastomeric Sensor-Triboelectric Nanogenerator Coupled System for Multimodal Strain Sensing and Organic Vapor Detection.

Stretchable, flexible sensors are one of the most critical components of smart wearable electronics and Internet of Things (IoT), thereby attracting multipronged research interest in the last decades. Following miniaturization and multicomponent development of several sensors in one could further propel the demand for wireless, multimodal platforms. Greener substitutes to conventional sensors that can operate in a self-powered configuration are highly desirable in terms of all-in-one sensor utilities. However, fabrication of composite-based ultrastretchable, self-powered sensors with multifunctionality, robustness, and conformability is still only partially achieved and, therefore, demands further investigation. In this work, we report a triboelectric nanogenerator (TENG)-based multifunctional strain and organic vapor sensor using cross-linked ethylene propylene diene monomer (EPDM) elastomer and conducting carbon black as active fillers in the presence of an ionic liquid. The resulting piezoresistive sensor demonstrates ultrahigh gauge factor (GF > 220k) and wide range strain sensitivity and is, therefore, suitable for subtle-to-high frequency motion detection devices. Supported by excellent triboelectric outputs (force sensitivity 0.5 V/N in the range of 50-300 N, maximum output voltage VOC ∼ 178 V, short circuit current ISC ∼ 18 μA, maximum power density 0.11 mW/cm2), the hybrid sensors offer remarkable mechanical toughness and seamless voltage generation under contact-separation, even after several thousand cycles of operations. Furthermore, the sensor substrates exhibited reproducible organic vapor-sensing behavior, with high responsivity of 1.92 and 1 for ethanol and acetone, respectively, under flowing vapor conditions. This work lays a strong foundation for developing a truly multimodal, TENG-based, self-powered organic vapor and strain sensors.

Multifunctional strain sensor with adjustable conductive network for wearable applications

AbstractWearable sensors based on nanomaterials have recently elicited keen research interest and potential for a new range of flexible devices. This paper presents a simple method for the preparation of laser‐induced porous graphene (LIG) and discusses its application in monitoring human vital signs. LIG formed on a polyimide (PI)/polydimethylsiloxane (PDMS) composite material exhibits inherent high stretchability (over 30%), eliminating the need for transfer processes used in LIG prepared by laser scribing on PI films. LIG/CuSO4 composite materials, with different concentrations of Cu particles, show tunable mechanical and electronic properties based on laser‐induced graphene. The fabricated LIG demonstrates good cyclic stability and a nearly linear resistance response to tensile strain, making it suitable for wearable electronic devices, the maximum strain value and linear response to applied strain from 3% to 79%. The sensor exhibits a fast response time and high sensitivity, enabling real‐time detection of human pulse, joint motion, and complex dynamics. The multifunctionality advantages of LIG flexible sensor offer potential applications in next‐generation wearable electronics.

Ultrasensitive, highly stretchable and multifunctional strain sensors based on scorpion-leg-inspired gradient crack arrays

Wearable flexible strain sensors based on conductive films have shown great application potential in many high-tech fields. They have high requirements for synergistic performances of sensitivity, flexibility, stability and durability. However, overcoming the trade-off between high sensitivity and high stretchability is still a great challenge in this research. Here we develop a facile strategy to prepare high-performance flexible strain sensors based on gradient crack arrays inspired by the gradient slits on scorpion legs. The gradient crack arrays with branched or hierarchical features controllably form in a periodic thickness-gradient metal film prepared by one-step masking technique on a flexible substrate. The cracks are progressively open from the thickest film region to the thinnest one under mechanical strain, behaving a unique sensing mechanism. As a result, the gradient crack-based strain sensors possess excellent comprehensive performances including high sensitivity (up to 21000), wide sensing range (∼70 %), low detection limit (0.02 %), quick response speed (below to 80 ms), excellent stability and durability (up to 15,000 cycles at 5 % strain). As demonstration of applications, the sensors are used to monitor various human activities and to express and encrypt information by bending bidirectionally. This work provides a novel way to fabricate highly sensitive, stretchable, robust, multifunctional, crack-based flexible strain sensors, which would greatly expand the applications in flexible electronics and wearable devices.

Flexible and self-healing tannic acid-Fe3O4@MXene-composited dual network hydrogel multifunctional strain sensor

In light of the exponential growth of flexible human-computer interactions and telecommunications, it is becoming increasingly important to develop a high-sensitivity strain sensor to monitor human movement. Herein, the biocompatible, adhesive, and flexible Tannic acid-Fe3O4@MXene-poly(methacryloxyethyl sulfobetaine/acrylamide) (TFM) hydrogel has been prepared to realize the dual-functional applications in strain sensitive sensor and electromagnetic interference (EMI) shielding. The polymer network and 2D conductive filler MXene together construct the conductive network inside the hydrogel. The interpenetrating network and hydrogen bond between poly(acrylamide) and poly(methacryloxyethyl sulfobetaine) chain enhance the mechanical property of hydrogel, which is also improved by the complexation between Fe3O4 and the catechol groups of tannic acid. Benefiting from the excellent electrical conductivity (∼1.33 S/m) and mechanical property of the TFM hydrogels, the strain sensor displays compressive strain (∼77.6 %) and elongation (∼308.5 %), adhesion (∼16 kPa), compression sensitivity (∼42.6 Pa−1), gauge factor (GF = 2.38), and cyclic stability (∼50 cycles). TFM hydrogels can monitor strain distribution sensing, pulse beating and human movement detection. Moreover, the TFM hydrogel exhibits an absorption-predominant EMI shielding performance with an effective value of ∼25.2 dB. This work provides a new inspiration for the development of multifunctional hydrogels in the fields of artificial intelligence, human-computer interaction, and EMI shielding technology.

4D printed multifunctional wearable strain sensors with programmable sensing characteristics

Combining 4D-printed bilayer actuators with the slit structure and sensing capabilities unique to the process further promotes the use of 4D printing in biomedical devices, human-computer interaction, intelligent self-protection devices, and humanoid robots. In this study, we propose an adaptive multifunctional strain sensor (AMSS) 4D printing strategy based on the shape memory properties of polylactic acid (PLA), a bioslit structural sensing unit, and a bi-directional deformation design of a bilayer structure. The obtained AMSS was shown to have excellence sensitivity to strain, mechanical, and temperature stimuli. In particular, thanks to the 3D printed slit structure and phase transition properties of the PLA printing layer, the AMSS macro-microstructure can be precisely tuned, and its sensing performance is shown to be intelligently programmable. The built-in structural design-induced macro-deformation enables AMSS to adaptively fit human joint surfaces for full-range human motion recognition. In addition, the close correlation of strain-sensing during AMSS shape transformation enables position self-sensing and strain self-sensing of AMSS. Further, through the integration and separation of resistive signals, we are able to recognize temperature and mechanical stimuli. Finally, we integrate the wireless sensing module into the AMSS to improve the portability and wearability of the sensor.

Flexible and breathable textile-based multi-functional strain sensor for compressive sensing, electromagnetic shielding, and electrical heating

The textile-based sensors have drawn increasing attention in wearable smart electronics, owing to the comfort, breathability, and elasticity. However, the low compressive strain response range, poor thermal comfort and electromagnetic shielding performance hinder severely the application of textile-based sensors in the complex environments. To address these issues, we chose a weft-flat knitted textile with a large gap as a flexible substance, graphene nanosheets (GNS), and Ag nanowires (Ag NWs) as conductive fillers, and treated the textile with a simple dip coating strategy to obtain TPU/GNS/Ag NWs@textile (TAG@textile). The prepared TAG@textile sensor not only exhibits 90% compressive strain response range and high sensitivity (GF=9.25), but also exhibits an efficient electromagnetic shielding performance of 61.68 dB. In addition, the TAG@textile sensor has excellent Joule thermal performance (it can reach 104 °C at a low voltage of 4 V). In brief, this work integrates human motion detection, electromagnetic shielding, and electrical heating, showing a great potential in future multifunctional wearable electronic devices.

Highly Sensitive and Wide Detection Range Thermoplastic Polyurethane/Graphene Nanoplatelets Multifunctional Strain Sensor with a Porous and Crimped Network Structure.

High-performance flexible strain sensors have tremendous potential applications in wearable devices and health monitoring. However, developing a flexible strain sensor with high sensitivity over a wide strain range remains a significant challenge. In this study, a fibrous membrane with a porous and crimped structure was designed as the substrate material for TPU/GNPs flexible strain sensors. This structural design effectively balances sensitivity with the strain range. The TPU-PEO fibrous membrane prepared using electrospinning with water washing, resulted in a porous fibrous membrane with a TPU framework. Subsequently, the fibrous membrane was subjected to anhydrous ethanol stimulation to obtain a porous and crimped network structure. GNPs were modified on the TPU fibrous membrane through ultrasonic treatment. The produced flexible strain sensor exhibited high sensitivity (GF = 4047.5) within a large strain range (350%) and demonstrated excellent sensing performance, stability, and durability (>10,000 cycles). It not only captured basic movements but also efficiently recognized and measured bending angles, enabling a more sophisticated human-machine interaction experience. This advancement opens up possibilities for future intelligent wearable technology and human-machine interaction, contributing to the evolution of these fields.

A multifunctional wearable electronic skin: Wide range temperature sensing based on copper nanoclusters organo-hydrogel with self-healable, self-adhesive, anti-freezing properties

The use of extremely accurate, simple-to-use, flexible, and biocompatible wearable electronics for temperature monitoring is of great clinical demand for COVID-19 cases, postoperative recovery, monitoring chronobiology, and disease prediction. To address these issues, we report the fabrication of wearable three-dimensional (3D) Polydopamine titanium dioxide copper nanocluster (PDA-TiO2@Cu-NCs) sensor based on cost effective copper nanoclusters (Cu-NCs). The results reveal that the developed multi-functional strain sensor demonstrated biocompatibility, environmental stability, flexible thermistor with ultra-sensitivity. The sensor was used to detect wide human physiological activities with superior sensitivity of 177 % for finger bending angle 0° to 90° and 1770 % for compressed by human leg with higher stability and fast recovery 20 ms. The smart sensor monitored human respiration patterns and could identify people by facial recognition and handwriting sensory device. Additionally, the proposed thermistors sensor can detect wide temperature range changes in two different rang with a temperature coefficient of resistance (TCR) value of –0.143 °C−1 at 0 °C to 60 °C with high resolution of 2 °C. This research provides a new high-performance multifunctional sensor design for potential applications as flexible electronics, human body temperature sensors, thermistors, photodetector, anti-counterfeiting, and medical diagnostics related applications.

Multifunctional visualized electronic skin based on a solvatochromic poly (ionic liquid) ionogel

The biological skins exhibit various fascinating visual functions, such as turning red in response to strain, whitening upon hydrogen peroxide stimulation, and changing color in accordance with the environment (octopus). Inspired by these phenomena, two kinds of multifunctional visualized electronic skin (e-skin) were designed and fabricated based on a novel poly (ionic liquid) ionogel. Herein, we reported a transparent and conductive poly (ionic liquid) ionogel (P(AAm-IL)) by photopolymerizing acrylamide (AAm) with 1-vinyl-3-butylimidazolium tetrafluoroborate (ionic liquid, IL) in ethylene glycol (EG). Interestingly, P(AAm-IL) displays a solvatochromic phenomenon, and typical hydrogen-bonding acceptor solvents like acetone, methanol, and nitromethane induce a whitening effect in it. Based on this ionogel, we fabricated multifunctional strain sensors integrated with the visualized chemical sensing ability. The discoloration mechanism of the chemical sensing was detailed studied. Furthermore, by combining the P(AAm-IL) ionogel with Lithium trifluoroethane sulfonate (LiTf), the blend P(AAm-IL)-Li ionogel exhibits enhanced stretchability (>4300 %), higher conductivity (1.44 × 10−2 S·m−1), good transparency (>80 %) as well as wide operating temperature range (−20 to 80 °C). A sandwich-structured e-skin (Polypyrrole/PAAm-IL-Li/CsPbBr3-TPU) exhibiting both electro-optical dual response to strain was successfully fabricated. The luminescent e-skin not only exhibits highly sensitive electrical responses but also demonstrates visible fluorescence changes in response to external strain variations. These multifunctional visualized e-skins demonstrate great potential for applications in chemical environmental monitoring robotics, wearable electronic devices, and human–computer interaction.

Rapid Radiation Synthesis of a Flexible, Self-Healing, and Adhesive Ionogel with Environmental Tolerance for Multifunctional Strain Sensors.

Ionogels are increasingly used in flexible strain sensors, but it is still challenging to incorporate multifunctional properties such as flexibility, self-healing, adhesion, temperature resistance, and electrical conductivity. Herein, a facile and rapid one-step photoinitiated polymerization strategy is employed to prepare multifunctional ionogels by filling a hydrophobic and conductive ionic liquid into a flexible, hydrophobic fluoropolymer matrix. Thanks to the presence of abundant noncovalent interactions (hydrogen-bonding and ion-dipole interactions), the ionogels exhibit high transparency, excellent mechanical properties, self-healing ability, and adhesion. Moreover, rich C-F bonds in the fluoropolymer matrix can eliminate the interference of water molecules, resulting in excellent environmental tolerance such as high and low temperature resistance, waterproofness, and anticorrosion. Furthermore, the ionogel-based wearable strain sensor can sensitively detect and differentiate human movements and subtle muscle movements and serve as a Morse code signal transmitter for information transmission. The presented work provides an effective method to develop versatile flexible conductive ionogels for wearable devices and ionotronics.

3D printed mechanical robust cellulose derived liquid-free ionic conductive elastomer for multifunctional electronic devices

Ionic gel-based wearable electronic devices with robust sensing performance have gained extensive attention. However, the development of mechanical robustness, high conductivity, and customizable bio-based ionic gel for multifunctional wearable sensors still is a challenge. Herein, we first report the preparation of 3D printed cellulose derived ionic conductive elastomers (ICEs) with high mechanical toughness, high conductivity, and excellent environment stability through one-step photo-polymerization of polymerizable deep eutectic solvents. In the ICEs, carboxylate cellulose nanocrystals (C-CNCs) were used as a bio-template for the in-situ polymerization of the aniline to avoid the aggregation of polyaniline and yield a high conductivity (58.7 mS/m). More importantly, the well-defined structural design combining multiple hydrogen bonds with strong coordination bonds endows the ICEs with extremely high mechanical strength (4.4 MPa), toughness (13.33 MJ*m−3), high elasticity and excellent environment stability. Given by these features, the ICE was utilized to assemble multifunctional strain, humidity, and temperature sensors for real-time and reliable detection the human motions, respiration, and body temperature. This work provides a promising strategy for designing the new generation of strong, tough bio-based ionic gel for multifunctional wearable electronic devices.

Highly stretchable, self-healing, self-adhesive and conductive nanocomposite hydrogels based on multi-reversible interactions as multifunctional strain sensors

Construction of highly stretchable and sensitive flexible strain sensors is of great significance for wide applications in human–computer interaction, wearable devices, and electronic skins. However, it turned out to be not effortless to integrate the two seemingly contrary features of high stretchability and sensitivity into a system. Herein, we designed a nanocomposite conductive hydrogel (NCCH) composed of zwitterionic poly(HEAA-co-SBMA) polymers and lithium magnesium silicate (XLG) by means of multi-reversible molecular interactions (MRMIs) including borate ester bonds between polyHEAA and borax, hydrogen bonds, and polySBMA-XLG-based electrostatic interaction, endowing the NCCH with enhanced mechanical, self-healing, adhesive, biocompatible, and sensing performances. The MRMI method enabled NCCHs to obtain an excellent stretchability (∼1080 %)/compressibility (∼98.5 %), a tensile strength of ∼ 0.06 MPa, a good self-healing with a fracture strain recovery of 90.5 %, and a strong adhesion on various hard and soft substrates (e.g. a adhesive shear force of 60 kPa to pigskin tissues). Besides, the integration of zwitterionic polySBMA and conductive XLG promoted charge transfer.by optimal ioinic channels. Based on these outstanding strengths, the NCCHs were farther rationally fabricated as multifunctional strain sensors with remarkable sensing stability for fast and accurately detecting strain/pressure-induced deformation, joint motions, and animal heartbeats. Notably, the excellent self-healing property of NCCH sensors can facilitate their long-period usage and complete recyclability for avoiding wastes. The new MRMI-based NCCH sensor without any conductive additives is deemed to provide a new strategy for broadening their multifunctional strain sensor and healthcare monitoring applications.

Ion-based double network hydrogel with compressive, conductive, and sensing properties for sports monitoring

Conductive hydrogel, as a promising candidate material, is ideal for multifunctional strain sensors due to its similarity to biological tissues. It offers good wearability and high-precision information acquisition. However, fabricating conductive hydrogel-based strain sensors with both superior mechanical and conductive properties remains challenging. In this study, a compressive and conductive strain sensor based on multi-dynamic interactions is fabricated through a simple strategy. The strategy exploits hydrogen bonding and ionic ligand bonding by using nanocellulose reinforced poly(acrylic acid) hydrogels impregnated with the Fe3+ solution to prepare a double-network hydrogel. The prepared PAA/CNF–Fe3+ double-network hydrogel exhibited excellent properties, including extraordinary performance compressive stress (2.96 MPa) and remarkable electrical conductivity (6.34 S/m). With these advantages, the PAA/CNF–Fe3+ double network hydrogel was developed to be an attractive strain flexible sensor with cyclic stability (150 cycles) and good strain sensitivity (GF = 2.87). In addition, the PAA/CNF–Fe3+ hydrogel flexible sensor can be used as an electronic skin to accurately discriminate subtle and large body movements. Given the simple strategy, double network structure, and satisfactory functionality, the PAA/CNF–Fe3+ hydrogel provides a new sustainable and multifunctional development strategy that can be applied in the field of strain sensors and medical detection.

Hofmeister effect-inspired Ti3C2Tx MXene-based robust, multifunctional hydrogels

Developing multifunctional hydrogels with high strength, toughness, and conductivity is critical for various applications in soft robots, wearable devices, and human–computer interfaces. Inspired by the Hofmeister effect, a type of composite hydrogels was prepared using a freezing and salting-out approach, which combines transition metal carbide/nitride (MXene) and polyvinyl alcohol (PVA). The hydrogels exhibited great mechanical strength and toughness, and high conductivity, conferring its application as a multifunctional strain sensor. In addition, the synergy of highly conductive MXene, water-enriched porous structure, and sufficient MXene-PVA interfaces contributes to the controllable and high electromagnetic interference shielding effectiveness of 43–93 dB at thickness of 1.5–8.5 mm. Combined with the facile and scalable preparation approach for rational design of the MXene, PVA, water, and porous structure in the hydrogels, this work thus demonstrates the robust, ultra-flexible and electrically conductive multifunctional hydrogels for applications in Internet of Things, next-generation wearable electronics, electromagnetic protection, and smart devices.

Radiation synthesis of rapidly self-healing, durable, and flexible poly(ionic liquid)/MXene gels with anti-freezing property for multi-functional strain sensors

As a new type of flexible electronic materials, conductive gels have attracted considerable interest because of their distinctive physical and chemical properties. In this work, the ILs with -C=C- double bond function as monomer and crosslinker, respectively; while the two-dimensional (2D) transition metal carbides/nitrides (Ti3C2Tx MXene) functioned simultaneously as a “crosslinker” and nanofiller, then a series of new poly(ionic liquid)/MXene (Cn-PIL/MXene) gels with stable covalent and non-covalent cross-linking structures based on n-alkyl-imidazolium (n = 2, 8) ionic liquid and MXene are fabricated by a one-step radiation method. The results reveal that the gel containing shorter alkyl (C2-PIL/MXene) is more suitable for flexible materials. Additionally, the C2-PIL/MXene gel exhibits remarkable stretchability (nearly 600%), good conductivity (4.9 mS cm−1), rapidly self-healing ability (within 8 min), excellent adhesion (266.9 kPa), and a fast response time (within 100 ms) due to the stable covalent bonding and abundant hydrogen bonding in the gel network. Notably, the C2-PIL/MXene gel also shows an excellent anti-freezing property (−60 °C), excellent durability (90 days at room temperature), and outstanding antibacterial activity against E. coli (99.82%) and S. aureus (99.98%). In addition, the multi-functional sensor based on the C2-PIL/MXene gel exhibits a real-time and rapid response to detect various human activities, recognize writing strokes, and realize the encrypted transmission of information, thus showing considerable potential in flexible smart wearable devices.

Highly Elastic, Self-Healing, Recyclable Interlocking Double-Network Liquid-Free Ionic Conductive Elastomers via Facile Fabrication for Wearable Strain Sensors.

Liquid-free ionic conductive elastomers (ICEs) are ideal materials for wearable strain sensors in increasingly flexible electronic devices. However, developing recyclable ICEs with high elasticity, self-healability, and recyclability is still a great challenge. In this study, we fabricated a series of novel ICEs by in situ polymerization of lipoic acid (LA) in poly(acrylic acid) (PAA) solution and cross-linking by coordination bonding and hydrogen bonding. One of the obtained dynamically cross-linked interlocking double-network ICEs, PLA-PAA4-1% ICE, showed excellent mechanical properties, with high elasticity (90%) and stretchability (610%), as well as rapid self-healability (mechanical self-healing within 2 h and electrical recovery within 0.3 s). The PLA-PAA4-1% ICE was used as a strain sensor and possessed excellent linear sensitivity and highly cyclic stability, effectively monitoring diverse human motions with both stretched and compressed deformations. Notably, the PLA-PAA4-1% ICE can be fully recycled and reused as a new strain sensor without any structure change or degradation in performance. This work provided a viable path to fabricate conductive materials by solving the two contradictions of high mechanical property and self-healability, and structure stability and recyclability. We believe that the superior overall performance and feasible fabrication make the developed PLA-PAA4-1% ICE hold great promise as a multifunctional strain sensor for practical applications in flexible wearable electronic devices and humanoid robotics.

Hydrophobic and multifunctional strain, pressure and temperature sensor based on TPU/SiO2-ILs ionogel for human motion monitoring, liquid drop monitoring, underwater applications

Ionogel-based flexible electronic devices have attracted extensive attention from industry and academia due to their unique advantages in wearable electronic devices, human motion sensing, etc. However, the internal ionic liquids (ILs) or polymers have weak resistance to liquid interference, which limits the development of ionogel in the actual environment. In this paper, TPU/SiO2-ILs (Thermoplastic polyurethane/SiO2-Ionic liquids) ionogel with micro-nano structures on the surface was constructed by sandpaper template method and further modified by 1 H, 1 H, 2 H, 2 H-perfluorooctyltrichlorosilane to enhance its hydrophobicity. The ionogel sensor has a high sensitivity, a fast strain response time (346 ms), and excellent mechanical properties. In addition, the sensor can still show a stable response signal after 1000 s of strain and compression cycle testing. The ionogel sensor’s excellent hydrophobic properties allow it to be used not only in wearable electronic devices to detect human physiological activity in dry or underwater environments and for writing recognition systems, but also to monitor tiny response signals caused by toy fish wiggling and droplet dripping. Most importantly, compared with other sensors that can only monitor a single stimulus, the TPU/SiO2-ILs ionogel sensor has a wide and multifunctional detection range for stimuli in different environmental such as strain (0.1–200%), pressure (0.6–25 kPa) and temperature (30–100 °C). Thus, the TPU/SiO2-ILs ionogel shows great potential for applications in areas such as smart electronic skin, human motion monitoring, underwater communication and underwater environmental monitoring.

A supersensitive wearable sensor constructed with PDMS porous foam and multi-integrated conductive pathways structure

In recent years, wearable multifunctional strain sensors have attracted attention for their promising applications in wearable electronics and portable devices. To achieve a high-performance wearable strain sensor with a wide sensing range and high gauge factor (GF), wisely choosing appropriate conductive materials and a rational structural design is essential. Herein, we develop a supersensitive sensor that contains one-dimensional conductive material CNT and two-dimensional material MXene built on a PDMS porous foam that is made based on a sugar template. The one-dimensional carbon nanotube (CNT) functionalizes as a conductive scale layer through solvent swelling and evaporation on the surface of the PDMS skeleton. The two-dimensional MXene is applied on top of the CNT layer to form final conductive pathways. The PDMS/CNT@MXene (PCM) sensor has a wide sensing range (150%), high sensitivity (GF = 26438), rapid response speed (response/recovery time of 60/71 ms), and exceptional durability (>1000 cycles) owing to its unique porous structure with scale layers and graded fracture of conductive pathways. Moreover, the PCM sensor is capable of monitoring subtle and significant human activities and is used for wireless sensing and medical diagnostics, even for solvent identification. The superior performance of the PCM sensor provides vast application potential in human movement, health monitoring, and warning devices.

Flexible assembled tactile sensor with freely integration design

Flexible touch-sensing devices have become increasingly multifunctional in wearable interaction electronics owing to the diversification of material synthesis and the flexibility in the structure design. Especially, the latter provides capabilities for the existing sensors owning the common materials with new possibilities to acquire certain requisite functions. Herein, we designed a strain sensor by assembling the nature rubber (NR) substrate with the MoS2/MWCNT conducting network structure. For demonstrating the flexibility of the proposed integrated model under the application of NR, practical applications were exhibited. The bendable biomimetic hair sensor is integrated into the smart car for robotic tactile to imitate the manner of mammals when sensing the surroundings. Besides, a flexible sensing array can be designed into arbitrary shapes according to users’ requirements manifesting its flexibility and practicability. What is more, the sensor used as electronic skin (e-skin) can realize tactile sensing and meanwhile monitor human body movements. The success of this study paves the way for extending this technology to tactile sensing which is a promising lead to develop multifunctional strain sensors for widespread applications.

Design and evaluation of 3D-printed auxetic structures coated by CWPU/graphene as strain sensor

A strain sensor characterized by elasticity has recently been studied in various ways to be applied to monitoring humans or robots. Here, 4 types of 3D-printed auxetic lattice structures using thermoplastic polyurethane as raw material were characterized: truss and honeycomb with positive Poisson's ratio and chiral truss and re-entrant with negative Poisson's ratio. Each structure was fabricated as a flexible and stable strain sensor by coating graphene through a dip-coating process. The fabricated auxetic structures have excellent strength, flexibility, and electrical conductivity desirable for a strain sensor and detect a constant change in resistance at a given strain. The 3D-printed auxetic lattice 4 type structures coated with CWPU/Graphene suggest potential applications of multifunctional strain sensors under deformation.