Wrist Bending Research Articles

High-Performance Flexible Pressure Sensor with Micropyramid Structure for Human Motion Signal Detection and Electromagnetic Interference Shielding.

Flexible pressure sensors have a wide range of applications in the field of human motion signal detection, but the electromagnetic radiation generated during the monitoring process has become an unavoidable problem. Nowadays, it is still a challenge to develop high-performance pressure sensors with excellent electromagnetic interference (EMI) shielding performance. Herein, the Ti3C2TX MXene/carbon fiber/multiwalled carbon nanotube/polydimethylsiloxane (MXene/CMP) films with a micropyramidal structure were developed by the technology of vacuum high-temperature hot pressing and spray deposition. Benefiting from the dielectric loss of the conductive fillers and the presence of the microstructure, the MXene/CMP film exhibits excellent EMI shielding performance, and the EMI shielding efficiency (SE) can reach 49.37 dB. Besides, the introduction of CF effectively improves the mechanical properties of the MXene/CMP films, and the MXene nanosheets deposited on the surface of the film can reduce stress concentration, which in turn delays the expansion of cracks. Furthermore, the MXene/CMP sensor exhibits high sensitivity (89.76 kPa-1) and fast response/recovery time (61/60 ms). The deformation of microstructure and the construction of conductive networks enable the sensor to realize the monitoring of human motion signals (such as finger bending, knee bending, wrist bending, etc.). Meanwhile, the sensor maintains sensing stability even after 2000 pressure cycles, which can be attributed to the improvement in mechanical properties. In summary, the developed high-performance flexible pressure sensor with micropyramid structure has great application prospects in wearable devices and healthcare.

Dual‐active‐layer flexible piezoresistive sensor based on wrinkled microstructures and electrospun fiber network for human‐related motion sensing applications

AbstractFlexible pressure sensors with high sensitivity and a wide detection range must be developed for practical applications. In this study, a dual‐active‐layer flexible piezoresistive sensor was developed. A reduced graphene oxide film with wrinkled microstructures was prepared by a simple and low‐cost substrate pre‐stretching method and used as the first active layer. A thermoplastic polyurethane electrospun fiber membrane was modified by fast polydopamine coating and ultrasonication with multi‐walled carbon nanotubes and used as the second active layer. Owing to the continuously changing conductive pathways created by the wrinkled microstructures and fiber network under pressure deformation, the sensor achieved a detection range of 0–100 kPa, with sensitivities of 8.5, 1.35, and 0.39 kPa−1 in the ranges of 0–1, 1–20, and 20–100 kPa, respectively. Additionally, the sensor exhibited a low detection limit (2 Pa), response and recovery times of 105 and 85 ms, respectively, and reliable service performance over 10,000 loading/unloading cycles. The sensor enabled real‐time monitoring of finger and wrist bending, beaker‐holding, and fingertip‐sliding on a touch screen, demonstrating its feasible applications in wearable electronics and human–machine interface devices.

Gallic acid melanin pigment hydrogel as a flexible macromolecule for articular motion sensing

In this study, water-soluble melanin was synthesized through the genetic recombination of Escherichia coli using gallic acid as a substrate. The recombinant host produced 2.83 g/L of gallic acid-based melanin (GA melanin) from 20 mM gallic acid. Notably, the isolated GA melanin demonstrated exceptional antioxidant and antimicrobial activities, exhibiting a 25.7 % inhibition ratio against Candida albicans. The structure and composition of GA melanin were analyzed using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD). Remarkably, GA melanin displayed high thermal stability, maintaining integrity up to 1000 °C. Additionally, it exhibited unique electrical properties in terms of conductivity and resistivity compared to other common types of melanin. Subsequently, GA melanin was cross-linked with hydrogel to create a sensing template. The resulting GA melanin hydrogel demonstrated lower resistance (80.08 ± 3.0 kohm) compared to conventional hydrogels (108.62 ± 10.4 kohm), indicating an approximately 1.77-fold improvement in adhesion. Given its physical, biological, and electrical properties, the GA melanin hydrogel was further utilized as a flexible motion-sensing material to detect resistivity changes induced by knee, wrist, and finger bending, as well as vocal cord vibrations. In all cases, the sensing module displayed notable sensitivity to motion-induced resistivity variations.

Synthesis of Self‐Adhesive, Self‐Healing and Antifreeze Conductive Hydrogels for Flexible Strain sensors

Abstract Recently, significant progress has been made regarding conductive hydrogels‐based flexible sensors in health detection, electronic skin, soft robots, etc. However, the requirement of bonding with the substrate through the adhesive tape, brokenness sensitivity, and degradation of performance under low‐temperature environments, strongly limit the wide applications of conductive hydrogels in flexible sensors. To solve these problems, this study introduces lithium chloride (LiCl) into poly(vinyl alcohol)/tannic acid/polyacrylamide (PVA/TA/PAM) hydrogels to endow the hydrogels with excellent conductivity and antifreeze properties. In addition, the addition of tannic acid (TA) and zwitterionic 3‐[Dimethyl‐[2‐(2‐methylprop‐2‐enoyloxy)ethyl]azaniumyl]propane‐1‐sulfonate (SBMA) enables the hydrogel to have good self‐healing performance (after 72 h of healing at 20 °C, the healing efficiency of fracture stress is 24%, and the healing efficiency of fracture strain is 52%) and adhesion (the adhesion strength to paper at 20 °C is 14.12 KPa). The sensors based on PVA/TA/PAM composite hydrogels exhibit good sensibility, stability, and durability, and can respond quickly to human joint activities (finger bending, wrist bending, arm bending, and leg bending). Therefore, the multifunctional PVA/TA/PAM composite hydrogel demonstrates significant potential for applications in flexible strain sensors under extreme environments.

Highly conductive copper-coated polyamide yarn for wearable sensing and Joule heating applications

A highly conductive yarn was developed by electroless deposition of copper metal particles on the polyamide 6 yarn. The successful incorporation of Cu particles into the substrate was revealed by surface and elemental characterizations. The Cu/PA 6 yarn exhibited superior electrical conductivity (2.3 Ω/cm) with improved mechanical properties. The excellent electromechanical properties demonstrated by the Cu/PA 6 composite revealed its sensing capacity for a wide range of strains. Therefore, the composite yarn was affixed to the different regions of the human body and was capable of successfully monitoring various human motions, including finger bending, wrist bending, knee bending, drinking, and writing. In addition, rapid heat generation with high and uniform surface temperature (66.3 °C at 4.0 V in 45 s) validated the potential of the Cu/PA 6 yarn for wearable thermal heating devices. Moreover, rapid heating at a lower voltage, when attached to a wristband, revealed the capability of the composite yarn for localized heating or region-specific temperature regulation for personalized healthcare or comfort. This study informs a facile and effective strategy for developing robust yarn-shaped e-textiles for advanced wearable sensing and thermal heating.

Highly-sensitive ultrathin flexible pressure sensor based on quasi-2D conductive network for human physiological signal monitoring

Ultrathin flexible pressure sensors are highly desirable for human physiological signal monitoring due to their portability and ability to conform to the body. However, existing ultrathin pressure sensors face challenges in balancing the sensitivity and their range. A spatial-dimensionally constrained strategy was proposed to construct an ultrathin active layer. In detail, multi-walled carbon nanotubes (MWCNTs) with an average length of ∼1.3 μm were intentionally spin-coated into a thin thermoplastic polyurethane (TPU) film with a thickness of 1.5 μm. By doing so, a quasi-2D MWCNTs conductive network is constructed, which enabled the sensor to have ultrahigh sensitivity of 27.04 kPa−1, a wide liner detection range of 0.2–24 kPa, ultrafast response time of 40 ms and a recovery time of 10 ms, and high durability in 1500 cycles under 0.2 kPa with loading/unloading frequency of 2 Hz. Thanks to this superior performance, the ultrathin pressure sensor can be used to monitor human movement and physiological signals, including finger touch, finger bending, wrist bending, and deep breathing. Moreover, the sensor can be attached to the side wall of the tip of the renal ureteroscope, allowing for the monitoring of renal pelvic pressure. Therefore, this spatial-dimensionally constrained strategy will open up a new way to fabricate highly sensitive ultrathin pressure sensors and have great application prospects in health monitoring.

Integrating High-Performance Flexible Wires with Strain Sensors for Wearable Human Motion Detection.

Flexible electronics have revolutionized the field by overcoming the rigid limitations of traditional devices, offering superior flexibility and adaptability. Conductive ink performance is crucial, directly impacting the stability of flexible electronics. While metal filler-based inks exhibit excellent conductivity, they often lack mechanical stability. To address this challenge, we present a novel conductive ink utilizing a ternary composite filler system: liquid metal and two micron-sized silver morphologies (particles and flakes). We systematically investigated the influence of filler type, mass ratio, and sintering process parameters on the composite ink's conductivity and mechanical stability. Our results demonstrate that flexible wires fabricated with the liquid metal/micron silver particle/micron silver flake composite filler exhibit remarkable conductivity and exceptional bending stability. Interestingly, increasing the liquid metal content results in a trade-off, compromising conductivity while enhancing mechanical performance. After enduring 5000 bending cycles, the resistance change in wires formulated with a 4:1 mass ratio of micron silver particles to flakes is only half that of wires with a 1:1 ratio. This study further investigates the mechanism governing resistance variations during flexible wire bending. Additionally, we observed a positive correlation between sintering temperature and pressure with the conductivity of flexible wires. The significance of the sintering parameters on conductivity follows a descending order: sintering temperature, sintering pressure, and sintering time. Finally, we demonstrate the practical application of this technology by integrating the composite ink-based flexible wires with conductive polymer-based strain sensors. This combination successfully achieved the detection of human movements, including finger and wrist bending.

Piezoelectric nanogenerator enabled fully self-powered instantaneous wireless sensor system

Self-powered real-time wireless sensor networks (WSNs) are vital for smart manufacturing, intelligent healthcare, and smart cities etc. Various nanogenerators have extensively exploited for powering these systems. Compared with triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs) have smaller dimensions and can be easier to integrate into ICs, offering broader applications. However, fully self-powered instantaneous wireless sensor systems with PENGs are yet to be realized. Here, we present a PENG based, self-powered, instantaneous wireless (PSIW) sensor system. The integration of the PENG with an RLC sensing circuit facilitates the spontaneous generation of oscillating signals with encoded sensing information. To address the high internal impedance issue of PENGs, a piezoelectric voltage driven electronic switch is employed, ensuring that the oscillating signal's frequency and amplitude remain highly stable. The effects of variables on signal frequency are investigated in detail. The sensor system is utilized to sense bending (strain), and to monitor physical actions such as elbow swing, wrist bending, walking, running etc. Results showed that the PSIW sensor system can effectively monitor strain and bending angles, and judiciously detect body’s physical movements. By employing either frequency-based or amplitude-based sensing methods, the PSIW sensor system demonstrates versatility and adaptability for various sensing applications.

High Performance Piezoelectric Nanogenerators Based on Polyvinylidene Fluoride-Graphene Nanoribbon Composite Thin Films.

In this study, a highly efficient, sensitive, and lightweight piezoelectric nanogenerator (PENG) is developed using graphene nanoribbons (GNRs) incorporated into the polyvinylidene fluoride (PVDF) matrix. Unzipping multi-walled carbon nanotubes is an effective and scalable strategy for synthesizing graphene nanoribbons. The synthesized GNRs are employed to prepare nanometer-scale piezoelectric polymer composite films showing higher piezoelectric performance than neat PVDF. The impact of GNR concentration in the PVDF matrix on the electroactive phase content and piezoelectric properties of the composites is systematically investigated. X-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR) analysis demonstrate an increase in the electroactive β and γ phases of PVDF by incorporating GNRs in the composites. With the optimized concentration of GNRs (1 wt%), the fabricated piezoelectric device can generate open-circuit voltage and an output power density of 26V and 16.52 µWcm2, respectively. It is also found that the PVDF-GNR 1 nanogenerator can be used to generate electrical power by converting mechanical energy from different human activities such as wrist bending, palm tapping, and toe tapping. The findings indicate that (PVDF-GNR 1) PENGcan be applied in self-powered portable and wearable electronic devices.

Biodegradable poly(lactic acid) blocked polyurethane/carbon nanotubes coated cotton fabric prepared by ultrasonic-assisted inkjet printing for high performance strain sensors

In order to fulfill the demands for degradability, a broad working range, and heightened sensitivity in flexible sensors, biodegradable polyurethane (BTPU) was synthesized and combined with CNTs to produce BTPU/CNTs coated cotton fabric using an ultrasonic-assisted inkjet printing process. The synthesized BTPU displayed a capacity for degradation in a phosphate buffered saline solution, resulting in a weight loss of 25 % after 12 weeks of degradation. The BTPU/CNTs coated cotton fabric sensor achieved an extensive strain sensing range of 0–137.5 %, characterized by high linearity and a notable sensitivity (gauge factor (GF) of 126.8). Notably, it demonstrated a low strain detection limit (1 %), rapid response (within 280 ms), and robust durability, enabling precise monitoring of both large and subtle human body movements such as finger, wrist, neck, and knee bending, as well as swallowing. Moreover, the BTPU/CNTs coated cotton fabric exhibited favorable biocompatibility with human epidermis, enabling potential applications as wearable skin-contact sensors. This work provides insight into the development of degradable and high sensing performance sensors suitable for applications in electronic skins and health monitoring devices.

A Soft Inductive Bimodal Sensor for Proprioception and Tactile Sensing of Soft Machines.

The somatosensory system is crucial for living beings to survive and thrive in complex environments and to interact with their surroundings. Similarly, rapidly developed soft robots need to be aware of their own posture and detect external stimuli. Bending and force sensing are key for soft machines to achieve embodied intelligence. Here, we present a soft inductive bimodal sensor (SIBS) that uses the strain modulation of magnetic permeability and the eddy-current effect for simultaneous bidirectional bending and force sensing with only two wires. The SIBS is made of a flexible planar coil, a porous ferrite film, and a soft conductive film. By measuring the inductance at two different frequencies, the bending angle and force can be obtained and decoupled. Rigorous experiments revealed that the SIBS can achieve high resolution (0.44° bending and 1.09 mN force), rapid response, excellent repeatability, and high durability. A soft crawling robot embedded with one SIBS can sense its own shape and interact with and respond to external stimuli. Moreover, the SIBS is demonstrated as a wearable human-machine interaction to control a crawling robot via wrist bending and touching. This highlights that the SIBS can be readily implemented in diverse applications for reliable bimodal sensing.

All-Textile Piezoelectric Nanogenerator Based on 3D Knitted Fabric Electrode for Wearable Applications.

Flexible, air permeable and elastic self-powered sensors for human motion monitoring and assisted medical rehabilitation have recently become a hot research topic. However, most current piezoelectric sensors can not account for many characteristics. Addressing this challenge, an all-textile piezoelectric sensor (ATPS) based on 3D structured knitted fabric electrodes is reported. The ATPS consists of a piezoelectric element polyvinylidene fluoride nanofiber membrane, flexible knitted fabric electrodes, and an elastic self-adhesive bandage. Based on the flexible and efficient knitting technology, the sensor has the advantages of low cost, flexibility, simple structure, and convenient large-area manufacturing. Experimental and finite element simulation results show that the knitting pattern of fabric electrodes can enhance the piezoelectric output of ATPS. The optimal ATPS has a high voltage response sensitivity of up to 0.68 V/kPa. The proposed ATPS responds to a wide range of input forces from 0.098 to 724 N in self-powered mode, verifying its feasibility as a tactile sensor for human motion detection and recognition (throat swallowing, wrist bending, elbow bending, knee bending, walking slowly, running fast) and as a pressure sensor (Morse code, digit recognition) and demonstrating its potential for motion tracking, medical rehabilitation, and human-computer interaction.

A highly-sensitive wearable capacitance pressure sensor based on calcium copper titanate/polydimethysiloxane/graphene oxide and polydimethysiloxane/silver nanowires sanwich strustures combination for human body monitoring

In recent years, flexible pressure sensors, with their high sensitivity, low detection limit, wide working pressure range and fast response speed, have been playing an important role in the development of wearable artificial devices, human-computer interaction and healthcare systems, and have attracted wide attention. However, the pressure sensors face challenges related to the weak tightness of bipolar materials, low charge density, and limitation in dielectric layers. In this paper, we present a novel configuration of flexible capacitive pressure sensors, utilizing a polydimethysiloxane (PDMS) thin film covered by silver nanowires (PDMS/SN, PSN) as the electrode materials and a porous material composed of calcium copper titanate (@CCTO), PDMS and graphene oxide (GO)(@CCTO/PDMS/GO, @CPG) as the positive electrode material. The sacrificial material, sugar, is employed to create dense internal pores within the substrate material, @CPG, leading to the formation of a profoundly porous substrate. The integration of the flexible capacitive pressure sensor using @CPG/PSN results in enhanced output performance. The modified sensors achieves a sensitivity of 0.22 kPa−1, which is 7 times higher than that of a pure PDMS dielectric layer sensor. Moreover, the sensors has a response time of 87 ms, a low detection pressure of 5 Pa with an extensive detection range from 0 to 150 kPa, and are capable of enduring 7200 cycles without sustaining damage. To validate the practical performance of the @CPG/PSN sensor, various human body activities are detected, including swallowing, coughing, neck bending, wrist bending, elbow bending, finger flexing, and holding objects like cups using a digitally designed glove capable of accommodating different materials. The pressure sensor based on @CPG/PSN demonstrates significant promise in detecting both low and high pressures, thus expanding the potential applications of capacitive pressure sensors.

Research on multiwalled carbon nanotubes spray method for preparing flexible piezoresistive tactile sensor

AbstractFlexible piezoresistive tactile sensor (FPTS) is widely used in wearable devices, e‐skin, and so on. However, the performance consistency and durability hinder its widespread application at a larger scale. It is still a challenge to prepare conductive composites with high performance consistency and high durability. In this research, a multiwalled carbon nanotubes (MWCNTs)/polydimethylsiloxane FPTS with high performance consistency and high durability was prepared by a combination of spray and spin coating method. The spray parameters of MWCNTs solution were optimized by numerical simulation, and a self‐developed high pressure spray device was adopted to realize the high‐pressure spray. In the 6000 tensile cycles experiments, the fluctuation of FPTS resistance is less than 5%. The range of prepared FPTS can reach 1.2 kPa, and the sensitivity is 0.8 kPa−1. The results of mouse click and wrist bending tests confirmed that the prepared FPTS can satisfy the detection requirements of wearable devices.

Lignin reinforced tough, adhesive and recoverable protein organohydrogels for wearable strain sensing under sub-zero temperatures

Protein-based hydrogels with promising biocompatibility and biodegradability have attracted considerable interest in areas of epidermal sensing, whereas, which are still difficult to synchronously possess high mechanical strength, self-adhesion, and recoverability. Hence, the bio-polymer lignosulfonate-reinforced gluten organohydrogels (GOHLx) are fabricated through green and simple food-making processes and the following solvent exchange with glycerol/water binary solution. Ascribing to the uniform distribution of lignosulfonate in gluten networks, as well as the noncovalent interactions (e.g., H-bond) between them, the resultant GOHLx exhibit favorable conductivity (~14.3 × 10−4 S m−1), toughness (~711.0 kJ m−3), self-adhesion (a maximal lap-shear strength of ~33.5 kPa), high sensitivity (GF up to ~3.04) and durability (~3000 cycles) toward shape deformation, which are suitable for the detection of both drastic (e.g., elbow and wrist bending) and subtle (e.g., swallowing and speaking) human movements even under −20 °C. Furthermore, the GOHLx is also biocompatible, degradable, and recoverable (by a simple kneading process). Thus, this work may pave a simple, green and cheap way to prepare all-biomass-based, tough, sticky, and recoverable protein-based organohydrogels for epidermal strain sensing even in harsh environments.

Self-healing and adhesive MXene-polypyrrole/silk fibroin/polyvinyl alcohol conductive hydrogels as wearable sensor

Conductive hydrogels become increasing attractive for flexible electronic devices and biosensors. However, challenges still remain in fabrication of flexible hydrogels with high electrical conductivity, self-healing capability and adhesion property. Herein, a conductive hydrogel (PSDM) was prepared by solution-gel method using MXene and dopamine modified polypyrrole as conductive enhanced materials, polyvinyl alcohol and silk fibroin as gel networks, and borax as cross-linking agent. Notably, the PSDM hydrogels not only showed high permeability (13.82 mg∙cm−2∙h−1), excellent stretch ability (1235 %), high electrical conductivity (11.3 S/m) and long-term stability, but also exhibited high adhesion performance and self-healing properties. PSDM hydrogels displayed outstanding sensing performance and durability for monitoring human activities including writing, finger bending and wrist bending. The PSDM hydrogel was made into wearable flexible electrodes and realized accurate, sensitive and reliable detection of human electromyographic and electrocardiographic signals. The sensor was also applied in human-computer interaction by collecting electromyography signals of different gestures for machine learning and gesture recognition. According to 480 groups of data collected, the recognition accuracy of gestures by the electrodes was close to 100 %, indicating that the PSDM hydrogel electrodes possessed excellent sensing performance for high precision data acquisition and human-computer interaction interface.

A High‐Stretchability, Wide Detection Range, and Wide Temperature Range Ti3C2Tx MXene/Graphene Strain Sensor Based on a Buckling Structure

AbstractFlexible wearable sensors have the characteristics of flexibility, comfort, and wearability, and have shown great potential in future electronic products. Despite significant efforts in developing stretchable electronic materials and structures, the development of flexible strain sensors with a wide temperature range, high sensitivity, broad detection range, and good interface stability remains challenging. Here, strain sensors with buckled structures are fabricated using high and low‐temperature resistant material Ti3C2Tx MXene/graphene, PDMS 184. The conductive material Ti3C2Tx MXene/graphene exhibits excellent interface interaction with PDMS 184, addressing not only the poor compatibility issue between the conductive material and the flexible substrate, but also demonstrating good stability and cycling performance. Buckled structure improves the stretchability and linearity of strain sensors. The fabricated strain sensor is suitable for a wide temperature range (−40 to 120 °C) and exhibits high stretchability (120% strain). The strain sensor demonstrates rapid response times at different temperatures: −40 (72.6 ms), 0 (62.7 ms), and 120 °C (52.7 ms). The strain sensor exhibits high sensitivity at different temperatures: −40 (GF = 0.38), 0 (GF = 0.24), 40 (GF = 0.66), and 120 °C (GF = 1.47). The strain sensor has a wide detection range (0.1% to 120%) and excellent cycling stability. In addition, Ti3C2Tx MXene/graphene strain sensors can accurately capture various human activities, such as blinking, speaking, finger bending, and wrist bending.

Unleashing the potential: Multifunctionality of PVDF-HFP based ternary nanocomposite films - magnetoelectric, energy harvesting and impact sensing performance

Multifunctional materials are proving to be highly promising for advancing various technologies, including magneto-mechano-electric energy harvesting devices and flexible sensors. This study focused on synthesizing a polyvinylidene fluoride-hexafluoropropylene-metal-oxide-layered silicate nanocomposite system using a cost-effective solution casting technique. The performance of the system was evaluated in terms of magnetoelectric behaviour, energy harvesting capabilities, and impact sensing. The nanocomposite films demonstrated a peak-to-peak voltage of 12.2 V with a filler loading of 15 wt% and an applied force of 9 N, along with a magnetoelectric coupling coefficient of 20.6 mVcm−1Oe−1. The device's ability to scavenge biomechanical energy during body movements like foot stamping, arm bending, finger flexing, and wrist bending was successfully verified. Furthermore, rigorous durability testing was conducted through repeated energy harvesting studies, proving the device's practicality and resilience. Notably, the developed device powered up six LEDs and a digital clock, while the impact sensor exhibited a linear relationship between output voltage and impact force. These findings highlight the remarkable potential of the polyvinylidene fluoride-hexafluoropropylene-metal-oxide-layered silicate nanocomposite system for multifunctional applications in various technological fields.

Synthesis of Superelastic, Highly Conductive Graphene Aerogel/Liquid Metal Foam and its Piezoresistive Application.

Graphene aerogel (GA) has important application potential as piezoresistive sensors due to its low density, high conductivity, high porosity, and good mechanical properties. However, the fabrication of GA-based sensors with good mechanical properties and excellent sensing performance is still challenging. Herein, liquid- metal-modified GAs (GA/LM) are proposed for the development of an excellent GA-based sensor. GA/LM with three-dimensional interconnected layered structure exhibits excellent compressive stress of 41 KPa and fast response time (<20 ms). While generally flexible GA composites cannot be compressed beyond 80 % strain without plastic deformation, GA/LM demonstrates a high compressive strength of 60 kPa under a strain of 90 %. A real-time pressure sensor was fabricated based on GA/LM-2 to monitor swallowing, pulse beating, finger, wrist and knee bending, and even plantar pressure during walking. These excellent features enable potential applications in health detection.

A skin-wearable and self-powered laminated pressure sensor based on triboelectric nanogenerator for monitoring human motion

Flexible and skin-wearable triboelectric nanogenerators (TENGs) have emerged as promising candidates for self-powered tactile and pressure sensors and mechanical energy harvesters due to their compatible design and ability to operate at low frequencies. Most research has focused on improving tribo-negative materials for flexible TENGs, given the limited options for tribo-positive materials. Achieving biocompatibility while maintaining the sensitivity and capability of energy harvesting is another critical issue for wearable sensors. Here, we report a TENG-based biocompatible and self-powered pressure sensor by simple fabrication of layer-by-layer deposition methods. The Laminated Flexible-TENG comprises polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) films embedded within a flexible and biocompatible polydimethylsiloxane (PDMS) matrix. A nanostructured PDMS surface obtained by oxygen plasma facilitated the sputter deposition of a layered indium tin oxide copper electrode and a tribo-positive PMMA thin layer on top. The addition of the indium tin oxide layer to copper significantly improved the quality and performance of the indium tin oxide-copper electrode. Self-powered Laminated Flexible-TENGs demonstrated impressive pressure-sensing capabilities, featuring dual sensitivity of 7.287 V/kPa for low pressure and 0.663 V/kPa for higher pressure. Moreover, the PDMS-encapsulated TENG sensor effectively traced the physiological motions, such as wrist and finger bending, and efficiently harnessed the waste energy from everyday physical activities, such as walking and jogging. The maximum peak-to-peak voltages of 18.3 and 57.4 V were recorded during these motions. Encapsulated TENGs have broad potential in wearable technology, including healthcare, human-machine interfaces, and energizing microelectronics.