Wearable Sensor Applications Research Articles

Anti-freezing conductive zwitterionic composite hydrogels for stable multifunctional sensors

Zwitterionic conductive hydrogels have shown potential application in wearable strain and pressure sensors. However, there are still fundamental challenges to achieve zwitterionic hydrogels with excellent mechanical properties, able to keep flexibility at sub-zero temperatures. To overcome these limitations, a zwitterionic conductive hydrogel was fabricated in this work by in-situ polymerization of aniline (ANI) monomer in a copolymer of sulfobetaine methacrylate (SBMA) and acrylic acid (AA) matrix. The obtained hydrogel possesses outstanding anti-freezing performance (without obvious loss of stretchability at −18 °C) and water-retaining properties, due to the introduction of LiCl on the zwitterionic polymer matrix. The synergy of chemical and physical crosslinking between poly (SBMA-co-AA) and polyaniline (PANI) networks enhance the mechanical performance of the zwitterionic hydrogel, that exhibits a fracture tensile strength of 470 kPa, and a fracture strain up to 600 %. Additionally, the integration of PANI confers stable conductivity (2.23 S m−1, maintained at 1.89 S m−1 even at −18 °C), high sensitivity (GF = 1.74), and short response and recovery times (223 ms and 191 ms, respectively). The hydrogel can be applied as a flexible sensor to accurately detect various human motions. This work provides a feasible strategy for developing wearable multifunctional sensors in a wide working temperature range.

Biomass aerogel composite containing BaTiO3 nanoparticles and MXene for highly sensitive self-powered sensor and photothermal antibacterial applications

Biomass aerogel materials are increasingly attracting researchers’ attention because of good biocompatibility of biomass materials and multiple functional features of aerogel materials. Herein, novel biomass aerogel composite was fabricated by doping hydroxylated barium titanate (BT-OH) nanoparticles and MXene in chitosan/bacterial cellulose (CB) aerogel by simple methods containing chemical modification, physical mixture and lyophilization. The novel aerogel composite named CB/BT-OH/MXene showed favorable piezoelectric properties and excellent photothermal antibacterial properties. The aerogel composite-based piezoelectric sensor displayed short response time (0.4 s), high response sensitivity (800 mV/N), and long cycle stability (over 1000 cycles), which could monitor various body movements, including fingers bending, speaking, wrist bending, elbow bending, smiling, and walking. Moreover, the aerogel composite possessed satisfactory photothermal conversion ability, which could reach 55 ℃ by 10 s of near-infrared irradiation (808 nm, 0.2 W/cm2), successfully achieving complete sterilization effect towards S. aureus and E. coli. The novel biomass aerogel composite may find its potential applications in wearable or implantable self-powered sensors with satisfactory antibacterial performance.

Mechanically Tough and Highly Stretchable Hydrogels Based on Polyurethane for Sensitive Strain Sensor.

Hydrogels with flexible and stretchable properties are ideal for applications in wearable sensors. However, traditional hydrogel-based sensors suffer from high brittleness and low electrical sensitivity. In this case, to solve this dilemma, a macromolecular polyurethane crosslinking agent (PCA) was designed and prepared; after that, PCA and two-dimensional (2D) MXene nanosheets were both introduced into a covalently crosslinked network to enhance the comprehensive mechanical and electrochemical properties of the hydrogels. The macromolecular polyurethane crosslinking agent promotes high-tensile strength and highly stretchable capacity by suitable covalent crosslinking. The optimized hydrogel, which exhibited maximum tensile strength and maximum elongation at break, had results of 1.21 MPa and 644%, respectively. Two-dimensional MXene nanosheets provide hydrogel with high electrical conductivity and strain sensitivity, producing a wearable device for the continuous monitoring of human movements and facial microexpressions. This study demonstrated an efficient structure design strategy for building mechanically tough, highly stretchable, and sensitive dual-mode MXenes-based wearable sensors.

Fabrication of amphoteric gelatin nanospheres-doped self-healing nanocomposite hydrogels and the application in flexible sensors

The nanomaterials with two distinct properties or components have outstanding advantages in the synthesis of smart hydrogels. In this work, gelatin nanospheres (GNPs) asymmetrically coated with poly(diallyldimethylammonium chloride) (PDDA) and tannic acid (TA) were synthesized by Pickering emulsion template method. The nanocomposite hydrogel with amphoteric gelatin nanospheres (GPTNPs)-doped was successfully prepared, which has excellent mechanical properties (strain = 616%, stress = 2.85 MPa) and self-healing properties (efficiency = 90.9%) under the synergistic effects of hydrogen bonding and metal coordination. The developed GPTNPs/polyacrylic acid (GPTNPs/PAA) hydrogel sensor exhibits high sensitivity (gauge factor (GF) = 3.69), quick response time (96.4 ms) and superior stability. Therefore, the GPTNPs/PAA hydrogels are excellent materials for application in wearable flexible sensors to monitor real-time human motion.

Tough, recyclable and biocompatible carrageenan-modified polyvinyl alcohol ionic hydrogel with physical cross-linked for multimodal sensing

Biocompatibility hydrogel conductors are considered as sustainable bio-electronic materials for the application of wearable sensors and implantable devices. However, they mostly face the limitations of mismatched mechanical properties with skin tissue and the difficulty of recycling. In this regard, here, a biocompatible, tough, reusable sensor based on physical crosslinked polyvinyl alcohol (PVA) ionic hydrogel modified with ι-carrageenan (ι-CG) helical network was reported. Through simulating the ion transport and network structure of biological systems, the ionic hydrogels with skin-like mechanical features exhibit large tensile strain of 640 %, robust fracture strength of 800 kPa, soft modulus and high fatigue resistance. Meanwhile, the ionic hydrogel-based sensors possess a high response to strain/pressure over a wide range and could be utilized for multimodal sensing of human activity signals. Benefit from biosafety and temperature reversibility of ι-CG and PVA endow hydrogels with not only biocompatibility, but also meaningfully recyclability. The as-prepared hydrogels could be freely reconstructed into new flexible electronics and safely integrated with the human skin. It could be anticipated that the physically cross-linked ionic hydrogel conductor could expand the options for next-generation bio-based sensors.

Self-Powered Integrated System with a Flexible Strain Sensor and a Zinc-Air Battery.

At present, self-powered, lightweight, and flexible sensors are widely applied, especially in the fields of wearable devices and human health monitoring. Nevertheless, conventional self-powered flexible sensor systems rely on power supply components such as supercapacitors, nanofriction generators, and solar cells, which present certain limitations, such as high dependence on external environmental factors and the inability to provide long-term stable energy supply. Thus, a paramount exigency emerges for the development of wearable sensors endowed with enduring battery life to enable continuous monitoring of human motion for extended periods. In our academic study, we present an innovative self-powered sensing system that seamlessly combines a pliable zinc-air battery with a strain sensor. This approach offers a stable output signal over extended periods without an external energy device, which is crucial for long-term, continuous human motion monitoring. Through the incorporation of various carbon materials, we realized the multifunction of poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) dual network hydrogels and prepared zinc-air battery electrolytes and strain sensors. Notably, the batteries exhibit impressive power density (82.5 mW cm-2), high open-circuit voltage (1.42 V), and remarkable environmental stability. Even when subjected to puncture and breakage, the batteries remain operational without suffering from electrolyte leakage. Similarly, our strain sensor boasts a broad working range spanning from 0 to 1400%, coupled with a remarkable sensitivity (GF = 2.99) and exceptional capacity to accurately detect various mechanical deformations. When integrated into a single system, the integrated system can monitor human movement for up to 10 h, which has broad prospects in wearable sensor applications.

Tannic acid-coated cellulose nanocrystal-reinforced transparent multifunctional hydrogels with UV-filtering for wearable flexible sensors

Ionically conductive hydrogels are an ideal alternative material for applications in wearable flexible sensors to monitor human health. However, producing hydrogels with both high sensitivity and excellent versatility is difficult, and their transparency and UV-blocking properties are significantly limited. Here, with mussel- and gecko-inspired biomimicry, all-biomass-based hydrogels (OGTCGs) with self-adhesive, self-healing, transparent, UV-filtering, frost-resistant, environmentally stable, antibacterial, and biocompatible properties were designed and constructed via a simple one-step approach with a water/glycerol system and borax added without any crosslinker using synergistic dynamic covalent and noncovalent chemistry. The transparency of the OGTCG hydrogel reached 81.06 %, while the added tannic acid-coated cellulose nanocrystal (TA@CNC) induced a UV-blocking effect. The OGTCG hydrogel exhibited a high toughness (218.67 kPa) and modulus (100.32 kPa) reinforced by TA@CNC. The OGTCG hydrogel showed good self-healing abilities with an efficiency of over 90 % after 6 h. In a binary solvent system, the OGTCG hydrogel had environmental stability, as illustrated by density functional theory (DFT), greatly broadening its application range. Moreover, it had an electrical conductivity of 2.3 mS cm−1 and a sensitivity of 3.97. Therefore, with its rapid response and real-time monitoring capabilities, the OGTCG hydrogel shows great potential for applications in monitoring human health.

Fully degradable chitosan–based triboelectric nanogenerators applying in disposable medical products for information transfer

Chitosan (CS) is a natural material with remarkable biocompatibility, biodegradability, and electron-donating ability, making it an excellent candidate for use in triboelectric nanogenerators (TENGs) for the development of wearable sensors. The output performance of CS has been improved by modifications with fillers or functional groups. However, it is still difficult to realize excellent power generation and desired degradation simultaneously. Herein, we design a CS friction layer by plasticizer addition and a template method to obtain a high–performance and fully degradable TENG–based sensor for effective information transmission. Because of the microstructure design of the friction film and glycerol plasticizer addition, the CS–glycerol friction layer has a high contact area in the friction process. Therefore, this CS–glycerol TENG achieves a higher output performance with an open–circuit voltage of 127 V, 2.32 times higher than that of a CS–based TENG fabricated without a template method. Finally, the CS–glycerol TENG sensor is used in an alphabetic code transfer application and can be completely degraded in the soil within 69 days after completing its working cycle. The template and plasticizer strategy effectively improves the CS based TENG output performance and maintains the complete degradation. Furthermore, because of the extensibility, positive cooling ability, and antibacterial activity, the degradable CS–glycerol TENG sensor has great potential for application in multifunctional wearable sensors, especially for disposable medical products.

A polyester/spandex blend fabrics-based e-textile for strain sensor, joule heater and energy storage applications

Electronic textiles (e-textiles), as a new class of wearable electronics, have shown diverse applications in modern technologies. However, the development of multi-functional e-textiles with both high strength and elasticity to satisfy different working conditions remains challenge. Herein, the e-textiles based on polyester/spandex blend (PSB) fabrics have been fabricated and their applications in strain sensors, heaters and supercapacitors have been systematically studied. The carbon nanotubes (CNTs) are coated on PSB fabrics via polydopamine (PDA) adhesion. As a strain sensor, the air-permeable PSB-CNT e-textiles show a gauge factor of 18.9 at high strain with a fast response time of 114 ms. The PSB-CNT strain sensor can work better than the cotton-based sensor even at high temperature of 100 °C due to the high heat resistance of polyester, securing its application in severe environment. As a joule heater, the PSB-CNT e-textiles can raise up to 110 °C at 12 V. Further electrodeposition of polypyrrole (PPy) on PSB-CNT can obtain the e-textile electrodes for micro-supercapacitor (MSC). The all-solid-state MSC using PSB-CNT-PPy delivers high specific capacitance of 550 mF cm−2 at 1 mA cm−2. This work offers a simple route for e-textile fabrications and promises potential applications in wearable sensors, heaters, and power sources.

(Invited) towards Continuous Health Monitoring Platforms By Enzyme-Free Electrochemical Sensors and Triboelectric Sensors for Noninvasive Lactate Detection

Emerging wearable devices with non-invasively biosensing technics have drawn considerable attention to continuously monitor several metabolites in body fluids, such as a tear, saliva, and sweat, to diagnose human health conditions. Most importantly, wearable sensors could offer unique possibilities for online, real-time and non-invasive monitoring of health compared to traditional invasive biosensors. Among lots of analytes, lactic acid concentration in the human body exhibits a high relationship with several diseases such as acute heart diseases, hypoxia, muscle fatigue, meningitis, and cystic fibrosis, and it could also cause muscle pain in athletes. To further boost up the reproducibility and reliability of wearable biosensors to detect lactate concentration levels from human sweat, Ni-based layered double hydroxide (LDH) with various secondary transition metals (Fe and Co) was proposed as electrocatalysts in an enzyme-free electrochemical lactate sensor. According to the mechanism of lactate oxidation on the transition metal-based electrocatalyst, secondary transition metal of Co could serve as the active site for lactate oxidation and facilitate the adsorption of OH- in the alkaline electrolyte. To further increasing the active surface area for enhancing the sensitivity of Ni-based LDH, ZIF-67 derived NiCo LDH was synthesized as the electrocatalyst for non-enzymatic lactate detection. Co-based ZIF-67 served as self-sacrificial templates to fabricate hierarchically structural NiCo LDH with uniform porosity and high electrochemically active surface area to achieve outstanding electrocatalytic performance for lactate sensing. After optimizing the particle size of ZIF-67 and transformation times, ZIF-67 derived NiCo LDH reached the ultrahigh sensitivity of 83.98 μA mM- 1 cm- 2 at an applied potential of 0.55 V (vs. Ag/AgCl KCl sat’d) in the concentration range from 2 to 26 mM. On the other hand, pioneering works in biosensors for lactate detection in sweat has been encountered major challenges such as noble material usage, immobile power supply, and complicated circuit connection to realize the compact sustainable sensing systems. To solve these restrictions, herein, the self-powered molecular imprinted polymers based triboelectric sensor (MIP-TES) was designed to offer a multifunctional noninvasive approach for specific and simultaneous lactate detection. Free-standing PVDF/graphene flexible electrode modified poly(3-aminophenyl boronic acid) imprinted lactate molecule demonstrated the change of the surface properties afterlactate adsorption. MIP-modified electrode revealed the selective lactate sensing over non molecular imprinted polymers (NIP) electrode through the superior and stable signal change with variation of lactate concentration in human sweat. Moreover, MIP modified lactate sensor was further introduced in the triboelectric nanogenerator system to harvest mechanical energy from contact and separation into electrical output. The more adsorbed lactate led to lower energy barriers and decreasing electrical potential when detecting higher lactate concentration. Self-power triboelectric lactate sensor could directly power the number of LED lights without an external energy supply. Eventually, it was validated the feasible application of wearable sensors on human skin. After introducing noninvasive enzyme-free biosensors and triboelectric sensors, an innovatively continuous non-invasive health monitoring platforms can be achieved for practical applications, especially in the areas of home medical examination and wearable personal biosensors.

3D printing a tear-resistant conductive organogel used for wearable sensor

In recent years, ion conductive hydrogels based on photocurable 3D printing technology have attracted wide attention in the application of wearable sensors, which greatly simplifies the manufacturing process of devices, while making devices with high sensitivity and high fidelity. However, the current ionic hydrogel network via photocuring 3D printing is mainly crosslinked by covalent bonds. Due to the lack of sufficient energy dissipation and high-functionality cross-links within the network, the gel will inevitably crack after continuous dynamic loading. Here, we designed an organic gel with excellent tear resistance, which is mainly attributed to the high-functionality cross-links constructed by nano-clay containing a large number of hydroxyl groups. Specifically, the precursor of the organic gel is mainly composed of N-methylol acrylamide (NAM), nano-clays, photoinitiator, and water-glycerol binary solvent system. After photocurable printing, lots of hydrogen bonds are formed between nano-clays and poly-NAM network, which not only provides an energy dissipation mechanism for the gel network, but also acts as a nanoscale cross-linking site to resist crack propagation during the stretching of the gel. Under the action of nano-clay, the tear resistance of the gel has been greatly improved. In addition, the sodium ions released by the nano-clay ensure the good ionic conductivity of the gel, verifying its potential as a strain sensor with high sensitivity. What's more, combining skin-like organic gels and 3D printing technology enables the manufacture of highly sensitive sensors much easier and more designable. This study not only provides a method for the preparation of high-precision ionic conductors with excellent tear resistance, but also clears the way for developing a new class of wearable devices and intelligent electronics.

Implementing Wearable Sensors for Clinical Application at a Surgical Ward: Points to Consider before Starting.

Incorporating technology into healthcare processes is necessary to ensure the availability of high-quality care in the future. Wearable sensors are an example of such technology that could decrease workload, enable early detection of patient deterioration, and support clinical decision making by healthcare professionals. These sensors unlock continuous monitoring of vital signs, such as heart rate, respiration rate, blood oxygen saturation, temperature, and physical activity. However, broad and successful application of wearable sensors on the surgical ward is currently lacking. This may be related to the complexity, especially when it comes to replacing manual measurements by healthcare professionals. This report provides practical guidance to support peers before starting with the clinical application of wearable sensors in the surgical ward. For this purpose, the Non-Adoption, Abandonment, Scale-up, Spread, and Sustainability (NASSS) framework of technology adoption and innovations in healthcare organizations is used, combining existing literature and our own experience in this field over the past years. Specifically, the relevant topics are discussed per domain, and key lessons are subsequently summarized.

Electrospinning Evolution Derived from TRIZ Theory for Directly Writing Patterned Nanofibers.

Nanofibers (NFs) have the advantages of tremendous flexibility, small size and a high surface-to-weight ratio and are widely used in sensors, drug carriers and filters. Patterned NFs have expanded their application fields in tissue engineering and electronics. Electrospinning (ES) is widely used to prepare nonwoven NFs by stretching polymer solution jets with electric forces. However, patterned NFs cannot be easily fabricated using ordinary ES methods: the process gradually deteriorates them as repulsion effects between the deposited NFs and the incoming ones increase while residual charges in the fibers accumulate. Repulsion effects are unavoidable because charges in the polymer solution jets are the fundamental forces that are meant to stretch the jets into NFs. TRIZ theory is an effective innovation method for resolving conflicts and eliminating contradictions. Based on the material-field model and the contradiction matrix of TRIZ theory, we propose a strategy to improve ES devices, neutralizing the charges retained in NFs by alternating the current power of the correct frequency, thus successfully fabricating patterned NFs with clear boundaries and good continuity. This study demonstrates a strategy for resolving conflicts in innovation processes based on TRIZ theory and fabricating patterned NFs for potential applications in flexible electronics and wearable sensors.

Ultrafast volumetric assembly of layered nanocomposites at dynamic gelation interface

Biomimetic learning has boosted the development of layered nanocomposites with superior mechanical properties, fast ion conduction, high barrier capacities, and high conductivities, resulting in numerous practical applications in artificial structural materials, energy storage, filtration, and electromagnetic shielding. These outstanding properties arise from the highly oriented layered structure. Convenient fabrication and complex shapes are required for practical applications. However, conventional strategies, including ice templating, vacuum filtration, and electromagnetic induction, are constrained by time-consuming fabrication and sample shapes, restricting their extension to large-scale applications. Here, we present a facile, universal, and scalable strategy for fabricating layered nanocomposites using ion diffusion-induced directional gelation. This ultrafast volumetric production, including controllable thickness growth with no size restriction, results from continuous gelation and convenient post-processing, whose fabrication rate is 21.7 times that of ice templating, 13.2 times that of vacuum filtration, and 3.1 times that of electromagnetic induction. Furthermore, layered alumina/epoxy nanocomposites were prepared with superior specific strength (2.9 MPa m1/2/(Kg/m3)) and specific toughness (96.2 MPa/(Kg/m3)), demonstrating the validity of our strategy for layered structures. Moreover, our approach can be extended to other material systems and arbitrary shapes for multifunctional applications in wearable devices, sensors, and anti-corrosion coatings.

High-Performing Conductive Hydrogels for Wearable Applications.

Conductive hydrogels have gained significant attention for their extensive applications in healthcare monitoring, wearable sensors, electronic devices, soft robotics, energy storage, and human-machine interfaces. To address the limitations of conductive hydrogels, researchers are focused on enhancing properties such as sensitivity, mechanical strength, electrical performance at low temperatures, stability, antibacterial properties, and conductivity. Composite materials, including nanoparticles, nanowires, polymers, and ionic liquids, are incorporated to improve the conductivity and mechanical strength. Biocompatibility and biosafety are emphasized for safe integration with biological tissues. Conductive hydrogels exhibit unique properties such as stretchability, self-healing, wet adhesion, anti-freezing, transparency, UV-shielding, and adjustable mechanical properties, making them suitable for specific applications. Researchers aim to develop multifunctional hydrogels with antibacterial characteristics, self-healing capabilities, transparency, UV-shielding, gas-sensing, and strain-sensitivity.

Strong, Tough, and Anti-Swelling Supramolecular Conductive Hydrogels for Amphibious Motion Sensors.

Conductive polymer hydrogels (CPHs) are widely employed in emerging flexible electronic devices because they possess both the electrical conductivity of conductors and the mechanical properties of hydrogels. However, the poor compatibility between conductive polymers and the hydrogel matrix, as well as the swelling behavior in humid environments, greatly compromises the mechanical and electrical properties of CPHs, limiting their applications in wearable electronic devices. Herein, a supramolecular strategy to develop a strong and tough CPH with excellent anti-swelling properties by incorporating hydrogen, coordination bonds, and cation-π interactions between a rigid conducting polymer and a soft hydrogel matrix is reported. Benefiting from the effective interactions between the polymer networks, the obtained supramolecular hydrogel has homogeneous structural integrity, exhibiting remarkable tensile strength (1.63MPa), superior elongation at break (453%), and remarkable toughness (5.5MJ m-3 ). As a strain sensor, the hydrogel possesses high electrical conductivity (2.16S m-1 ), a wide strain linear detection range (0-400%), and excellent sensitivity (gauge factor = 4.1), sufficient to monitor human activities with different strain windows. Furthermore, this hydrogel with high swelling resistance has been successfully applied to underwater sensors for monitoring frog swimming and underwater communication. These results reveal new possibilities for amphibious applications of wearable sensors.

Ultrastretchable, repairable and highly sensitive xanthan collagen nanosilver hydrogel for wide temperature flexible sensing

Conductive hydrogels, lauded for their electrical conductivity, precise information capture, biocompatibility, and extensibility, have gained prominence as ideal candidate materials for flexible wearable sensor applications. Nevertheless, these sensors must surmount numerous challenges such as environmental temperature variations, bacterial growth in high-humidity environments, low signal detection sensitivity, irreversible damage, and mechanical performance stability during use. In response to these challenges, we present a hydrophobic supramolecular and dynamic coordination double-network hydrogel, prepared through a solvent-exchange method, with an accelerated gelation rate. The coordination of dynamic hydrogen bonds and coordination bonds within the hydrophobic supramolecular network imbues the hydrogel with superior mechanical properties (elongation at break around 4900%, tensile strength approximately 506 kPa) and improved self-healing capabilities. This solvent-exchange-mediated hydrogel exhibits broad temperature resilience (−20–60 °C) and reliable repeatability. Additionally, the sensor enables wireless human signal monitoring with a rapid response time (75 ms) and heightened sensitivity (gauge factor = 22.34). The wearable sensor’s antibacterial efficacy effectively suppresses bacterial propagation in high-moisture hydrogels, with a bacterial inhibition rate of 99.9%. The findings from our series of studies reveal the successful fabrication of stable, flexible wearable sensors with self-healing, antibacterial, high sensitivity, and broad temperature tolerance characteristics, showcasing the immense potential for applications in wearable electronics, wireless monitoring, and human–machine interactions.

A stretchable, biocompatible, and self-powered hydrogel multichannel wireless sensor system based on piezoelectric barium titanate nanoparticles for health monitoring

Piezoelectric hydrogel-based sensors have emerged as a promising technology for accurately monitoring various physiological signals of the human body without the need for an external power source. The multichannel wireless sensing systems with high data acquisition efficiency and low maintenance cost markedly broaden the application of wearable sensors. However, the challenges that these sensors face is that the low voltage output can cause the output signal to be easily covered by noise when used in a multi-signal acquisition system. Here, a stretchable, biocompatible, piezoelectric hydrogel sensor is fabricated and integrated with self-developed signal processing/transmission modules to obtain a multichannel wireless sensing system. Furthermore, the system can stably and real-time wirelessly monitor physiological signals of the human body. Overall, this work represents a significant advancement in the field of piezoelectric hydrogel-based wireless multichannel sensing systems and has the potential to be applied in a wide range of complex scenarios.

Thermally Drawn Multi-material Fibers Based on Polymer Nanocomposite for Continuous Temperature Sensing

With increasing personalized healthcare, fiber-based wearable temperature sensors that can be incorporated into textiles have attracted more attention in the field of wearable electronics. Here, we present a flexible, well-passivated, polymer–nanocomposite–based fiber temperature sensor fabricated by a thermal drawing process of multiple materials. We engineered a preform to optimize material processability and sensor performance by considering the rheological and functional properties of the preform materials. The fiber temperature sensor consisted of a temperature-sensing core made from a conductive polymer composite of thermoplastic polylactic acid, a conductive carbon filler, reduced graphene oxide, and a highly flexible linear low-density polyethylene passivation layer. Our fiber temperature sensor exhibited adequate sensitivity (− 0.285%/°C) within a temperature range of 25–45 °C with rapid response and recovery times of 11.6 and 14.8 s, respectively. In addition, it demonstrated a consistent and reliable temperature response under repeated mechanical and chemical stresses, which satisfied the requirements for the long-term application of wearable fiber sensors. Furthermore, the fiber temperature sensor sewn onto a daily cloth and hand glove exhibited a highly stable performance in response to body temperature changes and temperature detection by touch. These results indicate the great potential of this sensor for applications in wearable, electronic skin, and other biomedical devices.Graphical

Emerging Functional Polymer Composites for Tactile Sensing.

In recent years, extensive research has been conducted on the development of high-performance flexible tactile sensors, pursuing the next generation of highly intelligent electronics with diverse potential applications in self-powered wearable sensors, human-machine interactions, electronic skin, and soft robotics. Among the most promising materials that have emerged in this context are functional polymer composites (FPCs), which exhibit exceptional mechanical and electrical properties, enabling them to be excellent candidates for tactile sensors. Herein, this review provides a comprehensive overview of recent advances in FPCs-based tactile sensors, including the fundamental principle, the necessary property parameter, the unique device structure, and the fabrication process of different types of tactile sensors. Examples of FPCs are elaborated with a focus on miniaturization, self-healing, self-cleaning, integration, biodegradation, and neural control. Furthermore, the applications of FPC-based tactile sensors in tactile perception, human-machine interaction, and healthcare are further described. Finally, the existing limitations and technical challenges for FPCs-based tactile sensors are briefly discussed, offering potential avenues for the development of electronic products.