Flexible Wearable Sensors Research Articles

Research Progress of Flexible Wearable Sensors Based on Protein Hydrogels

Natural protein-based hydrogels, which combine the biocompatibility, biodegradability, non-toxicity and adhesion of natural proteins, have been widely researched in the field of flexible and wearable sensors. In addition, the sensing capability of protein hydrogels can be elevated by improving their mechanical properties, electrical conductivity, self-healing adhesion and environmental stability. This paper reviews the research of protein-based hydrogels represented by silk fibroin, gelatin and keratin in flexible wearable sensors. Firstly, the preparation mechanism of these three proteins was introduced. Subsequently, we summarized the performance optimization strategies of protein-based hydrogels. Then, the application of protein-based hydrogels in flexible and wearable sensors is discussed. Finally, we summarized and prospected the recent research, which provided reference for the future relevant researchers.

All fabric and flexible wearable sensors for simultaneous sweat metabolite detection and high-efficiency collection

Wearable sweat electrochemical sensors have attracted wide attention due to their advantages of non-invasive, portable, real-time monitoring, etc. However, existing sensors still have some problems with efficient sweat collection. Microfluidic channel technology and electrospinning technology are commonly used to collect sweat efficiently, but there are some limitations such as complex channel design and multiple spinning parameters. Besides, existing sensors are mostly based on flexible polymers, such as, PET, PDMS, PI and PI, which have limited wearability and permeability. Based on the above, all fabric and dual-function flexible wearable sweat electrochemical sensor is proposed in this paper. This sensor uses fabric as the raw material to implement the directional transport of sweat and the multi-component integrated detection dual functions. Meanwhile, the high-efficiency collection of sweat is obtained by a Janus fabric, wherein one side of the selected silk is superhydrophobic graft treated and the other side is hydrophilic plasma treated. Therefore, the resulting Janus fabric can effectively transfer sweat from the skin side to the electrode, and the minimum sweat droplet can reach 0.2 μL to achieve micro-volume collection. Besides, the patterned sensor, made of silk-based carbon cloth, is fabricated using a simple laser engraving, which could detect Na+, pH, and glucose instantaneously. As a result, these proposed sensors can achieve good sensing performance and high-efficiency sweat collection dual functionality; moreover, it has good flexibility and comfortable wearability.

Silk-based conductive materials for smart biointerfaces.

Silk-based conductive materials are widely used in biointerface applications, such as artificial epidermal sensors, soft and implantable bioelectronics, and tissue/cell scaffolds. Such biointerface materials require coordinated physicochemical, biological, and mechanical properties to meet current practical needs and future sophisticated demands. However, it remains a challenge to formulate silk-based advanced materials with high electrical conductivity, good biocompatibility, mechanical robustness, and in some cases, tissue adhesion ability without compromising other physicochemical properties. In this review, we highlight recent progress in the development of functional conductive silk-based advanced materials with different morphologies. Then, we reviewed the advanced paradigms of these silk materials applied as wearable flexible sensors, implantable electronics, and tissue/cell engineering with perspectives on the application challenges. Silk-based conductive materials can serve as promising building blocks for biomedical devices in personalized healthcare and other fields of bioengineering.

MoS2‐Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

AbstractWearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS2‐polyaniline (PANI) modified screen‐printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS2 nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as‐fabricated biosensor exhibits high super‐Nernstian sensitivity of −70.4 ± 1.7 mV pH−1 in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na+, Cl−, K+, and NH4+ with tremendous long‐term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS2 and PANI are correlated with the boosted performance of the as‐produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real‐time noninvasive, skin attachable, and flexible wearable pH sensor.

Recent advances of flexible MXene physical sensor to wearable electronics

MXenes, as a family of two-dimensional (2D) lamellar material of transition metal carbides, nitrides and carbon/nitrides, is an ideal choice for flexible sensing materials because of its metal-like electrical conductivity, adjustable layer spacing, good hydrophilicity and mechanical properties. Flexible wearable sensors based on various electromechanical properties and structural forms of MXene have also emerged in recent years, such as MXene fiber-based fabrics, flexible membrane structures, and three-dimensional aerogel/hydrogel gel structures. All these structural sensors have shown different advantages and sensing effects, and some corresponding issues are also brought out. Therefore, the improvement of comprehensive performance for MXene based flexible sensors have always been a concern. In this review, the structure, fundamental properties, synthetic routes of MXene are briefly summarized. Additionally, the fabrication of flexible sensing materials with different configuration, and state-of-the-art progress of MXene based wearable physical sensors (including pressure, strain, humidity and temperature sensor) are highlighted. At last, the current challenges and their future research directions toward advancing wearable MXene sensors are presented and discussed.

Zinc-ion engineered Plant-based multifunctional hydrogels for flexible wearable strain Sensors, Bio-electrodes and Zinc-ion hybrid capacitors

Multifunctional hydrogels, particularly with superior mechanical properties and using green/sustainable approaches, have attracted increasing attention because of their many applications and consistency with the green chemistry principle; unfortunately, their effective fabrication process is challenging. In this work, inspired by unique functions in plant-derived components, a multifunctional polyacrylic acid (PAA) hydrogel was innovatively developed using ZnCl2 and biomass-derived materials. Ingeniously, ZnCl2 has multiple functions, in combination with cellulose, lignin, and citric acid (CA), delivering intriguing properties to the hydrogel system. As a solvent system, the ZnCl2 solution has extraordinary H-bonding-donating ability, dissolving cellulose macromolecular chains; subsequently, solubilized cellulose as green reinforced-fillers are added to hydrogel, improving the strength properties, with compression strength of ∼ 4.1 MPa, tensile strength of ∼ 795.4 kPa, and elongation at break of ∼ 620 %. The lignin-ZnCl2 catalysis system imparts a fast PAA gelation process, and the resultant hydrogel has strong/long-lasting/repeatable adhesive strength of 25.5 kPa (on Zn-carbon cloth) in 28 days. Additionally, ZnCl2 can form reversible ionic/electrostatic interactions with both lignin and CA, further improving the adhesive and mechanical properties. As anti-freezing agents, water-retaining agents and conducting medium, ZnCl2 also endows the hydrogel with desirable environmental compatibility and good conductivity (14.2 mS·cm−1). Furthermore, the presence of plant-based components endows the hydrogel with ultraviolet (UV) blocking, biocompatibility and antibacterial attribute. Significantly, the as-prepared hydrogels are suited for such diverse applications as flexible wearable strain sensors, bio-electrodes and zinc-ion hybrid capacitors (ZHCs), even can efficiently work at −65 °C. This study provides a new strategy of engineering multifunctional hydrogels using plant-based functional components, and these hydrogels show promising applications in many emerging areas including electronic skin sensors, health monitoring and energy storage devices.

A biodegradable wearable flexible sensor based on natural wheat flour polymer for human motion and sweat monitoring

Fabrication of economical and eco-friendly flexible sensors is highly demanded in developing wearable biomedical devices. In this study, an eco-friendly strain and sweat sensor has been successfully assembled based on innovative composites consisting of carbon black (CB) and natural flour polymer, which are entirely green and biodegradable. A film-based sensing device has been developed to measure electrical resistance and strain simultaneously and continuously, owing to the highly sensitive resistance responsibility of the as-developed hybrid of CB and wheat flour (CB-dough). Furthermore, the influence of simulated sweat on the electric response of such sensor was also investigated. Repeatable relationships in resistance versus strain were revealed and obtained for varying samples with different content of simulated sweat, in which the amplitude of resistance was directly proportional to the concentration of NaCl. Accordingly, the as-developed CB-dough sensor was efficaciously used for durable surveillance of human activity and real-time feedback of sweat secretion during body motion. This work offers a simple and cost-effective way to manufacture flexible strain sensors, with a broad application prospect in wearable electronics, artificial intelligence systems, and other bio-sensors.

Silicone-enhanced polyvinyl alcohol hydrogels for high performance wearable strain sensors

Flexible wearable strain sensors based on hydrogels have become a research hotspot in recent years due to their advanced application in many fields. Currently, most hydrogel-based strain sensors exhibit poor mechanical properties and low sensitivity. In this work, a conductive hydrogel as a wearable strain sensor was developed based on dual crosslinked polyvinyl alcohol (PVA) networks. The PVA was the main skeleton of the hydrogel and the water-soluble amino-polysiloxane (APSi) introduced into this hydrogel was the secondary network. The APSi and PVA were locked together by phytic acid (PA), which improved the microstructure and enhanced the mechanical properties of the hydrogel. This was mainly reflected in the higher tensile strength (1.27 MPa), elongation at break (425.5%), electrical conductivity (0.975 S/m), linearity (R2 = 0.999) and tensile strain sensitivity (gauge factor (GF) of 2.29). The tensile strength (0.166–1.270 MPa) and elongation (170.2–425.5%) of the hydrogel can be regulated continuously by adjusting the amount of APSi. These silicone-enhanced PVA hydrogels have good biocompatibility and hence can be used as wearable strain sensors.

Ultra-stable strain/ humidity dual-functional flexible wearable sensor based on brush-like AgNPs@CNTs@TPU heterogeneous structure

Wearable flexible sensors have a broad applications prospect in human motion and health monitoring. However, designing and manufacturing ultra-stable sensors with wide operating ranges and extremely low detection limits remain a challenging task. In this paper, a heterogeneous-structured fibrous membrane was constructed using the electrospinning process and subsequent ultrasonic homogenizer treatment. The fibrous membrane is composed of brush-like thermoplastic polyurethane (TPU) fibers, which are embedded with carbon nanotubes decorated with silver nanoparticles (AgNPs@CNTs). A dual-function sensor for strain and humidity based on the fiber membrane was designed. As a strain sensor, it has an ultra-low detection limit (0.05 %), an ultra-wide sensing range of 600 %, and excellent stability (100,000 cycles of stretch/release operation at 50 % strain). As a humidity sensor, it can achieve fast response as low as 1 s. With excellent sensing capabilities in terms of strain and humidity, the fiber membrane can be used to monitor breathing, pulse, and limb movement, as well as non-contact sensing, such as sensing the vibration of guitar strings or monitoring footsteps. The versatility and manufacturability of fiber membranes provide a new way for the application of wearable sensors in health monitoring and motion tracking.

Corrigendum to “Micro/nano-structure skeleton assembled with graphene for highly sensitive and flexible wearable sensor” [Compos. Part A Appl. Sci. Manuf. 165 (2023) 107357

Corrigendum to “Micro/nano-structure skeleton assembled with graphene for highly sensitive and flexible wearable sensor” [Compos. Part A Appl. Sci. Manuf. 165 (2023) 107357

Highly Stretchable and Stimulus-Free Self-Healing Hydrogels with Multiple Signal Detection Performance for Self-Powered Wearable Temperature Sensors

A flexible wearable temperature sensor is a novel electronic sensor that can monitor real-time changes in human body temperature in a variety of application scenarios and is regarded as the "crown jewel" of information collection technology. Although flexible strain sensors based on hydrogels have excellent self-healing effects and mechanical durability, their widespread application is still limited by external power sources. Herein, a novel self-energizing hydrogel was developed by embellishing cellulose nanocrystals (CNC) with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The resultant thermoelectrically conductive CNC was then employed as a booster for poly(vinyl alcohol) (PVA)/borax hydrogels. The obtained hydrogels exhibit remarkable self-healing performance (92.57%) and exceptional stretchability (989.60%). Additionally, the hydrogel was capable of accurately and reliably identifying human motion. Most importantly, it exhibits excellent thermoelectric performance, capable of generating stable and reproducible voltages. It shows a large Seebeck coefficient of 1.31 mV k-1 at ambient temperatures. When subjected to a temperature difference of 25 K, the output voltage reaches 31.72 mV. CNC-PEDOT:PSS/PVA conductive hydrogel is multifunctional with self-healing, self-powering, and temperature sensing, which has the potential to be used for the preparation of intelligent wearable temperature-sensing devices.

Liquid metal integrated PU/CNT fibrous membrane for human health monitoring.

Wearable flexible sensors are widely used in several applications such as physiological monitoring, electronic skin, and telemedicine. Typically, flexible sensors that are made of elastomeric thin-films lack sufficient permeability, which leads to skin inflammation, and more importantly, affects signal detection and consequently, reduces the sensitivity of the sensor. In this study, we designed a flexible nanofibrous membrane with a high air permeability (6.10mm/s), which could be effectively used to monitor human motion signals and physiological signals. More specifically, a flexible membrane with a point (liquid metal nanoparticles)-line (carbon nanotubes)-plane (liquid metal thin-film) multiscale conductive structure was fabricated by combining liquid metal (LM) and carbon nanotubes (CNTs) with a polyurethane (PU) nanofibrous membrane. Interestingly, the excellent conductivity and fluidity of the liquid metal enhanced the sensitivity and stability of the membrane. More precisely, the gauge factor (GF) values of the membrane is 3.0 at 50% strain and 14.0 at 400% strain, which corresponds to a high strain sensitivity within the whole range of deformation. Additionally, the proposed membrane has good mechanical properties with an elongation at a break of 490% and a tensile strength of 12MPa. Furthermore, the flexible membrane exhibits good biocompatibility and can efficiently monitor human health signals, thereby indicating potential for application in the field of wearable electronic devices.

Preparation of Thermoplastic Polyurethane/Multi-Walled Carbon Nanotubes Composite Foam with High Resilience Performance via Fused Filament Fabrication and CO2 Foaming Technique.

Wearable flexible sensors with high sensitivity and wide detection range are applied in motion detection, medical diagnostic result and other fields, but poor resilience and hysteresis remain a challenge. In this study, a high-resilience foam sensor was prepared through a combination of additive manufacturing and green physical foaming method. The conductive filaments were prepared by using MWCNTs-modified TPU by the physical method of melt blending. Samples were prefabricated using the FFF printer and then saturated with CO2 in an autoclave before being removed and heated to foam. The composite foam effectively reduced residual strain, demonstrating the high resilience of the 3D-printed composite materials with a foam porous structure. The residual strain of the sample before foaming was >6% after a single cycle, and then gradually increased. The residual strain of the foamed samples is less than 5%. In addition, composite foam has high sensitivity and can monitor subtle pressure changes (0~40 kPa). The sensing performance of the composite foam was evaluated, and the current signal remained stable under different loading rates and small compression strains (2~5%). By using this highly resilient conductive composite material, a hierarchical shoe insole was designed that successfully detected human walking and running movements.

Flexible Wearable Capacitive Sensors Based on Ionic Gel with Full-Pressure Ranges.

Flexible positive pressure sensors have been studied extensively and have been used in a lot of scenarios. However, negative pressure detection is also in demand in some scenarios, such as fluid mechanics analysis, air pressure sensing, and so on. Flexible wearable sensors that can detect both positive and negative pressures will greatly broaden the application field. In this paper, we report a flexible highly sensitive ionic gel (IG) pressure sensor, which is simple and of low cost to prepare and can reliably detect a large pressure range from -98 to 100 kPa under an atmospheric pressure of about 982 hPa. The IG dielectric layer is composed of polyvinyl alcohol and phosphoric acid with a random microstructure of sandpaper inversion. The sensor exhibits flexibility, cycling stability, and high sensitivity under both negative and positive pressures (S = 84.45 nF/kPa for the negative pressure section, S = 25.61 nF/kPa for the positive pressure section). These sensors could be worn on the body not only to test breathing and pulse but also to measure air pressure for estimating the altitude, showing that the flexible full-pressure sensors have a wider application range in wearable electronics.

Flexible Wearable Optical Sensor Based on Optical Microfiber Bragg Grating

Wearable sensing devices, which can find tremendous applications in healthcare and automation, are attracting great attention in recent years. Herein, we report a flexible wearable optical sensor (FWOS) which consists of the microfiber Bragg grating ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mu }$</tex-math></inline-formula> FBG) as the core sensing node and a ductile PDMS film as the sensor encapsulation. Due to the strain amplification effect of the microfiber, the sensitivity of FWOS to pressure, bending angle and temperature is significantly enhanced to 0.03 nm/kPa, 0.19 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> and 0.04 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, respectively. Furthermore, thanks to the better flexibility of the microfiber structure, the FWOS device could be achieved for real-time monitoring of wrist pulses, finger knuckle bending, and human body temperature. The proposed FWOS creates new ideas for the development of future wearable optical devices, which is critical for the advancement of next-generation robotics, and healthcare monitoring.

Environment-tolerant versatile ion-conductive eutectic hydrogels for self-powered wearable flexible sensors

Conductive hydrogels (CHs) have been widely utilized in the design of wearable flexible sensors. The remaining issues with CHs include their propensity to dehydrate in the open air and freeze at low temperatures, which makes them significantly less functional. Additionally, the wide applications of CHs are limited by their dependence on external power sources and inadequate sensing of humidity, strain, etc. Herein, a series of versatile ion-conductive adhesive hydrogels (GAAAD) with emblematic on-demand 3D cross-network structures were nanoengineered by combining solvent exchange strategies with in-situ physical and covalent cross-linking. The GAAAD possesses exceptional properties such as integrated outstanding sensing of multiple external stimuli in harsh environments, desirable adhesive ability towards various substrates, mechanical robustness, transparency, anti-freezing and anti-dehydration performance, and self-healing capacity. Even after being frozen at −20 ℃ for 48 h, GAAAD could be utilized for effective real-time human sleeping monitoring, demonstrating preponderant environmental stability. Integrated with the versatile origins of GAAAD, a simple Cu/GAAAD/Zn self-powered flexible sensor (GAAADB) was developed based on the fundamental structure of a primary battery, which exhibits remarkable properties of stable open-circuit voltage even in extremely cold environments, sensitive response to applied tensile or compressive strain, as well as its repeatability and durability. Interestingly, based on the sensing mechanism of the potential difference between the humidity-regulating electrodes, GAAADB was substantiated to be reliable for long-term respiratory monitoring (with the humidity response/recovery time less than 1 s) under extreme cold conditions (−20 °C), indicating its great potential for extensive applications in respiratory diagnosis, sleep monitoring, electronic skin, and wearable electronics.

Ultra-stretchable, high-adhesive, self-healable and remoldable hydrogel sensor with dynamic multi-interactions for multiscale motion detection, Braille transmission and temperature monitoring

Flexible wearable electronic sensor has attracted considerable interest due to their inherent advantages, but the multifield and high-precision applications require the development of unique and multifunctional material systems. Herein, carboxymethyl chitosan (CMCS)/sodium alginate (SA)/zwitterionic copolymer (SHA)/4-formylphenylboronic acid (Bn) ionic conductive hydrogel (CSSB) was designed and fabricated by a facile one-pot blending strategy with CMCS and SA as the gel matrix, SAH as the conductive filler and Bn as the dynamic crosslinker. CSSB ionic hydrogel exhibits outstanding mechanical, self-healing, remodeling and electrochemical properties (ultra-high stretchability of 23600%, fracture toughness of 7.01 MJ m−3, 96.6% strain self-healing efficiency at 30 °C for 15 min and electrical conductivity of 3.656 S/m) to satisfy the requirements of various application scenarios. The flexible wearable sensor based on the CSSB ionic hydrogel is demonstrated, and the excellent strain sensing properties endow the sensor to monitor multiscale human movements and to transmit Braille information. Moreover, the sensor can be designed as a temperature sensor with unique thermal sensitivity (-4.48%/°C), outstanding detection accuracy (R2 = 0.9988) and an extremely low detection limit (0.1 °C) for monitoring changes in human body temperature and variations in storage temperature during long distance transport. This work is expected to provide ideas for the next generation of environmental multi-sensory electronic skin and temperature detection electronics.

One-pot strategy to fabricate conductive cellulose nanocrystal-polyethylenedioxythiophene nanocomposite: Synthesis mechanism, modulated morphologies and sensor assembly

Simple preparation, good conductivity, and excellent hydrophilicity are in urgent demand due to fast growth of wearable intelligent devices. Cellulose nanocrystal-polyethylenedioxythiophene (CNC-PEDOT) nanocomposites with modulated morphology were prepared through Iron (III) p-toluenesulfonate hydrolysis of commercialized microcrystalline cellulose (MCC) and in situ polymerization of 3,4-ethylenedioxythiophene monomers (EDOT) through one-pot green synthesis, where preparation and modification of CNC were obtained for uses as templates to anchor PEDOT nanoparticles. The resultant CNC-PEDOT nanocomposite gave well-dispersed PEDOT nanoparticles with sheet-like structure on the CNC surface, possessing higher conductivity and improved hydrophilicity or dispersibility. Subsequently, a wearable non-woven fabrics (NWF) sensor was successfully assembled by dipping the conductive CNC-PEDOT, and showed excellent sensing response for multiple signals (subtle deformation from various human activities and temperature). This study provides a feasible and large-scale production of CNC-PEDOT nanocomposites and their applications in wearable flexible sensors and electronic devices.

Pt/MXene-Based Flexible Wearable Non-Enzymatic Electrochemical Sensor for Continuous Glucose Detection in Sweat.

Wearable non-invasive sensors facilitate the continuous measurement of glucose in sweat for the treatment and management of diabetes. However, the catalysis of glucose and sweat sampling are challenges in the development of efficient wearable glucose sensors. Herein, we report a flexible wearable non-enzymatic electrochemical sensor for continuous glucose detection in sweat. We synthesized a catalyst (Pt/MXene) by the hybridization of Pt nanoparticles onto MXene (Ti3C2Tx) nanosheets with a broad linear range of glucose detection (0-8 mmol/L) under neutral conditions. Furthermore, we optimized the structure of the sensor by immobilizing Pt/MXene with a conductive hydrogel to enhance the stability of the sensor. Based on Pt/MXene and the optimized structure, we fabricated a flexible wearable glucose sensor by integrating a microfluidic patch for sweat collection onto a flexible sensor. We evaluated the utility of the sensor for the detection of glucose in sweat, and the sensor could detect the glucose change with the replenishment and consumption of energy by the body, and a similar trend was observed in the blood. An in vivo glucose test in sweat indicated that the fabricated sensor is promising for the continuous measurement of glucose, which is essential for the treatment and management of diabetes.

Real-time monitoring flexible hydrogels based on dual physically cross-linked network for promoting wound healing

To achieve smart and personalized medicine, the development of hydrogel dressings with sensing properties and biotherapeutic properties that can act as a sensor to monitor of human health in real-time while speeding up wound healing face great challenge. In the present study, a biocompatible dual-network composite hydrogel (DNCGel) sensor was obtained via a simple process. The dual network hydrogel is constructed by the interpenetration of a flexible network formed of poly(vinyl alcohol) (PVA) physical cross-linked by repeated freeze-thawing and a rigid network of iron-chelated xanthan gum (XG) impregnated with Fe3+ interpenetration. The pure PVA/XG hydrogels were chelated with ferric ions by immersion to improve the gel strength (compressive modulus and tensile modulus can reach up to 0.62 MPa and 0.079 MPa, respectively), conductivity (conductivity values ranging from 9 × 10−4 S/cm to 1 × 10−3 S/cm) and bacterial inhibition properties (up to 98.56%). Subsequently, the effects of the ratio of PVA and XG and the immersion time of Fe3+ on the hydrogels were investigated, and DNGel3 was given the most priority on a comprehensive consideration. It was demonstrated that the DNCGel exhibit good biocompatibility in vitro, effectively facilitate wound healing in vivo (up to 97.8% healing rate) under electrical stimulation, and monitors human movement in real time. This work provides a novel avenue to explore multifunctional intelligent hydrogels that hold great promise in biomedical fields such as smart wound dressings and flexible wearable sensors.