A temperature and pressure dual-responsive, stretchable, healable, adhesive, and biocompatible carboxymethyl cellulose-based conductive hydrogels for flexible wearable strain sensor

Advanced development of smart stimulus-responsive cellulose-based composites through polymer science and nanoscale engineering: Preparation approaches and applications

With the advancement of intelligent materials and technology, cellulose offers notable advantages, such as high mechanical strength, good degradability, and high sensor sensitivity, making it one of the most promising stimulus-responsive materials. Stimulus-responsive cellulose-based composites have garnered significant attention due to their unique benefits in environmental adaptability, functionality, and sustainability. The aim of this review is to highlight the preparation methods, stimulus-responsive types, and promising applications of cellulose-based composites. We reviewed the preparation methods of stimulus-responsive cellulose-based composites including cellulose/MXene composites, cellulose/GO composites, cellulose/carbon nanotube composites, cellulose/inorganic nano-functional composites. Moreover, we also discussed the stimulus-responsive types (such as light stimulation, electrical stimulation, humidity stimulation, magnetic stimulation, dual/multiple stimulation) and potential applications (such as wearable devices, smart fabric, energy field, biomedical field). This review aims to provide a comprehensive review of the current research status of stimulus-responsive cellulose-based composites, with the intention of offering valuable insights and references for researchers in related fields.

Ultrastretchable, Antifreeze, Self-Healing, Conductive Hydrogel-Based Triboelectric Nanogenerators for Human Motion Detection and Signal Transmission

Wearable electronic devices based on conductive hydrogels have gained attention for applications in health monitoring, electronic skin, and human-computer interaction. However, limited functionality hinders the development of conventional hydrogels. Herein, a multifunctional poly(acrylic acid)/carboxymethyl cellulose/polydopamine-ethylene glycol (PAA/CMC/PDA-EG) hydrogel is developed via free radical polymerization initiated by a PDA-Fe3+ redox system and dynamic metal coordination. The hydrogel exhibits excellent mechanical properties (tensile strength, 71 kPa; elongation, 872%), strong adhesion, self-healing ability, and environmental tolerance (nonfreezing at -15 °C). It functions as a strain sensor with a wide working range (0-500%) and high sensitivity (GF = 10.49), suitable for human motion detection. As an electrode in a triboelectric nanogenerator (TENG), the hydrogel delivers stable electrical output (open-circuit voltage: 100 V), powering small electronics and enabling signal transmission. This work provides a reference for the development of multifunctional hydrogel-based flexible electronics and self-powered devices.

A Printable Deep Eutectic/Copper Conductive Colloid for Wearable Devices

The advancement of wearable electronics has placed higher demands on the comfort and convenience of flexible materials. In this work, a conductive pseudoplastic colloid was developed by utilizing the oxygen elements adsorbed on the surface of copper powder, which forms donor-acceptor interactions with the hydrogen bond donors in a deep eutectic solvent. The flakelike copper powder, serving as a conductive filler, provides more efficient spatial conductive pathways and further enhances the cross-linking ability between the copper powder and the deep eutectic solvent. The resulting deep eutectic/copper colloid not only exhibits low volume resistivity (1.19 × 10-3 (Ω·m)), high viscosity, and excellent thermal stability but also demonstrates outstanding strain-resistance characteristics. By printing onto a textile substrate, a flexible strain sensor with a wide linear strain range (5-90%) and ultrahigh sensitivity (gauge factor ≈ 1 × 105) was fabricated. This sensor can sensitively and stably detect human body movements such as joint and muscle motions. Furthermore, the sensor has been integrated into a portable glove for motion detection and human-machine interaction, showcasing its great potential as a high-performance wearable strain sensor.

An ultrasensitive flexible biosensor enabled by high-performance graphene field-effect transistors with defect-free van der Waals contacts for breast cancer miRNA fast detection

MicroRNAs (miRNAs) present in bodily fluids such as blood, saliva, and urine hold significant potential for both diagnosing and prognosing breast cancer. However, the development of flexible wearable field-effect transistor (FET) breast cancer miRNA biosensors still faces many challenges. Herein, we developed an ultrasensitive flexible biosensor based on a high-performance FET with defect-free van der Waals contacts for breast cancer miRNA fast detection. The flexible biosensor achieves a limit of detection (LOD) as low as 1.92 fM, a wide linear detection range of 10 fM-100 pM, and a short detection time of 10 min for fast detection of miRNA-155, which is approximately a 5-fold lower LOD compared to conventional graphene FET biosensors. Additionally, the sensor maintains stable sensing performance even after 100 bending/relaxation cycles. The defect-free graphene channel and excellent electrical properties of the flexible FET contribute to the high performance of the biosensor. The biosensor effectively differentiates miRNA levels in serum between breast cancer patients and healthy individuals, proving the possibility of practical application. It also successfully detects miRNA in sweat by attaching the biosensor to the human body, demonstrating its promise for non-invasive health monitoring as a wearable device. This easy-to-fabricate, high-performance flexible biosensor advances cancer biomarker analysis and wearable health monitoring technology.

A highly stretchable, self-adhesive, anti-freezing dual-network conductive carboxymethyl chitosan based hydrogel for flexible wearable strain sensor

Achieving the integration of multiple properties in a single hydrogel system faces significant challenges. This research presents a simple approach to developing a multifunctional conductive hydrogel with high stretchability (>740 %), electrical conductivity, frost resistance and self-adhesiveness. It serves as a wearable, flexible electronic material, it remains functional even in low-temperature environments. The hydrogel is synthesized by incorporating a uniformly mixed solution of carboxymethyl cellulose (CMC) and aminated carbon nanotubes (NH2-CNTs) into a polyacrylamide (PAM)/gelatin dual-network hydrogel. By adjusting the CMC mass fraction, the optimal composite hydrogel is obtained within a specified gradient. After cross-linking modification with a calcium chloride (CaCl2) solution, enhances its mechanical properties, resulting in a final hydrogel with excellent stretchability (strain = 749 %), strong adhesion, frost resistance, moisture retention, and conductivity. Additionally, this research explores the hydrogel's potential for anti-counterfeiting and salt ion monitoring by analyzing changes in mechanical properties and transparency. The hydrogel exhibits high sensitivity to external strains and effectively monitors human signals such as finger bending, head movement, and speech, even at low temperatures. This research provides new insights into flexible electronic skin, wearable sensors and human-computer interaction, expanding the potential applications of multifunctional conductive hydrogels.

Ultrafast fabrication of ε-polylysine/amide-modified chitin-based conductive hydrogel with self-healing, adhesive and antibacterial abilities as a wearable strain sensor

In the realm of health monitoring, wearable electronic devices that utilize conductive hydrogels have garnered considerable attention. Nonetheless, the formidable challenge persists in streamlining the intricate preparation process and formulating a conductive hydrogel that seamlessly integrates diverse functionalities. In this study, we propose a strategy to fabricate multifunctional wearable hydrogel-based strain sensors (ε-PL/AMC-Al) in an ultrafast manner. Amide-modified chitin (AMC) was synthesized homogeneously, thereafter, Al3+ ions and ε-Polylysine (ε-PL) were introduced to interact with AMC through physical cross-linking techniques to form a three-dimensional network. Favorable mechanical and self-healing properties were achieved through the presence of multiple noncovalent interactions. The incorporation of ε-PL imparted antibacterial properties to the hydrogel sensor, thereby safeguarding it against bacterial contamination. Importantly, the incorporation of Al3+ not only facilitated the gelation process but also imparted electrical conductivity to the hydrogel, enabling it to function as a strain sensor. Notably, the adhesive property of the ε-PL/AMC-Al hydrogel ensured intimate contact, thereby allowing it to accurately monitor and differentiate between both gross and subtle human body movements without compromising its long-term stability. Based on its straightforward manufacturing process and versatility, the as-prepared hydrogel sensor exhibits significant potential for a diverse array of large-scale applications, including wearable electronic devices.

A Strain Sensor for Multidirectional Deformation Detection Realized by Rolling Patterned Vertically Aligned Carbon Nanotubes

Flexible and stretchable sensors have garnered significant attention in the fields of human-computer interaction, motion capture, and health monitoring. Presently, most sensors are limited to capturing motion in a single direction and lack the capability to analyze multidirectional deformations in real world. A single device capable of detecting multidirectional deformations has always been a high expectation and a daunting challenge. In this work, we realize the idea of using a single sensor for multidirectional sensing by adopting a "one-step" rolling process to transfer vertically aligned carbon nanotubes grown on a silicon wafer onto a flexible Ecoflex substrate. The entire preparation process is simple and efficient. Distinct conductive paths form along different directions controlled by the rolling process and the pattern design of carbon nanotubes, thus resulting in a sensitive directional dependence. The sensor exhibits remarkable performance, including a wide operating range (0-120%), high sensitivity (GF = 126.6), short response time (64 ms), and good stability (over 4000 cycles under strain 40%). The sensors are demonstrated for detecting motion signals and monitoring human health, ranging from subtle motion signals to large deformation. These sensor characteristics fulfill the requirements of various practical scenarios and have an immense potential for applications in human-computer interaction interfaces, intelligent robots, and in situ health monitoring.

Gelatin and zinc ion-cooperated triple crosslinked hydrogels with high mechanical properties and ultrasensitivity for multimodal sensing and handwriting recognition

With the rapid development of flexible electronics technology, high-performance flexible sensors have shown great potential in wearable devices and human-computer interaction fields. In this study, a hydrogel (PMAGZ) reinforced by gelatin and Zn2+ was prepared using a one-pot method, which formed a triple-bonded cross-linked network structure through covalent, hydrogen, and ligand bonds to exhibit excellent mechanical properties and sensing characteristics, and can be applied to multimodal sensors and handwriting recognition. The introduction of gelatin and Zn2+ strengthens the cross-linked structure inside the hydrogel, which can effectively improve the tensile strength, strain, and toughness of the hydrogel. Additionally, the addition of ethylene glycol and lithium chloride endowed the hydrogel with good frost resistance and electrical conductivity. The PMAGZ hydrogel sensor has a fast response time, high sensitivity, wide sensing range, and excellent fatigue resistance, and is capable of accurately monitoring human movements and handwriting information. Combined with machine learning algorithms (ML), the sensor can effectively recognize different handwritten letters with an accuracy of 99.8 %. This study provides a new approach for developing high-performance, multifunctional flexible sensors, which have broad application prospects in flexible wearable devices and human-computer interaction fields.

A biomass-derived multifunctional conductive coating with outstanding electromagnetic shielding and photothermal conversion properties for integrated wearable intelligent textiles and skin bioelectronics

Intelligent electronic textiles have important application value in the field of wearable electronics due to their unique structure, flexibility, and breathability. However, the currently reported electronic textiles are still challenged by issues such as their biocompatibility, photothermal conversion, and electromagnetic wave contamination. Herein, a multifunctional biomass-based conductive coating was developed using natural carboxymethyl starch (CMS), dopamine and polypyrrole (PPy) and then further employed for constructing multifunctional intelligent electronic textiles. The prepared textiles had excellent water resistance, breathability, antioxidant and antibacterial activities, electromagnetic shielding (33 dB) as well as photothermal conversion performance, and stability. Notably, the fabricated textile could be heated from room temperature to 55 °C within 10 s under infrared radiation, and then the surface temperature of the textile could be reduced to 40 °C (τs = 42.05 s) within 20 s, holding great significance for research on new wearable photothermal textiles. Furthermore, the textile was utilized as a skin strain sensor, demonstrating high sensitivity to temperature, strain, photothermal and bioelectric signals and motion detection. It could monitor the physiological signal, motion control, and body temperature change of the human body in real time, offering significant potential to be applicable to integrated wearable intelligent textiles and skin bioelectronics.

One-step fabrication of dual-network cellulose-based hydrogel sensors with high flexibility and conductivity under ZnCl2 solvent method for flexible sensing properties

Flexible smart sensing materials are gaining tremendous momentum in wearable and bionic smart electronics. To satisfy the growing demand for sustainability and eco-friendliness, biomass-based hydrogel sensors for green and biologically safe wearable sensors have attracted significant attention. In this work, we have prepared MCC/PAA/AgNWs/CNTs hydrogel sensors with excellent conductive sensing properties by a simple physical blending method. The ZnCl2 solvent system was used to dissolve the MCC, followed by introducing acrylic acid to polymerize under UV illumination. Subsequently, CNTs and AgNWs were introduced into the hydrogel network to obtain hydrogel with excellent conductive sensing and antibacterial properties. Here, the physical and chemical interactions between the components significantly improved the mechanical properties of the hydrogels, exhibiting good tensile strength (0.45 MPa), elongation at break (558 %) and adhesion properties. Hydrogel presented outstanding electrical conductivity and significantly elongation sensitive (GF = 4.73 when elongated 90-120 %). Additionally, the hydrogel was also found to have significant antimicrobial activity against both Escherichia coli and Staphylococcus aureus, and the antibacterial effect was almost 100 %. With high sensitivity, stability, and reproducibility, these hydrogel strain transducers can detect various human movements, including finger flexion, wrist movement, joint motion, and heartbeat.

Stretchable and self-healing carboxymethyl cellulose/polyacrylic acid conductive hydrogels for monitoring human motions and electrophysiological signals

Stretchable conductive hydrogels have attracted great attention in flexible electronics. Nevertheless, conductive hydrogels would suffer from an inevitable damage during use, significantly reducing the reliability and limiting the practicability. Herein, stretchable and self-healing conductive hydrogels are designed form carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and Fe3+, which are applied for monitoring human motions and electrophysiological signals. The plentiful H-bonding and metal coordination endow the conductive hydrogels with good mechanical (fracture strain: 917 %; fracture stress: 202 kPa; toughness: 1.1 MJ m-3) and self-healing properties. After self-healing, the fracture stress is almost fully recovered, the fracture strain is restored to 72 %, and the conductivity is reestablished to 98 %. The conductive hydrogels show good fatigue resistance during cyclic tensile and compressive loading-unloading tests. Furthermore, the mechanical deformation would lead to the resistance change of the hydrogel to realize the electrical signal record. So, the hydrogel was assembled into a flexible wearable sensor that has good electrical conductivity (0.779 S m-1), fast responsiveness (response time: 300 ms; recovery time: 200 ms) and high sensitivity (gauge factor (GF) = 7.99, 400-650 %). This work demonstrates a simple and efficient strategy for developing stretchable and self-healing conductive hydrogels in healthcare monitoring and flexible electronics.

A flexible wearable sensor based on the multiple interaction and synergistic effect of the hydrogel components with anti-freezing, low swelling for human motion detection and underwater communication

To meet the increasing demand for wearable sensor in special environment such as low temperature or underwater, a multifunctional ionic conducting hydrogel (Gel/PSAA-Al3+ hydrogel) with anti-freezing and low swelling for human motion detection and underwater communication was prepared using gelatin (Gel), [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA), acrylamide (AAm), acrylic acid (AAc), and AlCl3. Due to reversible hydrogen bonding, electrostatic interactions and metal coordination crosslinking between the polymer networks, the resulting Gel/PSAA-Al3+ hydrogels present low swelling property in water and exhibit large tensile properties (~1050 %), high tensile strength (~250 kPa) and excellent fatigue resistance. In addition, the hydration capacity of SBMA and AlCl3 endows the Gel/PSAA-Al3+ hydrogel fantastic anti-freezing (-31.58 °C) and water retention properties. Moreover, the electrostatic interaction between SBMA and AlCl3 due to the ion hopping mechanism endows the hydrogel with excellent ionic conductivity (6.38 mS/cm). The Gel/PSAA-Al3+ hydrogel sensors present good biocompatibility and provide a wide operating range (0 %-1050 %), fast response time (229 ms) and recovery time (248 ms), high sensitivity (GF = 1.61) and excellent stability for detecting large and small body movements. The Gel/PSAA-Al3+ hydrogel shows potential applications as a wearable sensor for communication at low temperature or underwater.

Biomaterials for reliable wearable health monitoring: Applications in skin and eye integration

Recent advancements in biomaterials have significantly impacted wearable health monitoring, creating opportunities for personalized and non-invasive health assessments. These developments address the growing demand for customized healthcare solutions. Durability is a critical factor for biomaterials in wearable applications, as they must withstand diverse wearing conditions effectively. Therefore, there is a heightened focus on developing biomaterials that maintain robust and stable functionalities, essential for advancing wearable sensing technologies. This review examines the biomaterials used in wearable sensors, specifically those interfaced with human skin and eyes, highlighting essential strategies for achieving long-lasting and stable performance. We specifically discuss three main categories of biomaterials-hydrogels, fibers, and hybrid materials-each offering distinct properties ideal for use in durable wearable health monitoring systems. Moreover, we delve into the latest advancements in biomaterial-based sensors, which hold the potential to facilitate early disease detection, preventative interventions, and tailored healthcare approaches. We also address ongoing challenges and suggest future directions for research on material-based wearable sensors to encourage continuous innovation in this dynamic field.

High-performance conductive double-network hydrogel base on sodium carboxymethyl cellulose for multifunctional wearable sensors

Sodium carboxymethyl cellulose showed great potential in wearable intelligent electronic devices due to its low price and good biocompatibility. This research aimed to develop a novel conductive hydrogel with stretchable, self-healing, self-adhesive, antibacterial, 3D printable properties, for the development of multifunctional flexible electronic materials based on sodium carboxymethyl cellulose. A multifunctional conductive hydrogel based on sodium carboxymethyl cellulose (SCMC) was synthesized by simple polymerization of SCMC, acrylic acid (AA) and alkaline calcium bentonite (AC-Bt). The multifunctional hydrogels (PAA-SCMC) possess excellent mechanical property (stress: 0.25 MPa; strain: 1675.0 %), Young's modulus (75.6 kPa), and conductivity (2.25 S/m). The multifunctional PAA-SCMC hydrogels serve as strain sensors (Gauge Factor (GF) = 12.68), temperature sensors (temperature coefficient of resistance (TCR) = -0.887 % °C at 20 °C-60 °C), sweat sensors, and pressure sensors. Importantly, the obtained hydrogels exhibited exceptional self-healing capability, self-adhesive properties, antimicrobial properties and 3D printability. The printed hydrogel has good mechanical properties, conductivity and antibacterial properties. Moreover, the hydrogel sensor possessed prominent sensitivity and cyclic stability to accurately monitor human motion, emotional changes, physiological signals in real time, and a hydrogel-based flexible touch keyboard was also fabricated to recognize writing trajectories. Overall, this study provided novel insights into the simple and efficient synthesis and sustainable manufacturing of environmentally friendly multifunctional flexible electronic skin sensors.

Revolutionizing human healthcare with wearable sensors for monitoring human strain

With the rapid advancements in wearable sensor technology, healthcare is witnessing a transformative shift towards personalized and continuous monitoring. Wearable sensors designed for tracking human strain offer promising applications in rehabilitation, athletic performance, occupational health, and early disease detection. Recent advancements in the field have centered on the design optimization and miniaturization of wearable biosensors. Wireless communication technologies have facilitated the simultaneous, non-invasive detection of multiple analytes with high sensitivity and selectivity through wearable biosensors, significantly enhancing diagnostic accuracy. This review meticulously chronicles noteworthy advancements in wearable sensors tailored for healthcare and biomedical applications, spanning the current market landscape, challenges faced, and prospective trends, including multifunctional smart wearable sensors and integrated decision-support systems. The domain of flexible electronics has witnessed substantial progress over the past decade, particularly in flexible strain sensors, which are crucial for contemporary wearable and implantable devices. These innovations have broadened the scope of applications in human health monitoring and diagnostics. Continuous advancements in novel materials and device architectural methodologies aim to expand the utility of these sensors while meeting the increasingly stringent demands for enhanced sensing performance. This review explores the diverse array of wearable sensors-from piezoelectric, piezoresistive, and capacitive sensors to advanced optical and bioimpedance sensors-each distinguished by unique material properties and functionalities. We analyzed these technologies' sensitivity, accuracy, and response time, which were crucial for reliably capturing strain metrics in dynamic, real-world conditions. Quantitative performance comparisons across various sensor types highlighted their relative effectiveness, strengths, and limitations regarding detection precision, durability, and user comfort. Additionally, we discussed the current challenges in wearable sensor design, including energy efficiency, data transmission, and integration with machine learning models for enhanced data interpretation. Ultimately, this review emphasized the revolutionary potential of wearable strain sensors in advancing preventative healthcare and enabling proactive health management, ushering in an era where real-time health insights could lead to more timely interventions and improved health outcomes.

Biodegradable, robust, and conductive bacterial cellulose @PPy-P macrofibers as resistive strain sensors for smart textiles

Fiber-based resistive strain sensors have attracted significant interest in the development of smart wearable devices due to their portability, flexibility, and easy conformability. However, current fiber-based resistive strain sensors mainly composed of metals and nondegradable polymers are not environmentally friendly and have poor mechanical strength. In this work, we examined biodegradable, robust, and conductive macrofibers fabricated through the in situ polymerization of p-toluenesulfonic acid (P-TSA)-doped polypyrrole (PPy) in bacterial cellulose (BC) nanofibers using wet-stretching and wet-twisting methods. The BC/PPy-P macrofibers possessed excellent conductivity (~7.19 S/cm), with superior mechanical properties (~210 MPa tensile strength and 2 GPa Young's modulus). Importantly, the BC/PPy-P microfiber operating as a resistive strain sensor possessed fast response time (15 s) and long-term stability (up to 1000 cycles), which could be used to effectively detect human movements. Moreover, the matrix material BC of BC/PPy-P macrofibers could be completely degraded within 96 h in the cellulase solution, leaving only PPy-P particles that could be recycled for other use. Therefore, the prepared BC/PPy-P microfibers provided a promising strategy for developing green resistive strain sensing fibers, with great potential to design eco-friendly smart fabric for monitoring human movements.

Starch/polyacrylamide hydrogels with flexibility, conductivity and sensitivity enhanced by two imidazolium-based ionic liquids for wearable electronics: Effect of anion structure

To meet the growing demands for sustainable and eco-friendly wearable electronics, biopolymer-based hydrogels have attracted much attention. As one of the most abundant sources of biopolymers, starch has the advantages of low-cost, renewability, biocompatibility and biodegradability. However, mechanical fragility, low conductivity and low sensitivity limited the application of starch-based hydrogels. Herein, two imidazolium-based ionic liquids with different anions (chloridion and acetate) were introduced into corn starch/polyacrylamide hydrogels. The mechanical properties (the maximum elongation: 515.4 %), conductivity (the maximum value: 3.1 S·m-1) and sensitivity (the maximum gauge factor value: 9.3) of the hydrogel were enhanced by the two ionic liquids and proved by the microcosmic characterizations and theoretical simulations (DFT). The two ionic liquids varied in their impacts on the above properties of the hydrogels due to the different anion structure. In mechanical properties, acetate was dominant over chloridion, while the opposite was true for conductivity. Based on the above properties of the starch-based hydrogels, wearable electronics were constructed for detecting human joint motions, subtle expressions, temperature and touch screen operations. This work not only provides novel starch-based hydrogels as candidates for the wearable electronics, but also lays a theoretical foundation for the application of ionic liquids in biopolymer-based materials.

Flexible Pressure, Humidity, and Temperature Sensors for Human Health Monitoring

The rapid advancements in artificial intelligence, micro-nano manufacturing, and flexible electronics technology have unleashed unprecedented innovation and opportunities for applying flexible sensors in healthcare, wearable devices, and human-computer interaction. The human body's tactile perception involves physical parameters such as pressure, temperature, and humidity, all of which play an essential role in maintaining human health. Inspired by the sensory function of human skin, many bionic sensors have been developed to simulate human skin's perception to various stimuli and are widely applied in health monitoring. Given the urgent requirements for sensing performance and integration of flexible sensors in the field of wearable devices and health monitoring, here is a timely overview of recent advances in pressure, humidity, temperature, and multi-functional sensors for human health monitoring. It covers the fundamental components of flexible sensors and categorizes them based on different response mechanisms, including resistive, capacitive, voltage, and other types. Specifically, the application of these flexible tactile sensors in the area of human health monitoring is highlighted. Based on this, an extended overview of recent advances in dual/triple-mode flexible sensors integrating pressure, humidity, and temperature tactile sensing is presented. Finally, the challenges and opportunities of flexible sensors are discussed.

Hydrogel-based bimodal sensors for high-sensitivity independent detection of temperature and strain

Avoiding crosstalk between strain and temperature detection is crucial for bimodal hydrogel sensors, yet achieving high sensitivity for both parameters while maintaining signal decoupling remains a significant challenge. In this study, a bimodal sensor was developed by locally coating poly (3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT: PSS) onto the hydrogel surface, creating distinct regions for strain and temperature detection. These regions form localized strain concentration zones and wrinkle structures, respectively. The localized strain concentration enhances the sensor's sensitivity from 8.5 to 18.5. Additionally, the sensor demonstrates a low detection limit (0.2 %), a wide detection range (up to 1356 %), a fast response time, and excellent cyclic stability for strain measurements. The temperature detection region, leveraging the thermoelectric effect, improves the Seebeck coefficient of the PEDOT: PSS coating from 20 to 122.86 μVK-1 through de-doping and energy band modulation. Moreover, the temperature sensing of the PEDOT: PSS coating features good cyclic stability, a rapid response time, and versatile testing capabilities. This innovative structural design effectively decouples strain and temperature signals across a broad strain range (0-600 %). These sensors hold potential applications in human health monitoring and as electronic skin for flexible robotics.

Eco-friendly property modulation of biobased gels of carboxymethyl cellulose-integrated poly(tertiary amine)s for the removal of azo-food dyes

Anionic polysaccharide-based gels enable the design of biobased materials with biochemical properties, non-toxic and natural origin. A new set of cationic gels was prepared from carboxymethylcellulose (CMC)-doped tertiary amino functional cationic monomers 2-(dimethylamino)ethyl methacrylate and N-(3-(dimethylamino)propyl) methacrylamide via the formation of semi-interpenetrated network (semi-IPN) at different polymerization temperatures, Tprep. A detailed understanding of the temperature-dependent synthesis and physicochemical response is required for the design of interpenetrating networks with CMC as an adsorbent that provides effective sources for the removal of azo-food dyes such as tartrazine and carmoisine from aqueous solutions. The variation of elasticity and swelling properties with respect to polymerization temperature was investigated. CMC-integration and polymerization temperature played a decisive role in the compressive elasticity. Incorporation of CMC into copolymer matrix led to a significant increase in elasticity of semi-IPNs, while mechanically weaker gels were obtained with increasing Tprep. Addition of CMC increased the swelling modulus of semi-IPNs formed at -18 °C by 2.6-fold. While the transparency changed depending on Tprep and microstructure, addition of CMC decreased the swelling rate of gels at all polymerization temperatures. The compressive modulus decreased with the swelling process in accordance with the Rubber elasticity theory. Semi-IPN gels showed stable swelling against pH-change in aqueous solutions and exhibited excellent pH-sensitivity significantly in low pH. A 4 to 12 fold decrease in maximum volume was observed by varying the pH between 2.1 and 9.8. The correlation between polymerization temperature and removal of azo-food dyes; tartrazine and carmoisine from contaminated wastewater with CMC-based gels was studied. Dynamic adsorption equilibrium was reached in 30 min, and tartrazine and carmoisine removal performances varied between 92.8 % and 98.4 %. respectively. The adsorption data for azo-dyes were evaluated by Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlich-Patterson, Sips, and Tooth isotherm models, but were best described by Langmuir and Redlich-Patterson models as they gave the highest correlation. Pseudo-first order, pseudo-second order, Elovich, Avrami kinetic and intra-particle diffusion models were investigated and dye adsorption was represented by pseudo-second-order model. After the adsorption process, semi-IPNs can easily be regenerated and effectively reused over five cycles. The study provided new insights towards the facile and sustainable synthesis of eco-friendly multifunctional CMC-based gels carrying tertiary amino groups for effective removal of azo-based food colorants.

Wide-humidity, anti-freezing and stretchable multifunctional conductive carboxymethyl cellulose-based hydrogels for flexible wearable strain sensors and arrays

Hydrogels play an important role in the design and fabrication of wearable sensors with outstanding flexibility, high sensitivity and versatility. Since hydrogels lose and absorb water during changes in humidity and temperature, it is critical and challenging to obtain hydrogels that function properly under different environmental conditions. Herein, a dual network hydrogel based on tannic acid (TA) reinforced polyacrylamide (PAM) and sodium carboxymethylcellulose (CMC) was constructed, while the introduction of the green solvents Solketal and LiCl endowed the hydrogel with greater possibilities for further modification to improve the water content and consistency of the mechanical properties over 30-90 % RH. This composite hydrogel (PTSL) has long-term stability, excellent mechanical strength, and freezing resistance. As strain sensors, they are linear over the entire strain range (R2 = 0.994) and have a high sensitivity (GF = 2.52 over 0-680 % strain range). Furthermore, the hydrogel's exceptional electrical conductivity and freezing resistance are a result of the synergistic effect of Solketal and LiCl, which intensifies the contact between the water molecules and the colloidal phase. This research could address the suitability of hydrogels over a wide range of humidity and temperature, suggesting great applications for smart flexible wearable electronics in harsh environmental conditions.

Ureido-Ionic Liquid Mediated Conductive Hydrogel: Superior Integrated Properties for Advanced Biosensing Applications

Ionic conductive hydrogels (ICHs) have recently gained prominence in biosensing, indicating their potential to redefine future biomedical applications. However, the integration of these hydrogels into sensor technologies and their long-term efficacy in practical applications pose substantial challenges, including a synergy of features, such as mechanical adaptability, conductive sensitivity, self-adhesion, self-regeneration, and microbial resistance. To address these challenges, this study introduces a novel hydrogel system using an imidazolium salt with a ureido backbone (UL) as the primary monomer. Fabricated via a straightforward one-pot copolymerization process that includes betaine sulfonate methacrylate (SBMA) and acrylamide (AM), the hydrogel demonstrates multifunctional properties. The innovation of this hydrogel is attributed to its robust mechanical attributes, outstanding strain responsiveness, effective water retention, and advanced self-regenerative and healing capabilities, which collectively lead to its superior performance in various applications. Moreover, this hydrogel  exhibited broad-spectrum antibacterial activity. Its potential for biomechanical monitoring, especially in tandem with contact and noncontact electrocardiogram (ECG) devices, represents a noteworthy advancement in precise real-time cardiac monitoring in clinical environments. In addition, the conductive properties of the hydrogel make it an ideal substrate for electrophoretic patches aimed at treating infected wounds and consequently enhancing the healing process.

Superabsorbent carboxymethyl cellulose-based hydrogel fabricated by liquid-metal-induced double crosslinking polymerisation

Herein, we introduced a liquid-metal/polymerisable deep eutectic solvent (LM/PDES) system to the carboxymethyl cellulose (CMC) and acrylic acid solution to prepare a double-cross-linked CMC-polyacrylic acid (PAA)-LM/PDES superabsorbent hydrogel via graft crosslinking polymerisation for 5 min. FTIR and XRD provided evidence for the coordinate crosslinking between Ga3+ and carboxy groups in the CMC-PAA-LM/PDES gel structure and chemical crosslinking between CMC and PAA components. The pore size of the obtained hydrogels gradually decreases with the increase of LM-AA/PDES content. The rigid CMC polysaccharide chains increased the distance between the ionic groups on the flexible PAA molecular chains, resulting in high osmotic pressure. In addition, the synergistic effects of hydrophilic groups, electrostatic repulsion, macroporous structures and double crosslinking on the CMC and PAA structures provided a driving force and space for the gel to absorb electrolyte containing liquid. The absorption capacity of the CMC-PAA-LM/PDES gel for physiological saline reached 97 g/g, which exceeded that of a single cross-linked CMC-PAA gel and a reported superabsorbent material (71 g/g). This work solved the problem of long heating times and insufficient mechanical properties for the preparation of superabsorbent gels, providing a theoretical reference for improving the absorption capacity of superabsorbent materials for electrolyte-containing aqueous solutions.

Recent Advances in Wearable Healthcare Devices: From Material to Application

In recent years, the proliferation of wearable healthcare devices has marked a revolutionary shift in the personal health monitoring and management paradigm. These devices, ranging from fitness trackers to advanced biosensors, have not only made healthcare more accessible, but have also transformed the way individuals engage with their health data. By continuously monitoring health signs, from physical-based to biochemical-based such as heart rate and blood glucose levels, wearable technology offers insights into human health, enabling a proactive rather than a reactive approach to healthcare. This shift towards personalized health monitoring empowers individuals with the knowledge and tools to make informed decisions about their lifestyle and medical care, potentially leading to the earlier detection of health issues and more tailored treatment plans. This review presents the fabrication methods of flexible wearable healthcare devices and their applications in medical care. The potential challenges and future prospectives are also discussed.