Tough, Self-Adhesive, Antibacterial, and Recyclable Supramolecular Double Network Flexible Hydrogel Sensor Based on PVA/Chitosan/Cyclodextrin

Hydrogel-based flexible sensors have attracted extensive attention of researchers due to their great application potential in soft robots, electronic skin, motion monitoring, and disease diagnosis. However, it is still a challenge for hydrogel-based flexible sensors to be integrated with good mechanical performance, sensitivity, self-adhesion, fatigue resistance, antibacterial activity, and recyclability. Here, a novel supramolecular polyoxymethylene cross-linking agent (PCD-Fc-CHO) was designed and synthesized by the host–guest interaction between poly­(β-cyclodextrin) and ferrocene. Then, a double network (DN) hydrogel was prepared by a PVA crystallization domain via the freeze-thaw cycle method (first network) and Schiff base between PCD-Fc-CHO and chitosan (second network). The obtained DN hydrogel was immersed in the NaCl solution to form a conductive DN hydrogel. The resulting hydrogel has excellent mechanical properties [tensile (314%, 0.5 MPa), compress (50%, 0.663 MPa)], good fatigue resistance (stretching and compressing cycles at least five times), reliable conductivity (2.48 S/m), high sensitivity [gauge factor (GF) = 4.87], antibacterial, and recyclable properties. In addition, an industrially produced and low-cost plant polyphenol, black wattle tannin, was used for the first time to give the hydrogel good adhesion and repeated adhesion (at least ten times). The obtained hydrogel can be used as a flexible strain sensor to monitor both large movements (bending finger, wrist, elbow, arm, and knee) and micromovements (talking, smiling, blinking, blowing, frowning, and drinking) with high sensitivity and stability. It is noteworthy that the reshaped hydrogel also exhibits sensitive sensing performance, indicating that the hydrogel can be recycled. This work expanded the strategy for the design and preparation of multi-functional DN hydrogels and promoted the application of wearable, highly sensitive, fatigue resistance, antibacterial, and green hydrogel sensors

Collagen-Based Organohydrogel Strain Sensor with Self-Healing and Adhesive Properties for Detecting Human Motion

Conductive hydrogels are ideal for flexible sensors, but it is still a challenge to produce such hydrogels with combined toughness, self-adhesion, self-healing, anti-freezing, moisturizing, and biocompatibility properties. Herein, inspired by natural skin, a highly stretchable, strain-sensitive, and multi-environmental stable collagen-based conductive organohydrogel was constructed by using collagen (Col), acrylic acid, dialdehyde carboxymethyl cellulose, 1,3-propylene glycol, and AlCl3. The resulting organohydrogel exhibited excellent tensile (strain >800%), repeatable adhesion (>10 times), self-healing [self-healing efficiency (SHE) ≈ 100%], anti-freezing (−60 °C), moisturizing (>20 d), and biocompatible properties. This organohydrogel also possessed good electrical conductivity (σ = 3.4 S/m) and strain-sensitive properties [GF (gauge factor) = 13.65 with the maximal strain of 400%]. Notably, the organohydrogel had a considerable low-temperature self-healing performance (SHE = 88% at −24 °C) and rapid underwater self-healing property (SHE = 92%, self-healing time <20 min). This type of strain sensor could not only accurately and continuously monitor the large-scale motions of the human body but also provide an accurate response to the human tiny motions. This work not only proposes a development strategy for a multifunctional conductive organohydrogel with multiple environmental stability but also provides potential research value for the construction of biomimetic electronic skin

Collagen-Based Organohydrogel Strain Sensor with Self-Healing and Adhesive Properties for Detecting Human Motion

Conductive hydrogels are ideal for flexible sensors, but it is still a challenge to produce such hydrogels with combined toughness, self-adhesion, self-healing, anti-freezing, moisturizing, and biocompatibility properties. Herein, inspired by natural skin, a highly stretchable, strain-sensitive, and multi-environmental stable collagen-based conductive organohydrogel was constructed by using collagen (Col), acrylic acid, dialdehyde carboxymethyl cellulose, 1,3-propylene glycol, and AlCl3. The resulting organohydrogel exhibited excellent tensile (strain >800%), repeatable adhesion (>10 times), self-healing [self-healing efficiency (SHE) ≈ 100%], anti-freezing (−60 °C), moisturizing (>20 d), and biocompatible properties. This organohydrogel also possessed good electrical conductivity (σ = 3.4 S/m) and strain-sensitive properties [GF (gauge factor) = 13.65 with the maximal strain of 400%]. Notably, the organohydrogel had a considerable low-temperature self-healing performance (SHE = 88% at −24 °C) and rapid underwater self-healing property (SHE = 92%, self-healing time <20 min). This type of strain sensor could not only accurately and continuously monitor the large-scale motions of the human body but also provide an accurate response to the human tiny motions. This work not only proposes a development strategy for a multifunctional conductive organohydrogel with multiple environmental stability but also provides potential research value for the construction of biomimetic electronic skin

Highly Sensitive and Robust Polysaccharide-Based Composite Hydrogel Sensor Integrated with Underwater Repeatable Self-Adhesion and Rapid Self-Healing for Human Motion Detection

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly­(acrylic acid) (PAA), and aluminum ions (Al3+). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments

Multifunctional Ionic Conductive Double-Network Hydrogel as a Long-Term Flexible Strain Sensor

Hydrogel-based sensors have attracted a lot of attention owing to their promising applications in human–machine interfaces, personal health monitoring, and soft robotics. However, there is still a great challenge in the fabrication of conductive hydrogel sensors with good mechanical strength, self-healing property, transparency, self-adhesiveness, antibacterial performance, high conductivity, and sensitivity. To meet these requirements, a multifunctional ionic conductive double-network (DN) hydrogel was prepared via in situ free-radical polymerization using a simple one-pot method based on AlCl3, acrylic acid, oxide sodium alginate, and aminated gelatin. The hydrogel network was constructed via metal coordination and Schiff base. The resultant DN hydrogel showed self-healing behavior in an ambient environment and underwater with high healing efficiency. Notably, the water environment can effectually accelerate the self-healing process of the hydrogel. Moreover, the corresponding hydrogel displayed good self-adhesiveness, transparency (over 90%), stretchability, antibacterial ability, and high conductivity and sensitivity. This hydrogel was further utilized as a sensor to monitor various human movements and object deformations in daily life. Significantly, the hydrogel that was placed in a closed environment for 10 days still possessed those performances mentioned above. Additionally, the healed hydrogel also maintained the sensing behavior. This work may enlighten future research to design fully functional hydrogel-based sensors to adapt to the environment

Tough, Repeatedly Adhesive, Cyclic Compression-Stable, and Conductive Dual-Network Hydrogel Sensors for Human Health Monitoring

Hydrogel-based flexible wearable devices have attracted wide attention from researchers due to their great potential application in human–computer interaction, electronic skin, and disease diagnosis. However, the preparation of conductive hydrogels integrating good biocompatibility, excellent mechanical (tensile and compressible) properties, self-adhesive properties, cyclic stretching, and compression stability remains a challenge. By the Schiff base reaction between dialdehyde carboxymethyl cellulose and amino gelatin to form the first layer of the network and by the free-radical polymerization of acrylic acid to form the second layer of the network, a multifunctional conductive dual-network (DN) hydrogel strain sensor was prepared. The composite DN hydrogel has excellent compression properties (the strength reached to 0.12 MPa when the hydrogel was compressed to 50% of its original height), good cyclic compression (≥10 000 times), repeatable adhesion (≥10 times), reliable electrical conductivity, and high sensitivity (gauge factor = 8.1). The biocompatible hydrogel can be used not only to monitor human body movement but also to detect the breathing movement of simulated pig lungs in vitro. Furthermore, the conductive hydrogel was creatively made into a plantar pressure sensor similar to an insole to monitor the stress on the sole of a flatfoot patient, providing a new potential material for flatfoot detection and correction

Highly Sensitive and Robust Polysaccharide-Based Composite Hydrogel Sensor Integrated with Underwater Repeatable Self-Adhesion and Rapid Self-Healing for Human Motion Detection

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly­(acrylic acid) (PAA), and aluminum ions (Al3+). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments

Multifunctional Ionic Conductive Double-Network Hydrogel as a Long-Term Flexible Strain Sensor

Hydrogel-based sensors have attracted a lot of attention owing to their promising applications in human–machine interfaces, personal health monitoring, and soft robotics. However, there is still a great challenge in the fabrication of conductive hydrogel sensors with good mechanical strength, self-healing property, transparency, self-adhesiveness, antibacterial performance, high conductivity, and sensitivity. To meet these requirements, a multifunctional ionic conductive double-network (DN) hydrogel was prepared via in situ free-radical polymerization using a simple one-pot method based on AlCl3, acrylic acid, oxide sodium alginate, and aminated gelatin. The hydrogel network was constructed via metal coordination and Schiff base. The resultant DN hydrogel showed self-healing behavior in an ambient environment and underwater with high healing efficiency. Notably, the water environment can effectually accelerate the self-healing process of the hydrogel. Moreover, the corresponding hydrogel displayed good self-adhesiveness, transparency (over 90%), stretchability, antibacterial ability, and high conductivity and sensitivity. This hydrogel was further utilized as a sensor to monitor various human movements and object deformations in daily life. Significantly, the hydrogel that was placed in a closed environment for 10 days still possessed those performances mentioned above. Additionally, the healed hydrogel also maintained the sensing behavior. This work may enlighten future research to design fully functional hydrogel-based sensors to adapt to the environment

Highly Sensitive and Robust Polysaccharide-Based Composite Hydrogel Sensor Integrated with Underwater Repeatable Self-Adhesion and Rapid Self-Healing for Human Motion Detection

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly­(acrylic acid) (PAA), and aluminum ions (Al3+). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments

Highly Sensitive and Robust Polysaccharide-Based Composite Hydrogel Sensor Integrated with Underwater Repeatable Self-Adhesion and Rapid Self-Healing for Human Motion Detection

Tough, biocompatible, and conductive hydrogel-based strain sensors are attractive in the fields of human motion detection and wearable electronics, whereas it is still a great challenge to simultaneously integrate underwater adhesion and self-healing properties into one hydrogel sensor. Here, a highly stretchable, sensitive, and multifunctional polysaccharide-based dual-network hydrogel sensor was constructed using dialdehyde carboxymethyl cellulose (DCMC), chitosan (CS), poly­(acrylic acid) (PAA), and aluminum ions (Al3+). The obtained DCMC/CS/PAA (DCP) composite hydrogels exhibit robust mechanical strength and good adhesive and self-healing properties, due to the reversible dynamic chemical bonds and physical interactions such as Schiff base bonds and metal coordination. The conductivity of hydrogel is 2.6 S/m, and the sensitivity (gauge factor (GF)) is up to 15.56. Notably, the DCP hydrogel shows excellent underwater repeatable adhesion to animal tissues and good self-healing properties in water (self-healing rate > 90%, self-healing time < 10 min). The DCP hydrogel strain sensor can sensitively monitor human motion including finger bending, smiling, and wrist pulse, and it can steadily detect human movement underwater. This work is expected to provide a new strategy for the design of high-performance intelligent sensors, particularly for applications in wet and underwater environments