Chestnut-Tannin-Crosslinked, Antibacterial, Antifreezing, Conductive Organohydrogel as a Strain Sensor for Motion Monitoring, Flexible Keyboards, and Velocity Monitoring

Flexible sensing devices (FSDs) fabricated using conductive hydrogels have attracted researchers’ extensive enthusiasm in recent years due to their versatility. Considering the complexity of their application environments, the integration of various functional characteristics (e.g., excellent mechanical, antibacterial, and antifreezing properties) is an important guarantee for FSDs to stably perform their applications in different environments. Herein, we developed a multifunctional conductive polyvinyl alcohol (PVA) organohydrogel PVA-CT-Ag-Al-Gly (PCAAG) by using a green, natural, and cheap biomass, chestnut tannin (CT), as a crosslinking agent, nano-silver particles (AgNPs) as an antimicrobial agent, aluminum trichloride (AlCl3) as a conducting medium, and the mixed water–glycerol as the solvent system. In this organohydrogel system, CT acted not only as the reducing and stabilizing agent for the preparation of antibacterial AgNPs but also as the crosslinking agent owing to its strong multiple hydrogen bonding interactions with PVA, realizing its multifunctional application. The PCAAG organohydrogel possessed outstanding physical and mechanical properties (350.54% of the maximum fracture strain and 1.55 MPa of the maximum tensile strength), considerable bacteriostatic effects against both Escherichia coli and Staphylococcus aureus, and excellent freeze resistance (it could function normally at −20 °C). The motion-monitoring sensor based on the PCAAG organohydrogel exhibited excellent specificity recognition for both large-amplitude (e.g., elbow bending, wrist bending, finger bending, running and walking, etc.) and small-amplitude (frowning and swallowing) human movements. The flexible keyboard constructed by using the PCAAG organohydrogel could easily achieve the transformation between digital signals and electrical signals, and the signal output had both specificity and stability. The velocity-monitoring sensor fabricated by using the PCAAG organohydrogel could accurately measure the speed of the object movement (less than 3% of relative error). In short, the present PCAAG organohydrogel solves the problems of the single application environment and a few application scenarios of traditional conductive hydrogels and possesses remarkable application potential as a multifunctional FSD in many fields such as artificial intelligence, sport management, soft robots, and human–computer interface

Wattle-Bark-Tannin-Derived Carbon Quantum Dots as Multi-Functional Nanomaterials for Intelligent Detection of Cr⁶⁺ Ions, Bio-Imaging, and Fluorescent Ink Applications

Using natural wattle bark tannin, a kind of stable, nontoxic, fluorescent carbon quantum dots (CQDs) was hydrothermally fabricated and applied as a multifunctional fluorescent nanomaterial for the determination of heavy metal ions (Cr6+ and Co2+), bio-imaging, and fluorescent ink applications. The CQDs could be assembled with polyvinyl alcohol (PVA) through hydrogen bonding to yield a composite fluorescent hydrogel that can be integrated with a smartphone to constitute a novel and convenient intelligent detection system for the rapid (10 s) real-time monitoring of Cr6+. Both the CQDs (with 1.37 μM of LOD (limit of detection)) and CQDs-PVA hydrogel (with 3.36 mg/L of LOD) sensing systems produced fast, sensitive, and selective response to Cr6+ based on the internal filtering effect and electron-transfer effect. The practicability of the CQDs-PVA fluorescence sensor was demonstrated by determining tap water and tanning wastewater samples. Based on their satisfactory fluorescence stability and solubility, the CQDs were further used for HeLa-cell imaging and as fluorescent ink for information encryption. When HeLa cells were incubated for 24 h in CQDs at a high concentration of 200 mg/L, the cell survival remained as high as 90%, and a clear fluorescence image was observed under a laser confocal fluorescence microscope. The CQD solution could be written directly as fluorescent ink on TLC (thin layer chromatography) paper, and the handwritings were invisible after drying, confirming their application potential in the field of information encryption. In summary, the present CQDs derived from wattle bark tannin exhibited excellent stability, sensitivity, and specificity in heavy metal ion sensing and also had great potential in bio-imaging and information encryption applications

CQDs-Cross-Linked Conductive Collagen/PAA-Based Nanocomposite Organohydrogel Coupling Flexibility with Multifunctionality for Dual-Modal Sensing of Human Motions

Conductive hydrogels are ideal materials for intelligent medical devices, human-machine interfaces, and flexible bioelectrodes due to their adjustable mechanical properties and electrical responsiveness, whereas it is still a great challenge to achieve the integration of excellent flexibility and biocompatibility into one hydrogel sensor while also incorporating self-healing, self-adhesion, environmental tolerance, and antimicrobial properties. Here, a nanocomposite conductive organohydrogel was constructed by using collagen (Col), alginate-derived carbon quantum dots (OSA-CQDs), poly(acrylic acid) (PAA), ethylene glycol reduced AgNPs, and Fe3+ ions. Depending on OSA-CQDs with multiple chemical binding sites and high specific surface area as cross-linkers, while coupling highly biologically active Col chains and PAA chains are serving as an energy dissipation module, the resulting organohydrogel exhibited excellent flexibility (795% of strain, 193 kPa of strength), high cell compatibility (>95% survival rate), self-healing efficiency (HE = 79.5%), antifreezing (−20 °C), moisturizing (>120 h), repeatable adhesion (strength >20 kPa, times >10), inhibitory activity against Escherichia coli and Staphylococcus aureus (9 and 21.5 cm2), conductivity, and strain sensitivity (σ = 1.34 S/m, gauge factor (GF) = 11.63). Based on the all-in-one integration of multifunction, the organohydrogel can collaboratively adapt to the multimode of strain sensing and electrophysiological sensing to realize wireless real-time monitoring of human activities and physiological health. Therefore, this work provides a new and common platform for the design and sensing of next-generation hydrogel-based smart wearable sensors

Cleaner, High-Efficiency, and High-Value Conversion of Chrome-Containing Leather Solid Waste into Carbon Quantum Dots as Renewable Bimetallic Ions Detection Sensors

A simple hydrothermal method was conducted to transform chrome shavings (CS) into carbon quantum dots (CS-CQDs) that were then applied as supersensitive chemical sensors for the detection of Cr6+ (1.40 μM limit of detection (LOD)) and Fe3+ (1.67 μM LOD) ions. Meanwhile, most of the chromium in CS deposited in the resulting precipitate, realizing the separation and recovery of chromium. CS-CQDs were further used to prepare an “intelligent fluorescent switchable sensor” (IFSS) hydrogel with high sensitivity for the identification of Cr6+ in tannery wastewater (LOD of 45.59 μmol/L). Interestingly, the quenched IFSS-Cr6+ hydrogel system could be applied to determine ascorbic acid (AA) with a LOD of 21.33 μmol/L, owing to the reduction of Cr6+ into Cr3+ by AA and thus the IFSS’s fluorescence regeneration. This ″fluorescent on/off″ effect could be recycled at least four times. IFSS hydrogel also could adsorb Cr6+ ions (13.50 mg/g) and is done so after the reduction by AA. The possible sensing mechanism to Cr6+ was confirmed to be the internal filtration effect and electron transfer. This work not only developed a feasible and clean recycling method of CS but also produced a smart functional material for the determination and separation of Cr6+, achieving “turning trash into treasure”

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

Living ROMP Syntheses and Redox Properties of Triblock Metallocopolymer Redox Cascades

A number of reports have described the synthesis by ring-opening metathesis polymerization (ROMP) of diblock metallopolymers containing ferrocene and organocobalt complexes using the very efficient Grubb’s third-generation metathesis catalyst. Here the first triblock metallocopolymers are reported using this catalyst with ferrocenyl, pentamethyl­ferrocenyl, and cobalticenyl groups in the side chains of a polynorbornene backbone. Among the six possible synthetic schemes for the successive ROMP reactions of the blocks, two of them have been successfully conducted with adequate characterization using the end-group analysis, MALDI-TOF mass spectroscopy, and Bard–Anson’s electrochemical method. The cyclic voltammetry studies showed that the integrity of reversible redox systems was preserved in cascades of heterogeneous electron transfers in both metallocopolymers with significant adsorption and electrostatic effects. This research paves the way for the design and synthesis of multiblock metallocopolymers offering access to multiproperty nanomaterials

Tara Tannin-Cross-Linked, Underwater-Adhesive, Super Self-Healing, and Recyclable Gelatin-Based Conductive Hydrogel as a Strain Sensor

Conductive hydrogel strain sensors have triggered extensive research interest in artificial intelligence, human motion detection, electronic skin, and other technical fields. However, it is still challenging work to prepare conductive hydrogels integrated with good biocompatibility, recyclability, self-healing, and strong adhesion properties both in air and underwater. Herein, a novel, ultraexcellent self-healing, adhesive, and multifunctional gelatin composite hydrogel was fabricated through a simple and rapid one-pot method in which gelatin (Gel) and polyvinyl alcohol (PVA) were used as the polymeric skeletons, Tara tannin as the cross-linking agent, and multiwalled carbon nanotubes (CNTs) as the conducting medium. Inspired by the vegetable tanning mechanism in tanning chemistry, the multiple hydrogen bonding and hydrophobic interactions of Tara tannin with Gel were used to build the cross-linking network of the hydrogel. The obtained GTPC (Gel-Tara tannin-PVA-CNTs) hydrogel exhibited considerable stretchability (760%), strong adhesion strength (16 kPa to pigskin), and high conductive sensitivity (gauge factor (GF) = 6.79). In particular, the GTPC hydrogel displayed good repeatable adhesion (≥10 times) and rapid self-healing performance (HE (self-healing efficiency) > 99%) both in air and underwater. The formed GTPC hydrogel strain sensor could accurately detect various motion signals, such as finger bending, ankle bending, and smiling, and it could also sensitively capture sensing signals of body movements underwater. The self-healed hydrogel sensor also exhibited a similar motion sensing ability to the original one. This work affords a new idea and method for the design and fabrication of flexible strain sensors with rapid air and underwater self-healing performance, high sensitivity, and strong adhesion (in air and water) by using vegetable tannin, promoting the underwater application of sensors and the diversified utilization of vegetable tannin

Tara Tannin-Cross-Linked, Underwater-Adhesive, Super Self-Healing, and Recyclable Gelatin-Based Conductive Hydrogel as a Strain Sensor

Conductive hydrogel strain sensors have triggered extensive research interest in artificial intelligence, human motion detection, electronic skin, and other technical fields. However, it is still challenging work to prepare conductive hydrogels integrated with good biocompatibility, recyclability, self-healing, and strong adhesion properties both in air and underwater. Herein, a novel, ultraexcellent self-healing, adhesive, and multifunctional gelatin composite hydrogel was fabricated through a simple and rapid one-pot method in which gelatin (Gel) and polyvinyl alcohol (PVA) were used as the polymeric skeletons, Tara tannin as the cross-linking agent, and multiwalled carbon nanotubes (CNTs) as the conducting medium. Inspired by the vegetable tanning mechanism in tanning chemistry, the multiple hydrogen bonding and hydrophobic interactions of Tara tannin with Gel were used to build the cross-linking network of the hydrogel. The obtained GTPC (Gel-Tara tannin-PVA-CNTs) hydrogel exhibited considerable stretchability (760%), strong adhesion strength (16 kPa to pigskin), and high conductive sensitivity (gauge factor (GF) = 6.79). In particular, the GTPC hydrogel displayed good repeatable adhesion (≥10 times) and rapid self-healing performance (HE (self-healing efficiency) > 99%) both in air and underwater. The formed GTPC hydrogel strain sensor could accurately detect various motion signals, such as finger bending, ankle bending, and smiling, and it could also sensitively capture sensing signals of body movements underwater. The self-healed hydrogel sensor also exhibited a similar motion sensing ability to the original one. This work affords a new idea and method for the design and fabrication of flexible strain sensors with rapid air and underwater self-healing performance, high sensitivity, and strong adhesion (in air and water) by using vegetable tannin, promoting the underwater application of sensors and the diversified utilization of vegetable tannin

Tara Tannin-Cross-Linked, Underwater-Adhesive, Super Self-Healing, and Recyclable Gelatin-Based Conductive Hydrogel as a Strain Sensor

Conductive hydrogel strain sensors have triggered extensive research interest in artificial intelligence, human motion detection, electronic skin, and other technical fields. However, it is still challenging work to prepare conductive hydrogels integrated with good biocompatibility, recyclability, self-healing, and strong adhesion properties both in air and underwater. Herein, a novel, ultraexcellent self-healing, adhesive, and multifunctional gelatin composite hydrogel was fabricated through a simple and rapid one-pot method in which gelatin (Gel) and polyvinyl alcohol (PVA) were used as the polymeric skeletons, Tara tannin as the cross-linking agent, and multiwalled carbon nanotubes (CNTs) as the conducting medium. Inspired by the vegetable tanning mechanism in tanning chemistry, the multiple hydrogen bonding and hydrophobic interactions of Tara tannin with Gel were used to build the cross-linking network of the hydrogel. The obtained GTPC (Gel-Tara tannin-PVA-CNTs) hydrogel exhibited considerable stretchability (760%), strong adhesion strength (16 kPa to pigskin), and high conductive sensitivity (gauge factor (GF) = 6.79). In particular, the GTPC hydrogel displayed good repeatable adhesion (≥10 times) and rapid self-healing performance (HE (self-healing efficiency) > 99%) both in air and underwater. The formed GTPC hydrogel strain sensor could accurately detect various motion signals, such as finger bending, ankle bending, and smiling, and it could also sensitively capture sensing signals of body movements underwater. The self-healed hydrogel sensor also exhibited a similar motion sensing ability to the original one. This work affords a new idea and method for the design and fabrication of flexible strain sensors with rapid air and underwater self-healing performance, high sensitivity, and strong adhesion (in air and water) by using vegetable tannin, promoting the underwater application of sensors and the diversified utilization of vegetable tannin

Tara Tannin-Cross-Linked, Underwater-Adhesive, Super Self-Healing, and Recyclable Gelatin-Based Conductive Hydrogel as a Strain Sensor

Conductive hydrogel strain sensors have triggered extensive research interest in artificial intelligence, human motion detection, electronic skin, and other technical fields. However, it is still challenging work to prepare conductive hydrogels integrated with good biocompatibility, recyclability, self-healing, and strong adhesion properties both in air and underwater. Herein, a novel, ultraexcellent self-healing, adhesive, and multifunctional gelatin composite hydrogel was fabricated through a simple and rapid one-pot method in which gelatin (Gel) and polyvinyl alcohol (PVA) were used as the polymeric skeletons, Tara tannin as the cross-linking agent, and multiwalled carbon nanotubes (CNTs) as the conducting medium. Inspired by the vegetable tanning mechanism in tanning chemistry, the multiple hydrogen bonding and hydrophobic interactions of Tara tannin with Gel were used to build the cross-linking network of the hydrogel. The obtained GTPC (Gel-Tara tannin-PVA-CNTs) hydrogel exhibited considerable stretchability (760%), strong adhesion strength (16 kPa to pigskin), and high conductive sensitivity (gauge factor (GF) = 6.79). In particular, the GTPC hydrogel displayed good repeatable adhesion (≥10 times) and rapid self-healing performance (HE (self-healing efficiency) > 99%) both in air and underwater. The formed GTPC hydrogel strain sensor could accurately detect various motion signals, such as finger bending, ankle bending, and smiling, and it could also sensitively capture sensing signals of body movements underwater. The self-healed hydrogel sensor also exhibited a similar motion sensing ability to the original one. This work affords a new idea and method for the design and fabrication of flexible strain sensors with rapid air and underwater self-healing performance, high sensitivity, and strong adhesion (in air and water) by using vegetable tannin, promoting the underwater application of sensors and the diversified utilization of vegetable tannin