Lignin based hydrogels in strain sensor applications.
| Hydrogel composition | Lignin kind | Synthesis | Properties | Applications | References |
|---|---|---|---|---|---|
| Polyvinyl alcohol (PVA), carboxymethyl chitosan (CMC), cellulose nanofibrils (CNF), lignin-based carbon (LC) nanoparticles | Lignin-derived carbon (LC) | Dispersed lignin-based carbon (LC) was combined with PVA, CMC, and CNF that had been dissolved in water. Several freeze-thaw cycles were used to the mixture in order to create a physically crosslinked conductive hydrogel (PSH) | Tensile strength: 133 kPa, compression stress: 37.7 kPa, excellent stretchability and fatigue resistance | Monitoring palm clutching, finger bending, elbow flexion, wearable flexible strain sensors | [73] |
| Enzymatic hydrolysis lignin (DEL), poly (vinyl alcohol) (PVA), silver nanoparticles (AgNP) | Enzymatic hydrolysis lignin (DEL) | In situ reduction of Ag+ with sodium citrate in DEL-PVA matrix; promotes nanophase separation and AgNP formation | Strain at break: 1,220%, tensile strength: 13.3 MPa, toughness: 78.1 MJ/m3, electrical conductivity: ~1.0 S/m | Flexible and wearable strain sensors, motion-responsive electronic devices | [74] |
| Sulfonated lignin-coated silica nanoparticles (LSNs), polyacrylamide (PAM), ferric ions (Fe3+) | Sulfonated lignin | Rapid gelation in ~60 seconds via self-catalytic redox reaction between Fe3+ and catechol groups on LSNs | Elongation: ~1,100%, tensile strength: ~180 kPa, compressive strength: ~480 kPa, hysteresis ratio: < 15% | Strain sensors for wearable electronics, human motion tracking | [75] |
| Lignin-graft-poly(acrylic acid) (LPAA), acrylamide (AM), sodium chloride (NaCl) | Lignin-graft-poly (acrylic acid) (LPAA) | By adding LPAA to an AM/NaCl solution, composite conductive hydrogels were created, creating a hydrogen-bonded crosslinked network without the need for outside stimuli | Excellent UV shielding: 99.95%, good transparency, strain sensing: gauge factor = 2.51 (100–500% strain range), tensile strength: 96 kPa, compressive strength: 0.54 MPa | Wearable strain sensors for physical activity monitoring, flexible and transparent electronics, UV-protective wearable devices | [76] |
| Gelatin, polypyrrole, sodium lignosulfonate | Sodium lignosulfonate | Simple fabrication via dynamic noncovalent interactions | Biocompatibility, conductivity, high strain sensitivity: GF = 6.08, fast response: 107 milliseconds, strong adhesion: 23.88 kPa to pig skin | Wearable flexible strain sensors, real-time monitoring of human physiological activities | [77] |
| Lignin–Fe3+ self-catalytic system, 2-hydroxyethyl acrylate (HE-AA), [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS), water–ethylene glycol (EG) mixture | Lignin–Fe3+ | Rapid redox polymerization of lignin–Fe3+ with HE-AA and DMAPS in EG solution | Fracture stress: 236.15 kPa, elongation at break: 556.8%, self-adhesion: ~110 ± 3.1 kPa on paper, water retention: 73.7% (non-drying), antifreezing: stable from −60°C to 60°C, sensor performance-gauge factor: 6.044, response time: 198 ms | Strain sensors for skin-mounted flexible electronics, wearable health monitoring and motion tracking | [78] |
| Poly (acrylic acid) (PAA), liquid metal (LM), TEMPO-oxidized lignin | TEMPO-oxidized lignin | The hydrogel was created by polymerizing acrylic acid with free radicals at room temperature. TEMPO-oxidized lignin was used to stabilize the liquid metal and start the gel formation process | High conductivity, self-healing, strong adhesion, high tensile strength, antibacterial activity (due to lignin), strain sensing accuracy, stable electrical output | Flexible and wearable sensors, electronic skin (e-skin), health monitoring devices, soft robotics | [79] |
| Lignosulfonate (LS), ferric ions (Fe), nanocellulose | Lignosulfonate (LS) | By combining lignosulfonate, Fe2+ ions, and nanocellulose, the hydrogel was quickly created at ambient temperature in 63 seconds without the requirement for UV light or additional heating | Rapid gelation (as fast as 63 seconds with 8 wt% LS), high tensile strength: 227 kPa, excellent elongation at break: 515%, self-supporting and flexible structure | Wearable strain sensors for monitoring human joint movement, flexible electronics, potential for biomedical and motion detection devices | [80] |
| Sulfonated lignin–silica nanoparticles (LSNs), iron ions (Fe3+), polyacrylamide (PAM), MXene (Ti3C2Tx) | Sulfonated lignin | SNs, Fe3+, and MXene were combined at room temperature to synthesize the hydrogel. | Tensile strength: ~76 kPa, elongation at break: ~700%, self-adhesion: ~19.9 kPa | Flexible and wearable strain sensor electronics, human motion sensing and health monitoring | [81] |
HK: Conceptualization, Visualization, Data curation, Writing—review & editing, Writing—original draft. Disha: Data curation, Writing—review & editing. KS: Data curation, Writing—review & editing. OS: Project administration, Supervision, Writing—review & editing. BS: Conceptualization, Investigation, Project administration, Supervision, Writing—review & editing. All authors read and approved the submitted version.
The authors declare that they have no conflicts of interest.
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The authors would like to thank the Department of Pharmaceutical Sciences and Drug Research, Punjabi University, Patiala and Bioinformatics center (BIC) sponsored by Department of Biotechnology for providing a computational facility under the BIC (Bt/PR39876/Btis/137/7/2021), New Delhi, India. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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