The demand for interfacing electronics in everyday life is rapidly accelerating, with an ever-growing number of applications in wearable electronics and electronic skins for robotics, prosthetics, and other purposes. Soft sensors that efficiently detect environmental or biological/physiological stimuli have been extensively studied due to their essential role in creating the necessary interfaces for these applications. Unfortunately, due to their natural softness, these sensors are highly sensitive to structural and mechanical damage. The integration of natural properties, such as self-healing, into these systems should improve their reliability, stability, and long-term performance. Recent studies on self-healing soft sensors for varying chemical and physical parameters are herein reviewed. In addition, contemporary studies on material design, device structure, and fabrication methods for sensing platforms are also discussed. Finally, the main challenges and future perspectives in this field are introduced, while focusing on the most promising examples and directions already reported.

Self-Healing Soft Sensors: From Material Design to Implementation.

Flexible and conductive hydrogel sensors have great potential for applications in wearable and implantable devices, electronic skin and healthcare diagnosis. However, it remains a great challenge to develop an integrated tough hydrogel sensor combining stretchability, adhesiveness, self-healing ability and high sensitivity via a simple, fast and economical approach for multi-field applications. In this work, we designed a multifunctional composite self-adhesive conductive hydrogel by using chitosan (CS), tannic acid (TA) and polyacrylic acid (PAA), and ionic cross-linker Al3+. The synergistic multiple and reversible coordination bonds and hydrogen bonds in the matrix lead to a combination of high stretchability, rapid self-recovery, great anti-fatigue and rapid self-healing properties of the tough hydrogel. Additionally, the ionic gels displayed durable and repeatable adhesiveness ascribed to the presence of catechol groups from TA, which can adhere directly on human skin without residuals and inflammatory responses. Furthermore, our ionic hydrogel sensors exhibited a broad strain window (0–1400%) and demonstrated brilliant stretching sensitivity (gauge factor as high as 12.2), and it displayed stable sensing performance for repeated real-time monitoring of both large and subtle deformation (e.g. knee joint motions, breathing modes, and even the slight pulse changes in different motion states). This work provides a feasible method to construct self-adhesive and self-healing hydrogel sensors with high sensitivity and a large-range detection capacity and paves a way for versatile applications in electronic skin, healthcare monitoring and medical electrodes.

A self-adhesive wearable strain sensor based on a highly stretchable, tough, self-healing and ultra-sensitive ionic hydrogel

In addition to conductivity, recent evidence suggests that adhesive, self-healing, and antibacterial properties are also important aspects of wearable force sensors. However, preparation of hydroge...

Adhesive, Conductive, Self-Healing, and Antibacterial Hydrogel Based on Chitosan–Polyoxometalate Complexes for Wearable Strain Sensor

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

A review on recent advances in gel adhesion and their potential applications

Development of hydrogels possessing toughness, extensibility, resilience, and self-healability together is challenging. Herein, we demonstrate that incorporation of polyacryloyl hydrazide (PAHz) substantially improves the mechanical properties and incorporates self-healing, adhesive and strain sensing properties in ionic hydrogels. For example, the compressive strength (80 MPa), tensile strength (0.7 MPa) and fracture energy (∼902 J m−2) values of polyacrylamido-2-methylpropanesulfonic acid (PAMPS)-based hydrogels prepared by adding ∼6.5 wt% of PAHz increased by 73, 18 and 451 times, respectively, compared to that of the control. The presence of PAHz in the PAMPS hydrogel matrix provided additional physical crosslinking in the form of SO3−⋯H3N+–ionic interaction and created network reinforced zones that dissipated energy under stress and improved the toughness of the hydrogel system. At low water content (≤10 wt%), the compressive strength further increased to an unprecedented value of 0.4 GPa while maintaining adequate compressibility (92%). The PAHz incorporated-hydrogels exhibit an impressive adhesive strength value of up to 2.8 MPa on glass substrates, quick autonomous self-healing ability and strain sensing properties with a gauge factor value of up to 0.7. This general one-pot strategy may be extended to other ionic hydrogel systems for the improvement of mechanical properties.

Polyacryloyl hydrazide incorporation into ionic hydrogels improves toughness, elasticity, self-healability, adhesive & strain sensing properties

Mycobacterium tuberculosis (M.tb.) enoyl-acyl carrier protein (ACP) reductase (InhA) is validated as a useful target for tuberculosis therapy and is considered an attractive enzyme to drug discovery. This study aimed to identify the novel inhibitor of the InhA enzyme, a potential target of M.tb. involved in the type II fatty acid biosynthesis pathway that controls mycobacterial cell envelope synthesis. We compiled 80 active compounds from Ruta graveolens and citrus plants belonging to the Rutaceae family for pharmacokinetics and molecular docking analyses. The chemical structures of the 80 phytochemicals and the 3D structure of the target protein were retrieved from the PubChem database and RCSB Protein Data Bank, respectively. The evaluation of druglikeness was performed based on Lipinski’s Rule of Five, while the computed phytochemical properties and molecular descriptors were used to predict the ADMET of the compounds. Amongst these, 11 pharmacokinetically-screened compounds were further examined by performing molecular docking analysis with an InhA target using AutoDock 4.2. The docking results showed that gravacridonediol, a major glycosylated natural alkaloid from Ruta graveolens, might possess a promising inhibitory potential against InhA, with a binding energy (B.E.) of −10.80 kcal/mole and inhibition constant (Ki) of 600.24 nM. These contrast those of the known inhibitor triclosan, which has a B.E. of −6.69 kcal/mole and Ki of 12.43 µM. The binding efficiency of gravacridonediol was higher than that of the well-known inhibitor triclosan against the InhA target. The present study shows that the identified natural compound gravacridonediol possesses drug-like properties and also holds promise in inhibiting InhA, a key target enzyme of M.tb.

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Identification of Novel Inhibitor of Enoyl-Acyl Carrier Protein Reductase (InhA) Enzyme in Mycobacterium tuberculosis from Plant-Derived Metabolites: An In Silico Study

Bio-based polydimethylsiloxane porous sponge materials with programmable hydrophobicity and porosity for efficient separation of hydrophobic liquids from water

Niharika Pandey

Papers

Polyacryloyl hydrazide incorporation into ionic hydrogels improves toughness, elasticity, self-healability, adhesive & strain sensing properties

Identification of Novel Inhibitor of Enoyl-Acyl Carrier Protein Reductase (InhA) Enzyme in Mycobacterium tuberculosis from Plant-Derived Metabolites: An In Silico Study

Bio-based polydimethylsiloxane porous sponge materials with programmable hydrophobicity and porosity for efficient separation of hydrophobic liquids from water