Mussel‐Inspired Flexible, Wearable, and Self‐Adhesive Conductive Hydrogels for Strain Sensors

Abstract

delamination of electronic conductors and substrates pose significant challenges in strain sensor applications such as detection of biological signals of human motion. [7] Furthermore, these traditional sensors are mounted on the skin by additional adhesives, mechanical clamps, or straps to achieve long-term practical application. [8] Currently, researchers have focused on identifying new promising candidate materials to overcome these defects.Hydrogels are three-dimensional (3D) polymeric networks with good stretchability, viscoelasticity, and swelling properties. [9] Due to their outstanding performance, many stretchable hydrogels have been increasingly applied to the field of wearable strain sensors. [10][11][12][13][14] For instance, Li et al. [15] developed a dual physically crosslinked polymer hydrogel with hydrogen bonding and ionic coordination. As a strain sensor, it has high sensitivity to pressure and deformation and can detect the human body movement. However, this hydrogel requires additional double-sided tape to be attached to the skin due to the lack of self-adhesion, which limits its application in wearable devices. Thus, an extended function (e.g., self-adhesive performance) is promising for motion detection and allows easy skin adhesion. Currently, the development of a hydrogel-based composite strain sensor with excellent stretchability and selfadhesive properties remains a considerable challenge. Recently, mussel-inspired adhesive hydrogels have demonstrated excellent performance and served as an inspiration for the design and fabrication of other types of self-adhesive hydrogels. Mussels can firmly adhere to all surfaces by noncovalent and covalent chemical interactions regardless of surface roughness. [16] Dopamine (DA), which has a protein-catechol group that is similar to that used in mussel adhesion, has been widely used to fabricate selfadhesive and conductive hydrogels. [17] More importantly, DA provides a new perspective for the development of wearable strain sensors with excellent self-adhesive properties. For instance, Liu et al. [18] reported a hydrogel-based self-adhesive and self-healing epidermal strain sensor by adding Polydopamine (PDA) to PVA; the developed sensor can detect minute epidermal deformations (0.1% strain) and large body movements (10-75% strain) such as throat vibration and finger bending. In addition, it can be used in the field of low-intensity strain sensing. Furthermore, Zhang et al. [19] prepared a conductive, healable, and self-adhesive hydrogel-based sensor by dynamic supramolecular cross-linkingThe latest generation of wearable devices features materials that are flexible, conductive, and stretchable, thus meeting the requirements of stability and reliability. However, the metal conductors that are currently used in various equipments cannot achieve these high performance expectations. Hence, a mussel-inspired conductive hydrogel (HAC-B-PAM) is prepared with a facile approach by employing polyacrylamide (PAM), dopamine-functionalized hyaluronic acid (HAC), ...

Flexible Self‐Repairing Materials for Wearable Sensing Applications: Elastomers and Hydrogels

“…Ion conductive hydrogels consist of a large number of free ions in a 3D polymer network with similar flexibility as biological systems, making them ideal candidates for wearable flexible devices. In recent studies of self-healing ionic conductive hydrogel flexible sensors, conductive ions such as Fe 3+ , [124,125] Na + , [126][127][128][129] [110] glycerol-plasticized polyvinyl alcohol-borax (PVA-borax) / 0.05 [111] polyvinyl alcohol, phenylboronic acid grafted alginate, and polyacrylamide 1.1 × 10 −2 0.064 [112] polyvinyl alcohol and borax / 0.23 [74] Carbon nanotubes polyacrylamide /chitosan hybrid / 0.06 [113] hydrophobic associated polyacrylamide hydrogel / 0.3 [114] Polyacrylamide hydrogels 0.5 0.91 [115] Silver nanoparticles polyion complex/polyaniline hybrid / 3. Al 3+ , [130] ammonium persulfate, [131] sulfuric acid, [132] and lithium chloride [133,134] have been reported.…”

Self‐healing Polyol/Borax Hydrogels: Fabrications, Properties and Applications

“…second network improved mechanical properties [81] PVA/P(AAm-co-SA) -second network improved mechanical and pH-responsive properties [82] PVA/AG -AG boost self-healing and improved mechanical strength [83] LBG/Gg pH-driven shape memory ultrafast self-healing with high mechanical properties [84] PVA/CST -CST improved machinal properties [85] HA-DP Corsslinked PAAm strain sensors mussel-inspired flexible, wearable, and self-adhesive [86] Other types of borax-based hydrogels oxidized-alginate gelatin injectable in situ forming biodegradable scaffolds for cartilage regeneration and/or treatment of meniscal injuries gelatin create dynamic imine crosslinking with oxidized alginate [87][88][89] PVA/PSA/PNIPAAm thermoresponsive touch sensors PSA/PNIPAAm improved mechanical properties; induce thermo-sensitivity Although the history for the synthesis of polyol/B hydrogels, such as PVA/B [33,40] and galactomannan/B [41] hydrogels, is turned back to the 20 th century, more detailed studies have been performed on the characteristics of these hydrogels in recent years. The stability evaluation of scleroglucan (Sclg)/B hydrogels in aqueous media showed that in high acidic and high alkaline media the stability is reduced significantly.…”

“…Lv et al prepared mussel-inspired flexible, wearable, and self-adhesive conductive hydrogels for strain sensors via the dual crosslinking with borax and free radical copolymerization. [86] First, dopamine (DP) was conjugated to the carboxylate groups of hyaluronic acid (HA). Subsequently, a homogenous aqueous solution of HA-DP, borax, MBA, and AAm was exposed to polymerization using APS/TEMED as initiation system at 4°C.…”

“…Lv et al prepared mussel‐inspired flexible, wearable, and self‐adhesive conductive hydrogels for strain sensors via the dual crosslinking with borax and free radical copolymerization . First, dopamine (DP) was conjugated to the carboxylate groups of hyaluronic acid (HA).…”

Mussel‐Inspired Biocoating for Improving the Adhesion of Dental Pulp Stem Cells in Dental Pulp Regeneration

“…Simultaneously, hyaluronic acid (HA) is known for its existence in human body and good biocompatibility. [29][30][31] The combination of HA and DA might offer a stable DPSCs adhesion on the tooth slice, which could be used in pulp tissue regeneration. Herein, by…”