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

Abstract

Conductive hydrogels are ideal for flexible sensors, but it is still a challenge to produce such hydrogels with combined toughness, selfadhesion, self-healing, anti-freezing, moisturizing, and biocompatibility properties. Herein, inspired by natural skin, a highly stretchable, strainsensitive, and multi-environmental stable collagen-based conductive organohydrogel was constructed by using collagen (Col), acrylic acid, dialdehyde carboxymethyl cellulose, 1,3-propylene glycol, and AlCl 3 . 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 selfhealing 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.

Simple and Rapid Way to a Multifunctionally Conductive Hydrogel for Wearable Strain Sensors

“…Compared with the FTIR spectrum of the PAA hydrogel, a right shift peak around 3370 cm –1 was observed in the FTIR spectrum of the TA@Fe 3+ –PAA hydrogel, demonstrating the formation of stronger hydrogen bonds after introducing TA . Notably, there is a new absorption peak around 1632 cm –1 in the FTIR spectrum of the TA@Fe 3+ –PAA hydrogel, which is attributed to the Fe 3+ –COO – coordination bond …”

“…50 Notably, there is a new absorption peak around 1632 cm −1 in the FTIR spectrum of the TA@Fe 3+ −PAA hydrogel, which is attributed to the Fe 3+ −COO − coordination bond. 22 Mechanical Property Analysis. The mechanical properties of the TA@Fe 3+ −PAA hydrogel were systematically studied.…”

“…4−7 These superior characteristics have allowed them to be ideal candidates for diverse applications such as human−machine interfaces, 8 soft robots, 9 electrochromic devices, 10 supercapacitors, 11,12 implantable biosensors, 13 electrostimulated drug release units, 14 plant culture substrate, 15 human health monitoring, 16−18 tissue repair materials, 19,20 and artificial skin. 21 The preparation methods, however, have always been burdened by laborious and time-consuming manufacturing processes, 22 as well as the additional input of external energy, to satisfy all of these stringent requirements. 23−25 For example, the preparation strategy for polyacrylic acid (PAA)-based conductive hydrogels usually requires lots of time and energy for the cleavage of initiators such as ammonium persulfate (APS) to initiate the polymerization reaction.…”

“…Conductive hydrogels have recently received notable attention due to their numerous advantages, such as their excellent stretchability, high flexibility, soft-and-wet nature, , mechanical deformation, and environmental stimuli that can be converted into electrical signals. − These superior characteristics have allowed them to be ideal candidates for diverse applications such as human–machine interfaces, soft robots, electrochromic devices, supercapacitors, , implantable biosensors, electrostimulated drug release units, plant culture substrate, human health monitoring, − tissue repair materials, , and artificial skin . The preparation methods, however, have always been burdened by laborious and time-consuming manufacturing processes, as well as the additional input of external energy, to satisfy all of these stringent requirements. − For example, the preparation strategy for polyacrylic acid (PAA)-based conductive hydrogels usually requires lots of time and energy for the cleavage of initiators such as ammonium persulfate (APS) to initiate the polymerization reaction. − Especially, the prepared hydrogels displayed a huge deformation and even damage when exposed to external forces, which greatly reduced their sensitivity and service life. , To address this issue, the development of self-healing hydrogels has been extensively studied by introducing dynamic covalent bonding into the hydrogel network. , Due to their dynamic qualities and simplicity of synthesis, boronate ester linkages generated by the interaction of boronic acid with cis -diols have been frequently employed to prepare multifunctional hydrogels. , Lin et al, for example, reported a multiple sensing hydrogel via boronic ester bonds based on Ag/TA/CNC nanohybrids, PVA, and borax. The hydrogel possesses repeatable self-healing abilities since dynamic borate ester linkages between PVA and borax were established .…”

Self-healing hydrogels for bone defect repair

“…54,55 Owing to these excellent biological properties, hydrogels have been widely studied in tissue engineering, drug transport, and medical device research. [56][57][58][59][60][61][62] In addition, hydrogels are applied in wound dressings, [63][64][65] electronic equipment, 66 biosensor development, [67][68][69] cell imaging, 70 waste disposal, 71 and articial skin-like materials. [72][73][74] However, a lack of toughness, low mechanical strength and batch variation have limited the application of hydrogels in the medical eld.…”