Development of an Ultrastretchable Double-Network Hydrogel for Flexible Strain Sensors

Human beings cannot live without elastomers, which exist almost everywhere in human life nowadays. Although elastomers with a variety of features are developed for specific applications, a timeless topic is how to toughen them, because mechanical properties always determine the reliability and lifespan of the utilized elastomers. Toughening of a soft material has a long history and the main idea is widely accepted, i.e., building energy dissipation into the stretchy networks. Double network (DN) method is the most pioneering and representative practice of materials toughening, which is successfully applied to numerous hydrogel systems. Intensive studies on DN hydrogel systems are implemented and relevant reviews are well documented, whereas important reviews about DN elastomers are absent. In this review, recent progress on toughening elastomers using the DN strategy is reviewed. By reviewing the fabrication methods and relevant extensions, toughening mechanisms at different length scales, functionalities, and applications in sequence, it is shown how one polymer network plus another gives rise to a tough elastomer with superior mechanical properties. It is believed that this review can give some insight into existing DN elastomer systems and inspire the development of next‐generation tough soft materials.

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“…can be utilized to construct the first network of a hybrid DN hydrogel. [75][76][77][78][79][80][81][82][83][84]…”

Section: Physically/chemically Cross-linked Hybrid Dn Gelsmentioning

confidence: 99%

Recent Progress in Double Network Elastomers: One Plus One is Greater Than Two

Yang

Tang

et al. 2022

Adv Funct Materials

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“…[47] By taking advantage of the flexibility and stretchability of hydrogels, Azadi et al [48] developed a flexible sensor made of polyvinyl alcohol (PVA) nanocomposite with high stretchability up to 500% and a thin conductive hybrid layer of PVA/silver nanowires (AgNWs). Li et al [49] synthesized a 3D printable double network (DN) agar/acrylic acid (AAC) network-Fe 3+ hydrogel to reach a remarkable stretchability (3174.3%). In addition to wearable sensors, hydrogels are used in flow sensors to enhance sensitivity by covering the sensing element with hydrogel cupula; for instance, Kottapalli et al [50] developed a superficial neuromast-inspired flow sensor with a prolate formation spheroid-shaped hydrogel cupula.…”

Section: Introductionmentioning

confidence: 99%

Biomimetic Ultraflexible Piezoresistive Flow Sensor Based on Graphene Nanosheets and PVA Hydrogel

Moshizi

Moradi

et al. 2021

Adv Materials Technologies

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unmanned underwater robots, [3] sleep apnea treatment, [4] and other biomedical applications. [5] Among these, mimicking sensory hair cells that are ubiquitous in the creatures such as fish lateral line, crocodile body, locust's legs, mammalian vestibular system, and hearing system has attracted significant interest among many researchers. In nature, sensory hair cells work based on mechanical deflection induced by flow, vibration, acoustic vibration, and gravitational force, generating electrochemical signals and transmitting them to the brain. [6,7] The organs of balance (saccule, utricle, and semicircular canals) are filled with a fluid called the endolymph, which has a high concentration of potassium (K + ) ions and is low in sodium (Na + ) ions. When a linear or angular acceleration occurs, the ciliary tip links stretch or relax, depending on movement direction. In the case of the links stretching, the tip-links' channels are opened, allowing entry of particular cations (including potassium) into the cell, causing depolarization in the cell.

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“…[5,33] Thus they are endowed with many unique advantages, including intrinsic soft wet nature, good biocompatibility, and especially tissue-like mechanical properties, which have made polymeric hydrogels promising candidates for flexible sensors. [34] In this context, considerable progresses have been recently achieved in soft conductive hydrogels with strain-dependent electronic signal changes. However, it still remains challenging to develop the promising dual-channel hydrogel systems with both sensitive conductivity and interactive fluorescence color changes to dynamic activities, which would show potentials to enable both electronic and visual monitoring of human motions.…”

mentioning

confidence: 99%

Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

Lin

Wang

et al. 2022

Advanced Optical Materials

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such as carbon nanotubes, graphene, nanowires) into soft elastomer composites. [8][9][10][11][12][13][14][15][16] Nevertheless, most of these reported flexible strain sensors could only display one single electrical signal output, which might have some practical use limitations. Especially with the development of human-machine interactive systems, there has been an increasing demand for dual-channel reporting flexible sensors, which are capable of exhibiting both strain-dependent electrical and optical changes. [17][18][19][20][21] Among various optical means, fluorescence is believed to quite promising for wearable stretchable sensing uses because of its high sensitivity, fast response and operational simplicity. The most convenient strategy is to develop the mechanofluorescent elastomer materials with strain-dependent electrical signal response. One famous example was reported by Zhang and colleagues who draw inspiration from the muscle-controlled display tactics of cephalopods to present the robust nanostructured self-healable and mechanoluminescent elastomer composites, which were capable of displaying reversible strain-dependent luminescence and resistance response to tensile strain. [21] Meanwhile, there has also been a growing interest to explore soft polymeric hydrogels for flexible sensors. [22][23][24][25][26][27][28][29][30][31][32] Different from elastomers, polymeric hydrogels usually have a 3D crosslinked hydrophilic network that is highly swollen by water. [5,33] Thus they are endowed with many unique advantages, including intrinsic soft wet nature, good biocompatibility, and especially tissue-like mechanical properties, which have made polymeric hydrogels promising candidates for flexible sensors. [34] In this context, considerable progresses have been recently achieved in soft conductive hydrogels with strain-dependent electronic signal changes. However, it still remains challenging to develop the promising dual-channel hydrogel systems with both sensitive conductivity and interactive fluorescence color changes to dynamic activities, which would show potentials to enable both electronic and visual monitoring of human motions. This is possibly because it is quite difficult to construct robust multifunctional materials with continuous and synergistic fluorescence/electronic signal responses over a wide strain range.Flexible strain sensors are of great importance in many emerging applications for human motion monitoring, implanted devices, and humanmachine interactive systems. However, the dual-channel sensing systems that enable both strain-dependent electronic and visually optical signal responses still remain underdeveloped, but such systems are of great interest for human-machine interactive uses. Here, inspired by the mechanically modulated skin color changes of squids via muscle contracting/releasing movements, a class of mechanofluorescent and conductive hydrogel laminates for visually flexible electronics is presented. The sensing laminates consist of interfacially bonded red fluorescent hyd...

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Development of an Ultrastretchable Double-Network Hydrogel for Flexible Strain Sensors

Cited by 115 publications

References 51 publications

Recent Progress in Double Network Elastomers: One Plus One is Greater Than Two

Recent Progress in Double Network Elastomers: One Plus One is Greater Than Two

Biomimetic Ultraflexible Piezoresistive Flow Sensor Based on Graphene Nanosheets and PVA Hydrogel

Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

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