Flexible and wearable strain sensors based on tough and self-adhesive ion conducting hydrogels

Wang, Zhenwu; Chen, Jing; Wang, Liufang; Gao, Guorong; Zhou, Yang; Wang, Rong; Xu, Ting; Yin, Jingbo; Fu, Jun

doi:10.1039/c8tb02629g

Cited by 170 publications

(116 citation statements)

References 40 publications

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“…b–g) Mechanical performance of PVA‐CNF organoydrogels. b) The tensile stress–strain curves of PVA‐CNF organohydrogels with varying CNF contents, c) Stress and Young's modulus values of PVA‐CNF organohydrogels with varying CNF contents, d) Strain and toughness values of PVA‐CNF organohydrogels with varying CNF contents, e) Ashby plots of stress and strain values of reported ionic conducting (organo)hydrogels, including 1‐ethyl‐3‐methylimidazolium dicyanamide/poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) ([EMIm][DCA]/PAMPS) organohydrogel, [ 29 ] polyethylene glycol (PEG)/poly(acrylamide‐co‐acrylic acid) (PAMAA) hydrogel, [ 30 ] hydroxylpropyl cellulose/PVA hydrogel, [ 7b ] poly(styrene‐b‐ethylene oxide‐b‐styrene) (SOS) with 1‐ethyl‐3‐methylimidazolium bis(trifluoromethyl)sulfonyl amide ([EMI][TFSA]) organohydrogel, [ 31 ] PVA/poly[2‐(methacryloyloxy)ethyl]dimethyl‐(3‐sulfopropyl)]PSBMA hydrogel, [ 32 ] and PAM‐PEGDMA hydrogel, [ 5b ] f) Compressive stress–strain curves of PVA‐CNF organohydrogels with varying CNF contents. g) Cyclic compressive stress–strain curves of PVA‐1% CNF organohydrogel.…”

Section: Resultsmentioning

confidence: 99%

Cellulose Nanofibrils Enhanced, Strong, Stretchable, Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

Zhang

Chen

et al. 2020

Adv Funct Materials

525

420

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To date, ionic conducting hydrogel attracts tremendous attention as an alternative to the conventional rigid metallic conductors in fabricating flexible devices, owing to their intrinsic characteristics. However, simultaneous realization of high stiffness, toughness, ionic conductivity, and freezing tolerance through a simple approach is still a challenge. Here, a novel highly stretchable (up to 660%), strong (up to 2.1 MPa), tough (5.25 MJ m−3), and transparent (up to 90%) ionic conductive (3.2 S m−1) organohydrogel is facilely fabricated, through sol–gel transition of polyvinyl alcohol and cellulose nanofibrils (CNFs) in dimethyl sulfoxide‐water solvent system. The ionic conductive organohydrogel presents superior freezing tolerance, remaining flexible and conductive (1.1 S m−1) even at −70 °C, as compared to the other reported anti‐freezing ionic conductive (organo)hydrogel. Notably, this material design demonstrates synergistic effect of CNFs in boosting both mechanical properties and ionic conductivity, tackling a long‐standing dilemma among strength, toughness, and ionic conductivity for the ionic conducting hydrogel. In addition, the organohydrogel displays high sensitivity toward both tensile and compressive deformation and based on which multi‐functional sensors are assembled to detect human body movement with high sensitivity, stability, and durability. This novel organohydrogel is envisioned to function as a versatile platform for multi‐functional sensors in the future.

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Section: Resultsmentioning

confidence: 99%

Cellulose Nanofibrils Enhanced, Strong, Stretchable, Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

Zhang

Chen

et al. 2020

Adv Funct Materials

525

420

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“…Hydrogels are three‐dimensional (3D) polymeric networks with good stretchability, viscoelasticity, and swelling properties . Due to their outstanding performance, many stretchable hydrogels have been increasingly applied to the field of wearable strain sensors . For instance, Li et al developed a dual physically cross‐linked polymer hydrogel with hydrogen bonding and ionic coordination.…”

mentioning

confidence: 99%

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

Bei

Huang

et al. 2019

Macromol. Rapid Commun.

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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), ...

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“…The use of hydrogel has garnered great attention as a means of improvements in adhesion that leave no residue after detachment. [105,[206][207][208][209][210] Figure 8f shows one example of hydrogels that are very durable and adhesive, inspired by the delaminated structure of the skin. [105] In situ polymerization of nucleobasedriven adhesive hydrogels on the conductive tough hydrogels resulted in robust direct adhesion to the skin as well as various solid materials.…”

Section: Adhesionmentioning

confidence: 99%

Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment

et al. 2019

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glasses, watches, wristbands, or belts, are either fully or partially composed of planar and rigid materials, which require the use of obtrusive, hard supports or additional bendable strips to be mounted on the human body. Therefore, clinical devices that use the existing wearables cause discomfort and limit monitoring of human physiological data in the laboratory. This is the big limitation factor to overcome despite the ever-growing market for wearables in broader screenings outside of the clinic. By this account, it is necessary to replace the bulky and rigid plastics and metal components in the sensors and electronics with skin-like materials for enhanced wearability and functionality.The concept of WFHE poses a possible solution to address the aforementioned difficulties by providing user comfort, compliant mechanics, soft integration, multifunctionality, and smart diagnostics with embedded machine learning algorithms. Specifically, such electronics would provide stable and intimate contact to the soft human skin without adding any mechanical and thermal loadings or causing skin breakdown. Current development strategies and approaches for advanced WFHE focus on soft, flexible form factors, nonirritating and nontoxic characteristics, fully autonomous energy components, seamless wireless communications, Recent advances in soft materials and system integration technologies have provided a unique opportunity to design various types of wearable flexible hybrid electronics (WFHE) for advanced human healthcare and humanmachine interfaces. The hybrid integration of soft and biocompatible materials with miniaturized wireless wearable systems is undoubtedly an attractiveprospect in the sense that the successful device performance requires high degrees of mechanical flexibility, sensing capability, and user-friendly simplicity. Here, the most up-to-date materials, sensors, and system-packaging technologies to develop advanced WFHE are provided. Details of mechanical, electrical, physicochemical, and biocompatible properties are discussed with integrated sensor applications in healthcare, energy, and environment. In addition, limitations of the current materials are discussed, as well as key challenges and the future direction of WFHE. Collectively, an all-inclusive review of the newly developed WFHE along with a summary of imperative requirements of material properties, sensor capabilities, electronics performance, and skin integrations is provided. Wearable Flexible Hybrid ElectronicsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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Flexible and wearable strain sensors based on tough and self-adhesive ion conducting hydrogels

Abstract: Tough and self-adhesive zwitterionic hydrogels with ionic conductivity have been prepared, showing high and linear strain sensitivity for detecting human motions.

Cited by 170 publications

References 40 publications

Cellulose Nanofibrils Enhanced, Strong, Stretchable, Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

Cellulose Nanofibrils Enhanced, Strong, Stretchable, Freezing‐Tolerant Ionic Conductive Organohydrogel for Multi‐Functional Sensors

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

Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment

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