Multi-characteristic tannic acid-reinforced polyacrylamide/sodium carboxymethyl cellulose ionic hydrogel strain sensor for human-machine interaction

A Transparent and Robust Ionogel with Stress-Induced Microphase Separation Property and Crack Insensitivity for Visual Force Sensor

Gel with ionic conductivity and stretchability is considered as an ideal alternative to conventional rigid metallic conductors in the flexible electronics. However, present gels suffer from poor mechanical properties and crack sensitivity due to their weak intermolecular (chain) interactions and homogeneous network structure. Herein, a transparent and tough polyacrylamide (PAM) ionogel is designed, which can form stress-induced microphase-separated domains with high hydrogen bonding density under stress to inhibit crack propagation. Benefiting from multiple hydrogen bonding interactions, the PAM ionogel exhibited maximum tensile stress of 5.19 ± 0.52 MPa, maximum tensile strain of 685.49 ± 22.15%, and fracture toughness of 10.11 ± 1.63 kJ m-2. On the other hand, the visual force sensor is realized by utilizing the stress-induced changes in the grayscale and electrical resistance of the PAM ionogel, which allowed real-time and visual monitoring of the stress applied to an object as a whole or in part. This work may open new avenues for the development of stable and reliable flexible sensors.

All-Textile Piezoelectric Nanogenerator Based on 3D Knitted Fabric Electrode for Wearable Applications

Flexible, air permeable and elastic self-powered sensors for human motion monitoring and assisted medical rehabilitation have recently become a hot research topic. However, most current piezoelectric sensors can not account for many characteristics. Addressing this challenge, an all-textile piezoelectric sensor (ATPS) based on 3D structured knitted fabric electrodes is reported. The ATPS consists of a piezoelectric element polyvinylidene fluoride nanofiber membrane, flexible knitted fabric electrodes, and an elastic self-adhesive bandage. Based on the flexible and efficient knitting technology, the sensor has the advantages of low cost, flexibility, simple structure, and convenient large-area manufacturing. Experimental and finite element simulation results show that the knitting pattern of fabric electrodes can enhance the piezoelectric output of ATPS. The optimal ATPS has a high voltage response sensitivity of up to 0.68 V/kPa. The proposed ATPS responds to a wide range of input forces from 0.098 to 724 N in self-powered mode, verifying its feasibility as a tactile sensor for human motion detection and recognition (throat swallowing, wrist bending, elbow bending, knee bending, walking slowly, running fast) and as a pressure sensor (Morse code, digit recognition) and demonstrating its potential for motion tracking, medical rehabilitation, and human-computer interaction.

Cellulose nanocrystals boosted hydrophobically associated self-healable conductive hydrogels for the application of strain sensors and electronic devices

Currently, hydrogel-based flexible devices become hot areas for scientists in the field of electronic devices, artificial intelligence, human motion detection, and electronic skin. These devices show responses to external stimuli (mechanical signals) and convert them into electrical signals (resistance, current, and voltage). However, the applications of the hydrogel-based sensor are hampered due to low mechanical properties, high time response, low fatigue resistance, low self-healing nature, and low sensing range. Herein, a strain sensing conductive hydrogel constructed from the CNCs (cellulose nanocrystal) reinforced, in which acrylamide and butyl acrylate work as hydrophilic and hydrophobic monomers respectively. The incorporation of CNCs in the polymeric system has a direct effect on their mechanical properties. The hydrogel having a high amount of CNCs (C4), its fracture stress and fracture strain reached 371.2 kPa and 2108 % respectively as well as self-healing of C4 hydrogel Broke at 499 % strain and bore 197 kPa stress. The elastic behavior of the hydrogels was confirmed by the rheological parameter frequency sweep and strain amplitude. Besides this our designed hydrogel shows an excellent response to deformation with conductivity 420 mS m-1, shows response to small strain (10 %) and large (400 %) strain, and has excellent anti-fatigue resistance with continuous stretching for 700 s at 300 % strain, with 140 msec response time, and gauge factor 7.4 at 750 % strain. The C4 hydrogel can also work as electronic skin when it is applied to different joints like the finger, elbow, neck, etc. The prepared hydrogel can also work as an electronic pen when it is worn to a plastic pen cover.