Highly Stretchable and Biocompatible Strain Sensors Based on Mussel-Inspired Super-Adhesive Self-Healing Hydrogels for Human Motion Monitoring

Abstract

Integrating multifunctionality such as adhesiveness, stretchability, and self-healing ability on a single hydrogel has been a challenge and is a highly desired development for various applications including electronic skin, wound dressings, and wearable devices. In this study, a novel hydrogel was synthesized by incorporating polydopamine-coated talc (PDA-talc) nanoflakes into a polyacrylamide (PAM) hydrogel inspired by the natural mussel adhesive mechanism. Dopamine molecules were intercalated into talc and oxidized, which enhanced the dispersion of talc and preserved catechol groups in the hydrogel. The resulting dopamine-talc-PAM (DTPAM) hydrogel showed a remarkable stretchability, with over 1000% extension and a recovery rate over 99%. It also displayed strong adhesiveness to various substrates, including human skin, and the adhesion strength surpassed that of commercial double-sided tape and glue sticks, even as the hydrogel dehydrated over time. Moreover, the DTPAM hydrogel could rapidly self-heal and regain its mechanical properties without needing any external stimuli. It showed excellent biocompatibility and improved cell affinity to human fibroblasts compared to the PAM hydrogel. When used as a strain sensor, the DTPAM hydrogel showed high sensitivity, with a gauge factor of 0.693 at 1000% strain, and was capable of monitoring various human motions such as the bending of a finger, knee, or elbow and taking a deep breath. Therefore, this hydrogel displays favorable attributes and is highly suitable for use in human-friendly biological devices.

Properties of conductive polymer hydrogels and their application in sensors

“…reported a biocompatible strain sensor based on adhesive PAM hydrogel [Fig. (f)] . The hydrogel has good adhesion to different substrates of pigskin, test tube, hand, leaf, and glass [Fig.…”

“…(g) The adhesion measurements of the PAM hydrogel (Reproduced from Ref. , with permission from [2018 American Chemical Society]) (h) Schematic illustration synthetic process of composite hydrogel. (i) Nonplanar pressure sensing of the composite hydrogel sensor.…”

“…8(f)]. 94 The hydrogel has good adhesion to different substrates of pigskin, test tube, hand, leaf, and glass [ Fig. 8(g)].…”

Metal‐Free and Stretchable Conductive Hydrogels for High Transparent Conductive Film and Flexible Strain Sensor with High Sensitivity

“…[ 37 ] Especially, its 3D network structure is helpful of the diffusion of small molecules, ions, and current conduction. [ 38,39 ] Flexible materials have properties of softness, low modulus, and easy deformation, such as polyvinyl alcohol (PVA), [ 40,41 ] chitosan (CS). [ 42–44 ] Sensors assembled from flexible materials has excellent flexibility, bending freely and folding, and its structure is flexible and diverse.…”

Synthesis and Properties of Magnetic Self‐Healing Polymers: An Effective Method for Improving Interface Compatibility of Doped Functional Polymers

“…Magnetic nano materials [14,15] have been regarded as newlydeveloping materials due to its superior properties and has been widely applied in many fields such as mechanical electronics, military, biology, medical science, et al [16][17][18][19][20][21][22] In all magnetic nano materials, Fe 3 O 4 nanospheres (NPs) are thought to be the best for its advantages in stability, magnetic properties, biocompatibility, easy fabrication and low cost. Recently, many researchers have applied Fe 3 O 4 NPs into self-healing polymers such as elastomers, sensors, actuators, rubbers and instance synthetic polymers to fabrication magnetic self-healing polymers, [23][24][25][26][27][28][29][30] which can also be repaired when added an external magnetic field after it is damaged. Zhang [31] developed a magnetic self-healing hydrogel based on Fe 3 O 4 NPs materials to make hydrogel controllable and can be used for drug delivery, separation, remote controlled actuators.…”