Skin‐Inspired Multifunctional Autonomic‐Intrinsic Conductive Self‐Healing Hydrogels with Pressure Sensitivity, Stretchability, and 3D Printability

Abstract

The advent of conductive self-healing (CSH) hydrogels, a class of novel materials mimicking human skin, may change the trajectory of the industrial process because of their potential applications in soft robots, biomimetic prostheses, and health-monitoring systems. Here, the development of a mechanically and electrically self-healing hydrogel based on physically and chemically cross-linked networks is reported. The autonomous intrinsic self-healing of the hydrogel is attained through dynamic ionic interactions between carboxylic groups of poly(acrylic acid) and ferric ions. A covalent cross-linking is used to support the mechanical structure of the hydrogel. Establishing a fair balance between the chemical and physical cross-linking networks together with the conductive nanostructure of polypyrrole networks leads to a double network hydrogel with bulk conductivity, mechanical and electrical self-healing properties (100% mechanical recovery in 2 min), ultrastretchability (1500%), and pressure sensitivity. The practical potential of CSH hydrogels is further revealed by their application in human motion detection and their 3D-printing performance.

Untethered soft robotics

“…This enables highly compliant devices that exploit bulk conductivity, such as soft touch panels 113 ( Fig. 4k), underwater DEAs 65 , pulse and respiration sensors 114 , and even stretchable electroluminescent displays and sensors 7 (Fig. 4l).…”

A skin-like stretchable colorimetric temperature sensor

“…5b, pure PDMS film possessed a tensile Young's modulus, ultimate tensile strength and elongation at break of 1 MPa, 1.8 MPa and 150%, respectively. By comparison, the blue-phase PDA could sustain up to~300% stretch- [41], double network gel (DN gel) [42], poly(N-acryloyl glycinamide) gel (PNAGA gel) [43], polyurethane (PEU gel) [44], polypyrrole-grafted chitosan gel (DCh-Ppy gel) [45], nanocomposite hydrogels (NC gel) [46], hydrophobic association hydrogels (HA gel) [47], bacterial cellulose gel (BC gel) [48] and skin [49][50][51].…”

Self-Healing and Damage Resilience for Soft Robotics: A Review

“…A common thread among recent examples is the use of metal ions as a key to both the self-healing chemistry and the conductive element (Darabi et al, 2017;Lei et al, 2017;Liu and Li, 2017;. Though adding metal ions increases the conductivity of the hydrogels, researchers have carefully tuned the concentration: too low and the hydrogel does not conduct, too high and either the flexibility of the hydrogel is reduced or it ceases to self-heal.…”