Self-Healable Conductive Nanocellulose Nanocomposites for Biocompatible Electronic Skin Sensor Systems

Abstract

Electronic skins are developed for applications such as biomedical sensors, robotic prosthetics, and human–machine interactions, which raise the interest in composite materials that possess both flexibility and sensing properties. Polypyrrole-coated cellulose nanocrystals and cellulose nanofibers were prepared using iron­(III) chloride (FeCl3) oxidant, which were used to reinforce polyvinyl alcohol (PVA). The combination of weak H-bonds and iron coordination bonds and the synergistic effect of these components yielded self-healing nanocomposite films with robust mechanical strength (409% increase compared to pure PVA and high toughness up to 407.1%) and excellent adhesion (9670 times greater than its own weight) to various substrates in air and water. When damaged, the nanocomposite films displayed good mechanical (72.0–76.3%) and conductive (54.9–91.2%) recovery after a healing time of 30 min. More importantly, the flexible nanocomposites possessed high strain sensitivity under subtle strains (<48.5%) with a gauge factor (GF) of 2.52, which was relatively larger than the GF of ionic hydrogel-based skin sensors. These nanocomposite films possessed superior sensing performance for real-time monitoring of large and subtle human motions (finger bending motions, swallowing, and wrist pulse); thus, they have great potentials in health monitoring, smart flexible skin sensors. and wearable electronic devices.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

“…[ 257 ] Multifunctional properties were achieved, allowing self‐healing, conductivity, sensing, and also adhesion. [ 258 ] Even magnetic properties can be incorporated to hybrid gels. Agarose hydrogels containing CNF reinforcements decorated with conjugated polymer polypyrrole/Fe 3 O 4 facilitate conductivity and magnetically responsive materials.…”

“…[ 240 ] Hybrid gels were prepared using conjugated polypyrrole‐coated CNCs and CNFs, in order to reinforce PVA with Fe 3+ mediated coordinative crosslinks to provide adhesion ( Figure a). [ 258 ] Similarly, Al 3+ ‐ion mediated coordination bonds allow hybrid hydrogels with adhesion. [ 215 ] CNF hybrid hydrogels with PNIPAm facilitate reversible optical, bioadhesion, and thermal performance, making them suitable to be used as durable temperature‐sensitive sensors and functional biomedical devices.…”

“…Reproduced with permission. [ 258 ] Copyright 2019, American Chemical Society. b) Evaporation‐induced deposition of CNC for anisotropic gluing layers leads to strong adhesion in‐plane but weak adhesion out‐of‐plane.…”

Flexible Self‐Repairing Materials for Wearable Sensing Applications: Elastomers and Hydrogels

“…Among them, the gel deformation ability was improved by adding polystyrene particles, the adhesion of various interfaces was achieved by doping polydopamine nanoparticles, and the gel conductivity was endowed by adding lithium chloride as shown in Figure 8b,d. [133] In addition, selfhealing conductive hydrogels composed of conductive ions and conductive polymers have outstanding performance in tensile strength, such as Fe 3+ /polypyrrole composite conductive hydrogels [135,136] with much higher tensile strength than Fe 3+ conductive hydrogels. [124,125] The sensitivity of self-healing flexible sensors is crucial in practical applications.…”

Ultrathin and Robust Micro–Nano Composite Coating for Implantable Pressure Sensor Encapsulation

“… 21 , 32 , 33 Biocompatible with human bodies. 16 , 34 − 36 Minimal effect on the sensor performances: the measurement error and sensitivity of the sensor should be almost intact after encapsulation. 2 , 22 , 37 − 41 …”