Solution-Processable Conductive Composite Hydrogels with Multiple Synergetic Networks toward Wearable Pressure/Strain Sensors

Abstract

A biocompatible, flexible, yet robust conductive composite hydrogel (CCH) for wearable pressure/strain sensors has been achieved by an all-solution-based approach. The CCH is rationally constructed by in situ polymerization of aniline (An) monomers in the polyvinyl alcohol (PVA) matrix, followed by the cross-linking of PVA with glutaraldehyde (GA) as the cross-linker. The unique multiple synergetic networks in the CCH including strong chemical covalent bonds and abundance of weak physical cross-links, i.e., hydrogen bondings and electrostatic interactions, impart excellent mechanical strength (a fracture tensile strength of 1200 kPa), superior compressibility (ε = 80%@400 kPa), outstanding stretchability (a fracture strain of 670%), high sensitivity (0.62 kPa–1 at a pressure range of 0–1.0 kPa for pressure sensing and a gauge factor of 3.4 at a strain range of 0–300% for strain sensing, respectively), and prominent fatigue resistance (1500 cycling). As the flexible wearable sensor, the CCH is able to monitor different types of human motion and diagnostically distinguish speaking. As a proof of concept, a sensing device has been designed for the real-time detection of 2D distribution of weight or pressure, suggesting its promising potentials for electronic skin, human–machine interaction, and soft robot applications.

Flexible and wearable strain sensors based on conductive hydrogels

“…In this system, aldehyde groups (from GA) reacted with hydroxy groups (from PVA) and combined into acetyl groups to form chemical crosslinking, while phytic acid served as physical crosslinking sites to interact with PVA and PANI chains through hydrogen bonds. It should be noted that acid‐doped PANI would shift to a kind of positively charged structure 80–81 and form electrostatic interaction with phytic acid (as shown in Figure 9E, from Ref.). It's also should be pointed out that polymerization of aniline is not a classical chain‐growth mechanism 82 .…”

“…For instance, Wei and coworkers 80 synthesized a PANI‐based hydrogel through a simple method: they firstly added the aniline monomer into an aqueous solution containing PVA and phytic acid, and sequentially the aniline monomer was initiated by ammonium persulfate (APS) to polymerize into linear macromolecules of PANI. Finally, glutaraldehyde (GA) was added to crosslink with PVA chains to convert the polymer solution into the hydrogel.…”

Recent Progress in Conducting Polymer Composite/Nanofiber-Based Strain and Pressure Sensors

“…Phytic acid effectively served a dual role, i.e., acid dopant for in situ polymerization to form PANI and the catalyst for the cross-linking reaction of PVA. Strong chemical covalent bonds existing in PVA/phytic acid and PVA/glutaraldehyde, in addition to the weak physical crosslinks, i.e., hydrogen bonding and electrostatic interactions among PANI conductive networks, granting good toughness (2.5 MJ•m −3 ), and low elastic modulus (1.0 kPa), promoting them as wearable sensors [122]. Stretchability along with the reprocess ability and reshape ability achieved with reversible Diels-Alder-networked PU materials and the conductive PANI networks established with phytic acid dopants were in-situ polymerized.…”

Highly sensitive, weatherability strain and temperature sensors based on AgNPs@CNT composite polyvinyl hydrogel

“…Flexible sensors that respond to external stimuli such as temperature, humidity and deformation can be applied to the monitoring of human signs, such as body temperature, respiration, movement and so on. [1][2][3][4] A hydrogel is a potential exible sensing material, which has the advantages of good exibility, high biocompatibility and adjustable material composition. [5][6][7][8][9][10][11] Generally, conductive nanomaterials, such as carbon-based nanomaterials, [12][13][14] metal nanomaterials 15,16 and conductive polymers, 17,18 are oen used to form conductive networks in hydrogels, which can improve the conductivity and sensing properties of hydrogels.…”