Conducting polymer hydrogels (CPHs) have emerged as a fascinating class of smart soft matters important for various advanced applications. However, achieving the synergistic characteristics of conductivity, self-healing ability, biocompatibility, viscoelasticity, and high mechanical performance still remains a critical challenge. Here, we develop for the first time a type of multifunctional hybrid CPHs based on a viscoelastic polyvinyl alcohol (PVA)-borax (PB) gel matrix and nanostructured CNFs-PPy (cellulose nanofibers-polypyrrole) complexes that synergizes the biotemplate role of CNFs and the conductive nature of PPy. The CNF-PPy complexes are synthesized through in situ oxidative polymerization of pyrrole on the surface of CNF templates, which are further well-dispersed into the PB matrix to synthesize homogeneous CNF-PPy/PB hybrid hydrogels. The CNF-PPy complexes not only tangle with PVA chains though hydrogen bonds, but also form reversibly cross-linked complexes with borate ions. The multi-complexation between each component leads to the formation of a hierarchical three-dimensional network. The CNF-PPy/PB-3 hydrogel prepared by 2.0 wt % of PVA, 0.4 wt % of borax, and CNF-PPy complexes with a mass ratio of 3.75/1 exhibits the highest viscoelasticity and mechanical strength. Because of a combined reinforcing and conductive network inside the hydrogel, its maximum storage modulus (∼0.1 MPa) and nominal compression stress (∼22 MPa) are 60 and 2240 times higher than those of pure CNF/PB hydrogel, respectively. The CNF-PPy/PB-3 electrode with a conductivity of 3.65 ± 0.08 S m has a maximum specific capacitance of 236.9 F g, and its specific capacitance degradation is less than 14% after 1500 cycles. The CNF-PPy/PB hybrid hydrogels also demonstrate attractive characteristics, including high water content (∼94%), low density (∼1.2 g cm), excellent biocompatibility, plasticity, pH sensitivity, and rapid self-healing ability without additional external stimuli. Taken together, the combination of such unique properties endows the newly developed CPHs with potential applications in flexible bioelectronics and provides a practical platform to design multifunctional smart soft materials.
Flexible
sensors have attracted great research interest due to
their applications in artificial intelligence, wearable electronics,
and personal health management. However, due to the inherent brittleness
of common hydrogels, preparing a hydrogel-based sensor integrated
with excellent flexibility, self-recovery, and antifatigue properties
still remains a challenge to date. In this study, a type of physically
and chemically dual-cross-linked conductive hydrogels based on 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO)-oxidized cellulose nanofiber (TOCN)-carrying carbon nanotubes
(CNTs) and polyacrylamide (PAAM) matrix via a facial one-pot free-radical
polymerization is developed for multifunctional wearable sensing application.
Inside the hierarchical gel network, TOCNs not only serve as the nanoreinforcement
with a toughening effect but also efficiently assist the homogeneous
distribution of CNTs in the hydrogel matrix. The optimized TOCN-CNT/PAAM
hydrogel integrates high compressive (∼2.55 MPa at 60% strain)
and tensile (∼0.15 MPa) strength, excellent intrinsic self-recovery
property (recovery efficiency >92%), and antifatigue capacity under
both cyclic stretching and pressing. The multifunctional sensors assembled
by the hydrogel exhibit both high strain sensitivity (gauge factor ≈11.8
at 100–200% strain) and good pressure sensing ability over
a large pressure range (0–140 kPa), which can effectively detect
the subtle and large-scale human motions through repeatable and stable
electrical signals even after 100 loading–unloading cycles.
The comprehensive performance of the TOCN-CNT/PAAM hydrogel-based
sensor is superior to those of most gel-based sensors previously reported,
indicating its potential applications in multifunctional sensing devices
for healthcare systems and human motion monitoring.
The human skin, an important sensory organ, responds sensitively to external stimuli under various harsh conditions. However, the simultaneous achievement of mechanical/thermal sensitivity and extreme environmental tolerance remains an enormous challenge for skin‐like hydrogel‐based sensors. In this study, a novel skin‐inspired hydrogel–elastomer hybrid with a sandwich structure and strong interfacial bonding for mechanical–thermal multimode sensing applications is developed. An inner‐layered ionic hydrogel with a semi‐interpenetrating network is prepared using sodium carboxymethyl cellulose (CMC) as a nanofiller, lithium chloride (LiCl) as an ionic transport conductor, and polyacrylamide (PAM) as a polymer matrix. The outer‐layered polydimethylsiloxane (PDMS) elastomers fully encapsulating the hydrogel endow the hybrids with improved mechanical properties, intrinsic waterproofness, and long‐term water retention (>98%). The silane modification of the hydrogels and elastomers imparts the hybrids with enhanced interfacial bonding strength and integrity. The hybrids exhibit a high transmittance (~91.2%), fatigue resistance, and biocompatibility. The multifunctional sensors assembled from the hybrids realize real‐time temperature (temperature coefficient of resistance, approximately −1.1% °C−1) responsiveness, wide‐range strain sensing capability (gauge factor, ~3.8) over a wide temperature range (from −20°C to 60°C), and underwater information transmission. Notably, the dual‐parameter sensor can recognize the superimposed signals of temperature and strain. The designed prototype sensor arrays can detect the magnitude and spatial distribution of forces and temperatures. The comprehensive performance of the sensor prepared via a facile method is superior to that of most similar sensors previously reported. Finally, this study develops a new material platform for monitoring human health in extreme environments.
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