Conductive hydrogels are excellent candidates for the next-generation wearable materials and are being extensively investigated for their potential use in health monitoring devices, human–machine interfaces, and other fields. However, their relatively low mechanical strength and performance degradation due to swelling have presented challenges in their practical application. Inspired by the multiscale heterogeneous architecture of biological tissue, a dynamic cross-linked, ultra-tough, and high-sensitivity hydrogel with a swelling resistance characteristic was fabricated by the principle of multiple non-covalent interaction matching and a step-by-step construction strategy. A heterogeneous structure was constructed by the combination of a ‘soft’ hydrophobic-conjugated micro-region structural domain with inter/intra-molecular hydrogen bonding and π–π stacking along with ‘rigid’ cross-linking via strong ionic coordination interactions. Reversible cross-linking synergies and variations in the content of rigid and flexible components guaranteed the hydrogel to undergo flexible and efficient modulation of the structures and gain excellent mechanics, including elongation at break (>2000%), toughness (∼60 MJ m⁻³), and recovery (>88%). Notably, hydrogels displayed good anti-swelling properties even in solutions with different pH (pH 2–11) and solvents. Moreover, the hydrogel further exhibited fast response (47.4 ms) and high sensitivity due to the presence of dynamic ions (Fe³⁺, Na⁺, and Cl⁻); therefore, it was assembled into a sensor to detect various human motions and used as a signal transmitter for the encryption and decryption of information according to Morse code. This study provides basis for the development of a variety of robust and flexible conductive hydrogels with multifunctional sensing applications in next-generation wearable devices.

An injectable polyethylene glycol (PEG) hydrogel was successfully prepared via borate–catechol complexation using dopamine functionalized 4-armed PEG (4-arm-PEG-DA) and phenylboronic acid modified 4-armed PEG (4-arm-PEG-PBA). The hydrogel was formed within 10 s by mixing 15 wt% 4-arm-PEG-DA with 15 wt% 4-arm-PEG-PBA buffer solutions at pH 9.0. The hydrogel was characterized by Fourier transform infrared (FT-IR) spectroscopy, rheological measurements, scanning electron microscopy (SEM) and lap shear strength tests. Furthermore, pH, glucose and dopamine responsiveness of the hydrogel based on phenylborate–catechol complexation was demonstrated by degradation experiments and drug release tests. The lap shear strength tests indicated that the hydrogel possessed the ability of self-healing which was bestowed by the phenylborate–catechol dynamic covalent bond. Moreover, the hydrogel could serve as a decent bio-adhesive due to its adhesion properties on different substrates especially the porcine skin. In vitro cytotoxicity tests demonstrated the excellent cytocompatibility of the hydrogel. The results of all the experiments indicate that our newly developed multi-functionalized hydrogel can have potential applications in biomedical fields such as drug delivery, tissue engineering, and bio-adhesives.

Conductive materials with predominant mechanical properties and high sensitivity have promising applications in various fields such as fabrication of electric skins, wearable sensors, and soft robotics. High-performance and flexible strain sensors based on conductive hydrogels have attracted significant attention because of their potential applications in voice recognition and human–machine interfaces. Inspired by the mechanism of neural tissue signal transmission, herein, a high-strength and relatively high-sensitivity ionic conductive hydrogel was developed by utilizing the completely physically crosslinked polyvinyl alcohol (PVA) and a simple inorganic salt solution soaking strategy. The ionic conductive hydrogels exhibited intriguing remoldability and excellent mechanical properties such as superb tensile strength (8.03 MPa), high toughness (28.7 MJ m⁻³), and high elastic modulus (1 MPa) because of their high-density hydrogen bonding and chain entanglement networks. By integrating the PVA–NaCl gel into a flexible strain sensor, the sensor displayed high conductivity (7.14 S m⁻¹) at room temperature and subzero temperature, high accuracy (GF = 0.989), and sensitive strain responsiveness in a wide strain detection window of 0.2–400%. These results imply good performance for monitoring and distinguishing various human daily activities and slight physiological signals. Furthermore, the as-made PVA sol could convert to gel state just by being injected on a flexible substrate under an ice-bath and the conductive hydrogels displayed excellent biocompatibility and improved cell proliferation. Therefore, the as-formulated hydrogel sensor can have promising applications in wearable devices, such as sports monitoring, healthcare monitoring or voice recognition.

Conductive hydrogels have drawn tremendous attention in flexible devices, soft robotics, and artificial intelligence. The integration of synergistic characteristics such as reliable resilience, high strain sensitivity, and excellent mechanical properties is still a great challenge in strain sensors. Inspired by the heterogeneous network structure of biological soft tissues, herein, a novel ionic conductive hydrogel was fabricated by the interconnection between a “soft” hydrogen bond cross-linked polymeric network and “rigid” domains cross-linked by double hydrogen bonding, hydrophobic interaction, and π–π stacking. The completely physically cross-linked hydrogel exhibited excellent stretchable property (680%) and great resilience (92.53%). Besides, owing to numerous free moving ions (Li⁺, Na⁺, and Cl⁻) in the system, the hydrogel possessed high sensitivity (GF = 3.12) and fast strain responsiveness (≤100 ms) in a broad temperature range (−20–25 °C). Moreover, the hydrogel displayed tunable electromechanical behavior with durable stability and anti-fatigue variations in resistance upon mechanical deformation such as the detection of various daily human activities, including the variations of the fingers, elbow and larynx, and, jogging. Therefore, this “soft and rigid” structure provides a feasible solution for fabricating a high-performance ionic conductive hydrogel, which has potential as a multi-functional sensor in wearable devices, artificial intelligence, and electric skins.

The development of temperature-responsive and biodegradable polymeric nanoparticles with tunable temperature sensitivity is of great interest. In this study, alternating polyurethanes were synthesized from diisocyanate (L-lysine ethyl ester diisocyanate (LDI) or hexamethylene diisocyanate (HDI)) and poly(ethylene glycol) (PEG) of different molecular weights. The resulting polyurethanes were then used to prepare nanoparticles either by direct dispersion in water or by nanoprecipitation. The temperature-responsive property of the polyurethane nanoparticles was evaluated by UV-visible transmittance experiments and dynamic light scattering. During the heating–cooling cycling, the LDI-PEG series showed almost no change except LDI-PEG600, but the HDI-PEG series exhibited reversible dispersion–aggregation changes. The nanoparticles were spherical at temperatures below or above the cloud point, as observed by transmission electron microscopy. The cloud point temperature of the alternative polymers was found to depend on both the hydrophilic–hydrophobic balance of the alternative chain and polymer concentration. The degradation test in vitro revealed a fall of less than 20% of polymer molecular weight within 12 days. The transition temperature was close to human body temperature, which could have great potential in biomedical fields.