3D printable high-performance conducting polymer hydrogel for all-hydrogel bioelectronic interfaces.

Owing to the unique combination of electrical conductivity and tissue-like mechanical properties, conducting polymer hydrogels have emerged as a promising candidate for bioelectronic interfacing with biological systems. However, despite the recent advances, the development of hydrogels with both excellent electrical and mechanical properties in physiological environments is still challenging. Here we report a bi-continuous conducting polymer hydrogel that simultaneously achieves high electrical conductivity (over 11 S cm-1), stretchability (over 400%) and fracture toughness (over 3,300 J m-2) in physiological environments and is readily applicable to advanced fabrication methods including 3D printing. Enabled by these properties, we further demonstrate multi-material 3D printing of monolithic all-hydrogel bioelectronic interfaces for long-term electrophysiological recording and stimulation of various organs in rat models.

Highly fluorescent triazolopyridine-thiophene D-A-D oligomers for efficient pH sensing both in solution and in the solid state.

Conjugated fluorophores have been extensively used for fluorescence sensing of various substances in the field of life processes and environmental science, due to their noninvasiveness, sensitivity, simplicity and rapidity. Most existing conjugated fluorophores exhibit excellent light-emitting performance in dilute solutions, but their properties substantially decrease or even completely vanish due to severe aggregation quenching in the solid state. Herein, we synthesize a series of triazolopyridine-thiophene donor-acceptor-donor (D-A-D) type conjugated molecules with high absolute fluorescence quantum yields (ΦF) ranging from 80% to 89% in solution. These molecules also show unusual light-emitting properties in the solid state with ΦF of up to 26%. We find that owing to the protonation-deprotonation process of the pyridine ring, these compounds display obvious changes in both fluorescence wavelength and intensity upon addition of acids, and these changes can be readily recovered by the successive introduction of bases. By harnessing this phenomenon, we further show that these fluorophores can be employed for efficient and reversible fluorescence sensing of hydrogen ions in a broad pH range (0.0-7.0). With the fabrication of pH testing papers and ink-printed complex patterns including butterflies and letters on substrates, we demonstrate the application of such sensors to fluorescence indication or solid state pH detection for real samples such as volatile acidic/basic gas and water-quality analysis.

High-sensitivity and ultralow-hysteresis fluorine-rich ionogel strain sensors for multi-environment contact and contactless sensing.

Information transduction via soft strain sensors under harsh conditions such as marine, oily liquid, vacuum, and extreme temperatures without excess encapsulation facilitates modern scientific and military exploration. However, most reported soft strain sensors struggle to meet these requirements, especially in complex environments. Herein, a class of fluorine-rich ionogels with tunable ultimate strain, high conductivity, and multi-environment tolerance are designed. Abundant ion-dipole and dipole-dipole interactions lead to excellent miscibility between the hydrophobic ionic liquid and the fluorinated polyacrylate matrix, as well as adhesion to diverse substrates in amphibious environments. The ionogel-based sensors, even in encapsulation-free form, exhibit stable operation with a negligible hysteresis (as low as 0.119%) and high sensitivity (gauge factor of up to 6.54) under amphibious conditions. Multi-environment sensing instances in contact and even contactless forms are also demonstrated. This study opens the door for the artificial syntheses of multi-environment tolerance ionic skins with robust sensing applications in soft electronics and robotics.

Microstructured Polyfluoroacrylate Elastomeric Dielectric Layer for Highly Stretchable Wide-Range Capacitive Pressure Sensors.

Capacitive pressure sensors capable of replicating human tactile senses have garnered tremendous attention. Introducing microstructures into the dielectric layer is an effective approach to improve the sensitivity of the sensors. However, most reported processes to fabricate microstructured dielectric layers are complicated and time-consuming and usually have adverse effects on the mechanical properties. Herein, we report a mechanically strong and highly stretchable dielectric layer fabricated from a microstructured fluorinated elastomer with a high dielectric constant (5.8 at 1000 Hz) via a simple and low-cost thermal decomposition process. Capacitive pressure sensors based on this microstructured fluorinated elastomer dielectric layer and soft ionotronic electrodes illustrate an impressing stretchability (>300%), a high pressure sensitivity (17 MPa-1), a wide detection range (70 Pa-800 kPa), and a fast response time (below 300 ms). Moreover, the multipixel capacitive pressure sensors sensing array maintains the unique spatial tactile sensing performance even under significant tensile deformation. It is believed that our microstructured fluorinated elastomer dielectric layer might find wide applications in stretchable ionotronic devices.

High-Stretchability, Ultralow-Hysteresis ConductingPolymer Hydrogel Strain Sensors for Soft Machines.

Highly stretchable strain sensors based on conducting polymer hydrogel are rapidly emerging as a promising candidate toward diverse wearable skins and sensing devices for soft machines. However, due to the intrinsic limitations of low stretchability and large hysteresis, existing strain sensors cannot fully exploit their potential when used in wearable or robotic systems. Here, a conducting polymer hydrogel strain sensor exhibiting both ultimate strain (300%) and negligible hysteresis (<1.5%) is presented. This is achieved through a unique microphase semiseparated network design by compositing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) nanofibers with poly(vinyl alcohol) (PVA) and facile fabrication by combining 3D printing and successive freeze-thawing. The overall superior performances of the strain sensor including stretchability, linearity, cyclic stability, and robustness against mechanical twisting and pressing are systematically characterized. The integration and application of such strain sensor with electronic skins are further demonstrated to measure various physiological signals, identify hand gestures, enable a soft gripper for objection recognition, and remote control of an industrial robot. This work may offer both promising conducting polymer hydrogels with enhanced sensing functionalities and technical platforms toward stretchable electronic skins and intelligent robotic systems.

PEDOT-Based Conducting Polymer Actuators.

Conducting polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT) and its complex with poly(styrene sulfonate) (PEDOT:PSS), provide a promising materials platform to develop soft actuators or artificial muscles. To date, PEDOT-based actuators are available in the field of bionics, biomedicine, smart textiles, microactuators, and other functional applications. Compared to other conducting polymers, PEDOT provides higher conductivity and chemical stability, lower density and operating voltages, and the dispersion of PEDOT with PSS further enriches performances in solubility, hydrophility, processability, and flexibility, making them advantageous in actuator-based applications. However, the actuators fabricated by PEDOT-based materials are still in their infancy, with many unknowns and challenges that require more comprehensive understanding for their current and future development. This review is aimed at providing a comprehensive understanding of the actuation mechanisms, performance evaluation criteria, processing technologies and configurations, and the most recent progress of materials development and applications. Lastly, we also elaborate on future opportunities for improving and exploiting PEDOT-based actuators.