Tough, Antifreezing, and Piezoelectric Organohydrogel as a Flexible Wearable Sensor for Human-Machine Interaction.

Piezoelectric hydrogel sensors are becoming increasingly popular for wearable sensing applications due to their high sensitivity, self-powered performance, and simple preparation process. However, conventional piezoelectric hydrogels lack antifreezing properties and are thus confronted with the liability of rupture in low temperatures owing to the use of water as the dispersion medium. Herein, a kind of piezoelectric organohydrogel that integrates piezoelectricity, low-temperature tolerance, mechanical robustness, and stable electrical performance is reported by using poly(vinylidene fluoride) (PVDF), acrylonitrile (AN), acrylamide (AAm), p-styrenesulfonate (NaSS), glycerol, and zinc chloride. In detail, the dipolar interaction of the PVDF chain with the PAN chain facilitates the crystal phase transition of PVDF from the α to ß phase, which endows the organohydrogels with a high piezoelectric constant d33 of 35 pC/N. In addition, the organohydrogels are highly ductile and can withstand significant tensile and compressive forces through the synergy of the dipolar interaction and amide hydrogen bonding. Besides, by incorporating glycerol and zinc chloride, the growth of ice crystals is inhibited, allowing the organohydrogels to maintain stable flexibility and sensitivity even at -20 °C. The real-time monitoring of the pulse signal for up to 2 min indicates that the gel sensor has stable sensitivity. It is believed that our organohydrogels will have good prospects in future wearable electronics.

Soft, Super-Elastic, All-Polymer Piezoelectric Elastomer for Artificial Electronic Skin.

Piezoelectric sensors are widely used in wearable devices to mimic the functions of human skin. However, it is considerably challenging to develop soft piezoelectric materials that can exhibit high sensitivity, stretchability, super elasticity, and suitable modulus. In this study, a soft skin-like piezoelectric polymer elastomer composed of poly(vinylidene fluoride) (PVDF) and a novel elastic substrate polyacrylonitrile is prepared by combining the radical polymerization and freeze-drying processes. Dipole-dipole interaction results in the phase transition of PVDF (α phase to ß phase), which enhances the electrical and mechanical performances. Thus, we achieve a high piezoelectric coefficient (d33max = 63 pC/N), good stretchability (211.3-259.3%), super compressibility (subjected to 99% compression strain without cracking), and super elasticity (100% recovery after extreme compression) simultaneously for the elastomer. The soft composite elastomer produces excellent electrical signal output (Vocmax = 253 mV) and responds rapidly (15 ms) to stress-induced polarization effects. In addition, the elastomer-based sensor accurately detects various physiological signals such as gestures, throat vibrations, and pulse waves. The developed elastomers exhibit excellent mechanical properties and high sensitivity, which helps facilitate their application as artificial electronic skin to sense subtle external pressure in real time.

Plasmon-Enhanced Electrocatalysis of Conductive Polymer-Based Nano-Heterojunction for Small Molecule Metabolites Diagnostics.

Conductive polymers are promising electrode candidates in the nonenzymatic catalytic detection of small molecule metabolites, due to the tunable electronic conductivity and versatile modifiability. However, the complex catalytic reaction pathway of conductive polymers results in lower detection sensitivity and a narrower linear range compared with clinical metal-based and carbon-based electrodes. Localized surface plasmon resonance (LSPR), characterized by deep strong light-matter coupling, has great potential in driving surface catalytic reactions at an ultrafast rate. Here, we constructed a salix argyracea-like polypyrrole nanowires/silver nanoparticles (PPy/AgNPs) heterojunction electrode using polydopamine as a dopant and chelator. Through cyclic voltammetry, the Mott-Schottky curve, and COMSOL simulation, we demonstrated that the LSPR-excited photocarriers enhanced PPy/AgNPs electrode electrocatalysis. Thus, the detection current response and linear range were significantly improved under the LSPR excitation when taking glucose and hydrogen peroxide as models of small molecule metabolites. Furthermore, we discussed the LSPR-enhanced detection mechanism of PPy/AgNPs electrode from the aspects of the Tafel slope, the apparent electron diffusion coefficient, and the charge transfer resistance. This strategy opens a new avenue toward the design of LSPR-enhanced conductive polymer electrodes.

Strong Biopolymer-Based Nanocomposite Hydrogel Adhesives with Removability and Reusability for Damaged Tissue Closure and Healing.

Bioadhesives are widely used in a variety of medical settings due to their ease of use and efficient wound closure and repair. However, achieving both strong adhesion and removability/reusability is highly needed but challenging. Here, we reported an injectable mesoporous bioactive glass nanoparticle (MBGN)-incorporated biopolymer hydrogel bioadhesive that demonstrates a strong adhesion strength (up to 107.55 kPa) at physiological temperatures that is also removable and reusable. The incorporation of MBGNs in the biopolymer hydrogel significantly enhances the tissue adhesive strength due to an increased cohesive and adhesive property compared to the hydrogel adhesive alone. The detachment of bioadhesive results from temperature-induced weakening of interfacial adhesive strength. Moreover, the bioadhesive displays injectability, self-healing, and excellent biocompatibility. We demonstrate potential applications of the bioadhesive in vitro, ex vivo, and in vivo for hemostasis and intestinal leakage closure and accelerated skin wound healing compared to surgical wound closures. This work provides a novel design of strong and removable bioadhesives.