Thermoelectric Hydrogel Electronic Skin for Passive Multimodal Physiological Perception

Electronic skins (e-skins) are being extensively researched for their ability to recognize physiological data and deliver feedback via electrical signals. However, their wide range of applications is frequently restricted by the indispensableness of external power supplies and single sensory function. Here, we report a passive multimodal e-skin for real-time human health assessment based on a thermoelectric hydrogel. The hydrogel network consists of poly(vinyl alcohol)/low acyl gellan gum with [Fe(CN)6]4-/3- as the redox couple. The introduction of glycerol and Li+ furnishes the gel-based e-skin with antidrying and antifreezing properties, a thermopower of 2.04 mV K-1, fast self-healing in less than 10 min, and high conductivity of 2.56 S m-1. As a prospective application, the e-skin can actively perceive multimodal physiological signals without the need for decoupling, including body temperature, pulse rate, and sweat content, in real time by synergistically coupling sensing and transduction. This work offers a scientific basis and designs an approach to develop passive multimodal e-skins and promotes the application of wearable electronics in advanced intelligent medicine.

Engineering pH responsive carboxyethyl chitosan and oxidized pectin -based hydrogels with self-healing, biodegradable and antibacterial properties for wound healing

As an important organ of the human body, effective protection of the skin during trauma is crucial. An ideal wound dressing should have adhesion, adsorption of wound secretions, and good antibacterial properties. Two kinds of natural polysaccharide-based hydrogels, carboxyethyl chitosan/oxidized pectin hydrogel (CEC/OP) and carboxyethyl chitosan/oxidized pectin/polyethyleneimine hydrogel (CEC/OP/PEI), were reported by using carboxyethyl chitosan as the matrix, and oxidized pectin and branched polyethyleneimine as the crosslinking agents. Both hydrogels could be formed in a short time and exhibited the pH responsively due to the presence of imine bond. Compared with carboxyethyl chitosan/oxidized pectin hydrogel, polyethyleneimine containing hydrogel can form gel quickly, a more compact and stable three-dimensional space network structure was formed, which exhibited better swelling performance, the swelling ration, rheology property, self-repair ability, and antibacterial performance. When the mass fractions of carboxyethyl chitosan and oxidized pectin solutions are 4 wt% and 9 wt%, respectively, the hydrogel exhibited an antibacterial efficiency of >96 % against both Staphylococcus aureus and Escherichia coli. After adding 0.75 wt% polyethyleneimine, the antibacterial efficiency of hydrogel could reach up to >98 %. More importantly, the polyethyleneimine containing hydrogel has a significant effect in the treatment of bacterially infected wounds.

Tough Adhesive, Antifreezing, and Antidrying Natural Globulin-Based Organohydrogels for Strain Sensors

Hydrogels are often used to fabricate strain sensors; however, they also suffer from freezing at low temperatures and become dry during long-time storage. Encapsulation of hydrogels with elastomers is one of the methods to solve these problems although the adhesion between hydrogels and elastomers is usually low. In this work, using bovine serum protein (BSA) as the natural globulin model and glycerol/H₂O as the mixture solvent, BSA/polyacrylamide organohydrogels (BSA/PAAm OHGs) were prepared by a facile photopolymerization approach. At the optimal condition, BSA/PAAm OHG demonstrated not only high toughness but also tough adhesion properties, which could strongly adhere to various substrates, such as glass, metals, rigid polymeric materials (even poly(tetrafluoroethylene), i.e., PTFE), and soft elastomers. Moreover, BSA/PAAm OHG was flexible and showed tough adhesion at -20 °C. The toughening mechanism and the adhesive mechanism were proposed. On being encapsulated by poly(dimethylsiloxane) (PDMS), it illustrated good antidrying performance. After introducing a conductive filler, the encapsulated BSA/PAAm OHG could be used as a strain sensor to detect human motions. This work provides a better understanding of the adhesive mechanism of natural protein-based organohydrogels.