Currently, flexible wearable hydrogel-based sensors have attracted considerable attention due to their promising applications in a variety of fields. However, concurrently integrating toughness, adhesiveness, self-healing ability, and conductivity into the hydrogel is still a great challenge. Here, casein sodium salt from bovine milk (sodium casein, SC) and polydopamine (PDA, inspired by mussels) were successfully introduced into the polyacrylamide (PAAm) hydrogel system to fabricate a tough and adhesive SC−PDA hydrogel. The hydrogel exhibits splendidly reversible adhesive behavioral bonding toward various materials and even human skin. Moreover, based on the dynamic cross-linking of SC and PDA in the system, the hydrogel has superstretching ability, excellent fatigue resistance, and rapid self-healing ability. In addition, the existence of sodium ions also endowed the SC−PDA hydrogel with sensitive deformation-dependent conductivity to act as a flexible strain and pressure sensor for directly monitoring large-scale human motions (e.g., joint bending) and tiny physiological signals (e.g., speaking and breathing). Therefore, the strategy would broaden the path of a new generation of hydrogel-based sensors for wide applications.
In recent years, nature-inspired conductive hydrogels have become ideal materials for the design of bioactuators, healthcare monitoring sensors, and flexible wearable devices. However, conductive hydrogels are often hindered by problems such as the poor mechanical property, nonreusability, and narrow operating temperature range.Here, a novel skin-inspired gel is prepared via one step of blending polyvinyl alcohol, gelatin, and glycerin. Due to their dermis-mimicking structure, the obtained gels possess high mechanical properties (fracture stress of 1044 kPa, fracture strain of 715%, Young's modulus of 157 kPa, and toughness of 3605 kJ m −3 ). Especially, the gels exhibit outstanding strainsensitive electric behavior as biosensors to monitor routine movement signals of the human body. Moreover, the gels with low temperature tolerance can maintain good conductivity and flexibility at −20 °C. Interestingly, the gels are capable of being recovered and reused by heating injection, cooling molding, and freezing−thawing cycles. Thus, as bionic materials, the gels have fascinating potential applications in various fields, such as human−machine interfaces, biosensors, and wearable devices.
Conductive hydrogels
had demonstrated significant prospect in the
field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature
falls below zero. Here, a novel conductive organohydrogel was developed
by introducing polyelectrolytes and glycerol into hydrogels. The gel
exhibited excellent elongation, self-healing, and self-adhesive performance
for various materials. Moreover, the gel could withstand a low temperature
of −20 °C for 24 h without freezing and still maintain
good conductivity and self-healing properties. As a result, the sample
could be applied for motion detection and signal transmission. For
example, it can respond to finger movements and transmit network signals
like network cables. Therefore, it was envisioned that the effective
design strategy for conductive organohydrogels with antifreezing,
toughness, self-healing, and self-adhesive properties would provide
wide applications of flexible wearable devices.
Breaking through the conventional way of conferring anti-icing ability on hydrogels with addition of organic solvents or inorganic salts, a novel anti-icing hydrogel driven by antifreeze proteins was successfully fabricated and applied as sensors.
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