Ionic conductive hydrogels have attracted extensive attention in the field of wearable sensing due to their excellent performance. However, most wearable sensors based on ionic conductive hydrogels focus on the detection of a single form of the human signal such as strain and pressure detection. To realize the comprehensive detection of human signals, the thermosensitive materials N-isopropylacrylamide (NIPAM) and acrylamide (AAm) were chemically cross-linked, and gelatin (GA) and tannic acid (TA) were introduced to construct a double-network structure hydrogel with tensile and temperature-sensing capabilities close to those of human skin. By adjusting the content of hydrophilic and hydrophobic segments of NIPAM and AAm in the first network of the hydrogel, the phase transition temperature could be controlled to realize real-time human temperature monitoring. The introduction of gelatin GA as the second network and TA as the hydrogen bond physical cross-linking center endow the hydrogel skin-like tensile strength (43 kPa) and toughness (33 kJ/m3) to adapt to the external strain changes in wearable sensing applications. Based on the skin-matching mechanical properties and good conductivity, the epidermal electrode assembled by the hydrogel had low interface impedance and excellent stability, which could be used for real-time collection of dynamic electrocardiogram (ECG) and electromyogram (EMG) physiological signals. It is believed that this hydrogel will provide new ideas for the design and manufacture of wearable devices for comprehensive health monitoring and telemedicine.
Jian Liu,Weizhong Xu,Zhongwen Kuang,Pengli Dong,Youxing Yao,Huaping Wu,Aiping Liu,Fangmin Ye
Smart hydrogels play a vital role in fundamental research and industrial applications in the fields of biosensors, flexible devices and intelligent human–machine technologies; however, developing a simple, low-cost and large-scale method to obtain hydrogel actuators with rapid response and robust and steadily controllable motion remains a big challenge. In this work, a temperature-responsive, gradient structured hydrogel with quick bending and adjustable actuation was fabricated by the copolymerization of the N-isopropylacrylamide (NIPAM) monomer with dispersed montmorillonite (MMT) via a facile precipitation method. The introduction of MMT with good thermal conductivity made the volume phase transition of the PNIPAM-based hydrogel occur earlier, and the deformation degree and bending direction could be adjusted by changing the MMT content. The representative composite hydrogel with 0.2 g MMT in the precursor presented bidirectional bending characteristics with a bending amplitude of about 289° and an average bending speed of about 36.0° s−1, while the composite hydrogel with 0.3 g MMT in the precursor only possessed a unidirectional bending ability with a bending amplitude of about −259° and a bending velocity of about −28.8° s−1 due to the great difference in the shrinking capacity between the top and bottom sides of the composite hydrogel. In addition, flexibly controllable deformation was specially realized by a well-designed patterned hydrogel with a local component and a thickness difference. Our work provides a practical method for the ingenious design of a hydrogel for further development of programmable and versatile hydrogel-based smart actuators and soft robots.
危险品化学品经营许可证（带存储）