Ultrastretchable and Highly Sensitive Hydrogel Strain Sensors by Electrohydrodynamic Direct-Writing

Hydrogels have advanced skin bioelectronic characteristics. However, obtaining flexible hydrogel strain sensors with good mechanical properties and accurate signaling remains a challenge. Here, acrylamide and sodium alginate monomers were mixed to construct a semi-interpenetrating network hydrogel, and cellulose nanocrystals were incorporated into the hydrogel network in order to enhance the mechanical and electrical characteristics of the hydrogel material. The shaping of the hydrogel strain sensor was carried out by the electrohydrodynamic (EHD) printing method, and the manufacturing of the hydrogel strain sensor was completed by combining with the UV curing method. Owing to the external high-voltage electric field, ions underwent directional movement and cellulose nanocrystals were aligned, resulting in the fabrication of hydrogel strain sensors with high conductivity (1.9 mS cm-1), exceptional sensitivity (gauge factor of 2.17 at 100% strain), minimal hysteresis (dissipation energy of 1.38 kJ m-3 at 100% strain), and excellent long-term stability. Moreover, the fabricated hydrogel strain sensor was applied to monitor movements of human body parts and transmit writing signals in real time, which indicates that the hydrogel strain sensor prepared by the electrohydrodynamic printing method has great potential for wearable and human-computer interaction applications.