Dynamically crosslinked poly(vinyl alcohol)/borax strain sensors for organ motion monitoring

Wearable electronic sensing devices can detect various physiological responses and subtle changes in the skin in real time for the early detection and treatment of potential health problems or diseases. Among them, flexible hydrogel-based sensors are attracting much attention because they can monitor human movements and physiological signals. However, developing hydrogel-based sensors with rapid self-healing, self-adhesion, excellent conductivity and sensitivity characteristics remains a challenge. In this study, a hydrogel with a dynamic reversible network structure was developed using poly(vinyl alcohol) (PVA), hyaluronic acid (HA), borax, and tannic acid (TA). Multiple hydrogen bonds resulting from abundant hydroxyl groups in the hydrogel composed of borax, PVA, and TA improved the self-healing ability of the hydrogel, and the conductivity of this system (∼0.62 S/m) was improved upon immersion in NaCl. The optimum hydrogel exhibited excellent elasticity (∼941 %), biocompatibility, and demonstrated adhesion to porcine skin (dry: 5.3 kPa; wet: 2 kPa) without external stimulation in air and underwater environments. In addition, the fabricated hydrogels exhibited excellent sensitivity (∼300 % strain, gauge factor (GF) = 2.86; 300–900 % strain, GF = 4.95), allowing them to detect and distinguish various large and small human movements. Hydrogels that exhibited stable electrical signals even after 500 cycles were obtained, and the PBHT-N hydrogels were implanted into rabbit hearts to verify their applicability as strain sensors for effective real-time heart rate monitoring during rapid body movement.