Self-adhesive, ionic conductive, environmentally tolerant, and antibacterial phytic acid-reinforced zwitterionic hydrogels as flexible sensor applications

Ionic conductive hydrogels have attracted tremendous research interest for their intrinsic characteristics in the field of flexible sensors. However, the combination of multifunctionalities of high mechanical strength, satisfactory self-adhesiveness, ionic conductivity, anti-freezing, antibacterial properties, and biocompatibility remains a great challenge for the development of ionic conductive hydrogels. In this study, a novel ionic conductive hydrogel was developed by introducing highly conductive phytic acid (PA) to poly(sulfobetaine methacrylate) (polySBMA). PA molecules, as non-covalent crosslinkers and electrolytes in the polySBMA network, significantly improved the mechanical properties, self-adhesion, and electrical properties of the hydrogels. The optimal hydrogel displayed robust mechanical properties (tensile stress: 240.7 kPa), desirable adhesive strength (18.6 kPa to pig skin), and excellent ionic conductivity (2.44 S/m). Simultaneously, the presence of PA confers hydrogels with good antibacterial, anti-freezing properties and long-term environmental stability, and the hydrogels could remain soft even at -40 °C. Moreover, the hydrogel-based sensors showed high sensitivity (gauge factor up to 9.72), wide sensing range (≈400%), good stability, and accuracy for physical and physiological signals (tensile strain, pressure, fluid types and concentrations). This work has not only provided a simple strategy for fabricating tough and recoverable zwitterionic hydrogels, but also demonstrated the multifunctional properties of the zwitterionic hydrogels, which possess a great potential to fulfill flexible device applications.