Printed, Flexible pH Sensor Hydrogels for Wet Environments

Current sensors for monitoring environmental signals, such as pH, are often made from rigid materials that are incompatible with soft biological tissues. The high stiffness of such materials sets practical limitations on the in situ utilization of sensors under biological conditions. This article describes a soft yet robust hydrogel‐based pH sensor that can be 3D printed. The pH‐sensitive poly(3,4‐ethylenedioxythiophene) is combined with hydrophilic polyurethane to create novel printable inks with favorable biomechanical properties. These inks are employed to fabricate highly flexible pH sensors that linearly respond to pH in wet environments. The pH sensitive hydrogels can undergo extreme deformations including twisting, bending, and up to 400 extension cycles without any deterioration in their electrical properties. Such printable inks that can produce biosensors using a one‐step fabrication method eliminate the cumbersome and inconvenient processing of rigid materials that are used in the manufacturing of conventional pH sensors.