Hydrogel Based Implant Resonator for Wireless pH Sensing

This study introduces a pH-sensitive hydrogel-based implant resonator for real time, in-body sensing. The hydrogel's pH dependent dielectric and conductive properties enable its use as a passive microwave resonator, wirelessly interrogated via a wideband on-body reader antenna. The system, designed for chipless RFID-based communication, eliminates the need for active power sources in-body. It demonstrates high sensitivity to physiological pH changes, particularly relevant for postoperative infection detection, where wound pH shifts from 4.5-6 to 6.5-8 for healthy and infected respectively. Experimental results confirm that the dielectric properties of the hydrogel change with pH consistently with no hysteresis behavior, underscoring its potential for next-generation biomedical sensors in continuous health monitoring. It has been shown that the pH of the immediate surrounding of the hydrogel based sensor can be tracked with minimum of 5 MHz shifts for every 2-units of pH change.