In Situ Measurement of Stimulus Induced pH Changes Using ThinFilm Embedded IrOx pH Electrodes

The high complexity of the biological response to implanted materials builds a serious barrier against implanted recording and stimulation electrode arrays to succeed in clinically relevant chronic studies. Some of the cell and molecular interactions and their contribution to inflammation and device failure are still unclear. The interrelated mechanisms leading to tissue damage and electrode array failure during simultaneous faradaic, electrochemical reactions and biological response under electrical stimulation are not understood sufficiently. One variable, with which inflammatory and electrode surface processes can be analyzed and assessed, is the pH change in the immediate environment of the material-tissue interface. Here, the greatest challenges are in the biocompatibility and in-vivo long-term stability of selected sensor materials, the measurement of small transient pH oscillations and positioning of the sensor at a defined and nearest possible distance in the micrometer range, to the site of activity without the pH sensing being affected by the material- issue interactions itself. This work represents the in-situ measurement of local and transient pH changes at apulsed electrode with an embedded in-vivo compatible pH sensor and therein differentiating from current approaches of pH sensing during electrical stimulation.