In vivo electrochemical characterization of tissue-electrode interface during metamorphic growth

The domestication of insect locomotion has been recently investigated through microelectrode based systems implanted in the insect to tap into its neuromuscular system. Benefiting from developmental changes, the idea of performing such surgical implantation during metamorphic development enabled the fusion of engineered constructs to these living biological organisms. This study uses electrochemical analysis to provide a preliminary quantitative comparison of tissue-electrode coupling over the course of metamorphic development and after eclosion, where PEDOT:PSS coated gold electrodes are implanted in the insect during the early pupal stages and right after emergence. An average 1 kHz impedance of 8.9 k was obtained with pupal stage inserted electrodes, with a stored charge of 52 mC/cm2 at the interface as characterized by cyclic voltammetry 10 days after emergence. 5.1 mC/cm2 of this charge was successfully injected into the tissue through charge balanced biphasic pulses. In comparison, implanted electrodes in the adult state caused a 1 kHz impedance of 12.1 k, where the stored charge was 38 mC/cm2 with an injectable charge amount of 3.5 mC/cm2. Finally, to shed light on possible reasons for improvement in the bioelectrical coupling, equivalent circuit models were formed and the extracted parameters were correlated with metamorphic development of pupal tissue.