Low-cost flexible printed circuit technology based microelectrode array for extracellular stimulation of the invertebrate locomotory system

The biobotic control of invertebrates through functional electrical stimulation of neural and neuromuscular tissue is under active exploration. Implantable microelectrodes are often designed to be used in chronic long term applications in vertebrates and subjected to strict endurance and resolution requirements. However, these constraints can be relaxed in invertebrate-related applications to allow low cost production for high-volume markets. In this study, we propose flexible printed circuit board (flex-PCB) based electrodes for implantable neuromuscular stimulation, address related shortcomings, and suggest modifications in the fabrication process. We were able to obtain a charge storage capacity of 3.18 mC/cm2 and 1 kHz impedance of 52 kΩ with gold electroplated 100 μm × 100 μm electrode sites on the flex-PCB electrodes. The electrodeposition of iridium oxide and electrochemical polymerization of PEDOT with dopant PSS on microelectrodes enhanced the charge storage capacity to 38.9 and 124.3 mC/cm2 where the 1 kHz impedance magnitude was 16 kΩ and 3 kΩ, respectively. This improvement in electrochemical performance was also corroborated by current pulsed voltage excursion studies. The long term dip test in saline solution supports the potential of flex-PCB electrodes for neural electrostimulation of insects, while revealing potential instability in PEDOT-PSS coatings with continuous high current density pulsing.