Thermal safety considerations for implantable micro-coil design

Micro magnetic stimulation of the brain via implantable micro-coils is a promising novel technology for neuromodulation. Careful consideration of the thermodynamic profile of such devices is necessary for effective and safe designs. Objective. We seek to quantify the thermal profile of bent wire micro-coils in order to understand and mitigate thermal impacts of micro-coil stimulation. Approach. In this study, we use fine wire thermocouples and COMSOL finite element modeling to examine the profile of the thermal gradients generated near bent wire micro-coils submerged in a water bath during stimulation. We tested a range of stimulation parameters previously reported in the literature such as voltage amplitude, stimulus frequency, stimulus repetition rate and coil wire materials. Main results. We found temperature increases ranging from Significance. ISO standard 14708-1 designates a thermal safety limit of 2 & DEG;C temperature increase for active implantable medical devices. By switching the coil wire material from platinum/iridium to gold, our study achieved a 5-6-fold decrease in the thermal impact of coil stimulation. The thermal gradients generated from the gold wire coil were measured below the 2 & DEG;C safety limit for all stimulation parameters tested.

Automated summary

Micro magnetic stimulation of the brain via implantable micro-coils is a promising technology for neuromodulation, but careful consideration of the thermodynamic profile is necessary. This study used thermocouples and finite element modeling to examine the thermal gradients generated by bent wire micro-coils during stimulation. By switching coil wire material, the thermal impact of stimulation was significantly reduced below the safety limit.