A dry release of polyimide electrodes using Kapton film and application to EEG signal measurements

We describe here a simple and novel method to fabricate polyimide (PI) electrodes without a complex process to release completed PI electrodes from the substrates after full-curing process. We separated the PI electrodes from the Si-wafer prior to full-curing process, and these non full-cured electrodes were placed between the Kapton films, and we performed full-curing process with these sandwiched electrodes. Then, PI electrodes were easily and clearly released from the substrate without the sacrificial layers. We assessed the mechanical properties of fabricated electrodes comparing with non full-cured PI electrodes to investigate the full-curing effect between Kapton films. The electrical property was evaluated by measuring the impedance. Testing of the cyto-toxicity of full-cured electrodes using human mesenchymal stem cells (hMSCs) and mouse fibroblasts (L929) was carried out and the electrodes fabricated by proposed method were nontoxic and could be used as implantable electrodes. We also found that the electrodes, uniformly spread on the surface of mouse skulls while maintaining close contact, could successfully measure multichannel EEG signals.