Soft, conformal PDMS-based ECoG electrode array for long-term in vivo applications

Electrocorticogram (ECoG) electrode arrays based on soft materials, such as polydimethylsiloxane (PDMS), are preferable because they can be implanted with better conformal contact and have physical properties close to biological tissues; thus, the adverse effects on tissues are minimal. However, the realization of electrodes in the micrometer scale on PDMS is challenging. Previously, parylene-treated PDMS was suggested as a solution and proven to be successful in acute in vivo applications. In this study, PDMS-based ECoG electrode arrays fabricated using parylene-treated PDMS (parylene-deposited PDMS and parylene-filled PDMS) are evaluated for the first time in terms of stability and reliability for long-term use. The mechanical and electrochemical properties are investigated over time for up to 8 months through accelerated aging. The ECoG electrode array, implanted in the primary somatosensory area of the brain, can successfully record somatosensory evoked potentials (SEPs) upon mechanical stimulus of the paws with sufficient spatial resolution to distinguish between forepaw and hindpaw stimulations. Finally, the PDMS-based electrodes demonstrate the feasibility of chronic recording for up to 3 months in non-human primates. Based on theses results, it is concluded that they can be used as promising materials and methods to develop various bio-integrated electronic devices that require softness, flexibility, conformability, and robustness over long-term.