New Hydrogel Multimodal Subdural Electrocorticographic Electrodes

The electrical activity of neurons in the brain controls everything from the routine regulation of muscle movements to intelligent operations such as memory,and these electrical activities are the main active representations of information transmission in the neural system.Therefore,how to record the electrical activity accurately is an important direction for the development of neuroscience.Subdural electrode has been widely used in neuroscience research and clinical medicine,and the subdural recording of electrocorticography(ECoG)can achieve the decoding of gesture information and the control of precision movements such as fingers,which has very good clinical application.However,the subdural electrodes are made of platinum-iridium alloy as a conductive material,which has a great mechanical mismatch with the neural tissue,causing brain damage and loss of function of the electrodes,and cannot be implanted safe in the long-term.Therefore,there is an urgent need to solve the biocompatibility of long-term implanted electrodes.In order to solve this problem,there are currently two directions:the first is to improve the metal part of the electrode by making it thinner and smaller;the other is to use new materials for conducting electricity instead of metal,such as graphene and polymers,but the modulus of elasticity of both materials is much larger than the brain tissue,resulting in compatibility problems.Either way,there is a long distance to make long-term clinical burial safe.Therefore,we propose to fabricate a flexible and conformable subdural electrode based on PDMS(polydimethylsiloxane)with a novel PVA(Polydimethylsiloxane)-ACSF(Artificial cerebrospinal fluid)hydrogel material as an ionic conductor.To simulate the chemical properties of brain tissue,we used ACSF as a solvent for the hydrogel,which provides free moving ions to charge the hydrogel.Our previous study demonstrated that hydrogel electrodes can record high signal-to-noise electrophysiological signals in the brain,and hydrogels have unique mechanical and chemical properties similar to those of biological tissues,thereby exhibiting excellent biocompatibility and greatly attenuating neuroinflammatory responses and brain tissue destruction.We recorded electrophysiological signals from anesthetized cats using this new hydrogel electrode.It has also been shown that hydrogel electrode cause much less glial hyperplasia and vascular destruction than conventional clinical subdural electrodes,and it is more suitable for long-term implantation.In addition,the electrode,due to its softness,can move with brain pulsation with less damage;its transparency is also suitable for combining with other optical imaging techniques.Since there is no metallic component,it is more suitable for signal detection in combination with MRI imaging.Our new hydrogel electrodes offer the possibility of combining multiple imaging techniques for clinical applications while recording electrophysiological signals,providing a new tool for the diagnosis and treatment of neurological diseases in the clinic.