Stretchable Surface Electrode Arrays Using an Alginate/PEDOT:PSS-Based Conductive Hydrogel for Conformal Brain Interfacing

Abstract

An electrocorticogram (ECoG) is the electrical activity obtainable from the cerebral cortex and an informative source with considerable potential for future advanced applications in various brain−interfacing technologies. Considerable effort has been devoted to developing biocompatible, conformal, soft, and conductive interfacial materials for bridging devices and brain tissue; however, the implementation of brain−adaptive materials with optimized electrical and mechanical characteristics remains challenging. Herein, we present surface electrode arrays using the soft tough ionic conductive hydrogel (STICH). The newly proposed STICH features brain−adaptive softness with Young’s modulus of ~9.46 kPa, which is sufficient to form a conformal interface with the cortex. Additionally, the STICH has high toughness of ~ 36.85 kJ/mm3, highlighting its robustness for maintaining the solid structure during interfacing with wet brain tissue. The stretchable metal electrodes with a wavy pattern printed on the elastomer were coated with the STICH as an interfacial layer, resulting in an improvement of the impedance from 60 kΩ to 10 kΩ at 1 kHz after coating. Acute in vivo experiments for ECoG monitoring were performed in anesthetized rodents, thereby successfully realizing conformal interfacing to the animal’s cortex and the sensitive recording of electrical activity using the STICH−coated electrodes, which exhibited a higher visual−evoked potential (VEP) amplitude than that of the control device.

Highly Conductive and Reusable Cellulose Hydrogels for Supercapacitor Applications

“…The circuit contained a 9-volt battery, a supercapacitor of the composite hydrogel, and an LED lamp connected in series, as shown in Figure 14 a. The LED operated with full intensity without any visible damage to the conductive hydrogel as shown in Figure 14 b, confirming the stand-alone properties of the hydrogel electrolyte [ 51 , 52 ]. The Na-Alginate/PEDOT:PSS composite electrolyte hydrogel improved the conductivity properties for supercapacitor cell applications [ 45 , 52 ].…”