Multi-Dimensional Fuzzy Graphene Bioelectronic Actuators

Abstract

The ability to manipulate the electrophysiology of electrically active cells and tissues has enabled a deeper understanding of healthy and diseased states. This has primarily been achieved via bioelectronic actuators that interface engineered materials with biological entities. Graphene has gained recent interest as a building-block for bioelectronic actuators due to its advantageous electrochemical properties and biocompatibility. However, functional graphene bioelectronics exhibit a two-dimensional (2D) topology. This leads to inherent performance limitations due to the limited exposed surface-area and poor interactions with interfaced cells and tissues. Ideal geometry of graphene-based actuators needs to leverage the material’s high surface-area-to-volume ratio to facilitate maximum interaction with the electrode.Here we report a breakthrough three-dimensional (3D) topology of graphene: nanowire templated 3D fuzzy graphene (NT-3DFG), for actuation of electrically active cells and tissues. Using a bottom-up approach, we synthesize an interconnected network of free-standing graphene flakes on Si nanowires (SiNWs). The 3D topology leads to enhanced surface-area compared to planar surfaces allowing NT-3DFG microelectrodes to exhibit lower electrode impedance. The increased surface area also leads to an increase of up to 5-fold and 10-fold in the cathodic charge storage capacity (CSCC) and the charge injection capacity (CIC), respectively, for 20 µm NT-3DFG compared to 20 µm conventional Pt electrodes. To enhance the electrical actuation capabilities of NT-3DFG, we electrodeposit poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) on the 3D electrodes. This results in further enhancement in the exhibited CSCC and CIC thus enabling further miniaturization of graphene-based microelectrodes to ultra-microelectrodes for functional bioelectronics. Our results demonstrate the importance of extending the topology of nanomaterials to 3D to push the physical and functional limits of conventional bioelectronics.