Soft and flexible electroactive materials for neuroprosthetic devices

Abstract

Event Abstract Back to Event Soft and flexible electroactive materials for neuroprosthetic devices Josef Goding1, Rylie A. Green1 and Laura A. Poole-Warren1 1 University of New South Wales, Graduate School of Biomedical Engineering, Australia Since the inception of neuroprosthetic devices in the 1950’s with the development of cardiac pacemakers, metallic materials have been used to conduct and inject electrical charge in the body. Neuroprosthetic devices typically use platinum or gold electrodes to inject charge into the surrounding tissue[1]. These electrodes have several limitations including their high stiffness (contributes to chronic inflammatory response), low charge injection limits and their tendency to dissolve due to electrically initiated chemical reactions. Similarly, platinum-iridium and cobalt-chromium-molybdenum alloys are commonly used as electrode leads in devices such as cochlear implants and cardiac pacemakers. The poor flexural properties of these alloys can result in failure of the lead component. Additionally, due to the metal wires acting as antennae, these devices are often incompatible with MRI techniques. Conductive polymers (CPs) are a promising alternative to metallic materials for the conduction and delivery of therapeutic charge in the body. However, CPs are brittle and friable and have a limited number of compatible formation techniques[2]. In order to create a soft and flexible conductive material, this study investigated the use of the CP complex poly(3,4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) and polyurethane (PU) to fabricate conductive elastomers (CE). To fabricate the PU-PEDOT:PSS elastomer, various loadings of PEDOT:PSS were dispersed in a solution of PU dissolved in dimethylsulfoxide. The solution was cast and dried to produce a CE film. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to assess the charge storage capacity (CSC) and impedance of the CE films. Tensile tests were conducted to determine ultimate tensile strength (UTS) and elongation at fracture. Increasing the weight percent of PEDOT in the CE films from 8 to 24 wt% corresponded with an increase in CSC from 33 mC.cm-2 to 224 mC.cm-2 (Fig. 1). EIS revealed that all CE films had stable impedances between 0.1 Hz and 10 kHz with 0° phase angle below 1 kHz. Increasing the PEDOT content from 8 to 24 wt% corresponded with a decrease in impedance from 1608 Ω.cm-1 to 175 Ω.cm-1 (equivalent to 0.6 mS.cm-1 and 5.7 mS.cm-1 respectively). Tensile testing of the CEs proved they are capable of significant extension with the 8 wt% PEDOT CE capable of 480% extension with an UTS of 9.1 MPa (Fig. 2). Increasing the PEDOT content to 24 wt% decreased the toughness of the CE film with UTS and elongation reduced to 1.6 MPa and 90% respectively. Dispersing PEDOT:PSS throughout a PU network resulted in a soft, flexible, electrically active elastomer. The resulting CE is capable of conducting and injecting electrical charge, with increasing PEDOT:PSS content corresponding with increased CSC, decreased impedance and toughness. CEs hold great potential for use as flexible electrode arrays and leads due to their ideal electrochemical and mechanical properties and MRI compatibility. Future studies will focus on improving the conductivity of the CE films via elecrochemical depostion of CP within CE films as well as investigating the materials compatibility with conventional elastomer formation techniques.