Conducting polymer electrodes for auditory brainstem implants

Abstract

The auditory brainstem implant (ABI) restores hearing in patients with damaged auditory nerves. One of the main ideas to improve the efficacy of ABIs is to increase spatial specificity of stimulation, in order to minimize extra-auditory side-effects and to maximize the tonotopy of stimulation. This study reports on the development of a microfabricated conformable electrode array with small (100 μm diameter) electrode sites. The latter are coated with a conducting polymer, PEDOT:PSS, to offer high charge injection properties and to safely stimulate the auditory system with small stimulation sites. We report on the design and fabrication of the polymer implant, and characterize the coatings in physiological conditions in vitro and under mechanical deformation. We characterize the coating electrochemically and during bending tests. We present a proof of principle experiment where the auditory system is efficiently activated by the flexible polymeric interface in a rat model. These results demonstrate the potential of using conducting polymer coatings on small electrode sites for electrochemically safe and efficient stimulation of the central auditory system.

Electrodeposited PEDOT:Nafion Composite for Neural Recording and Stimulation

“…Potential transient responses were measured under cathodic‐first charge‐balanced biphasic pulses with 500 µs pulse duration followed by 100 µs interphase delay. The charge injection limit was obtained by continuously increasing the current amplitude until the cathodic polarization voltage reached −0.6 V versus Ag/AgCl . Stability tests were conducted by applying a continuous strain with the current pulse used to collect voltage transients (current amplitude = 150 µA) at 500 Hz for 3 million stimulations.…”

A conductive stretchable PEDOT–elastomer hybrid with versatile processing and properties

“…CPs are suited for a number of biological applications, ranging from electrode interfaces to controlled drug delivery devices. 3,4 Furthermore, the ability of CPs to conduct ions allows them to interact directly with biological systems. 1 As such, CPs show great promise as the next generation of electrodes to interface with biological tissues.…”

Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design

“…28 Materials such as polydimethylsiloxane that have been studied in animal models of the ABI and spinal cord have both stretchable and flexible properties and can theoretically achieve full conformability to the complex surface of the CN. 15,16 Measures of global curvature also provide important information that will influence device design. As discussed in the introduction, the thickness of an array influences how curved of a surface it can conform to.…”

“…The functionality, durability, and biocompatibility of these arrays have been tested in primate and rodent models of the ABI and of spinal cord injury. 15,16 In a spinal cord rodent model, flexible arrays were associated with reduced inflammation and deformation of the neural interface compared with rigid designs. 16 Polymers used in these substrates can be engineered to match the elastic properties of neural tissue and their flexibility can be tuned to better approximate the curved brain or spinal cord surface.…”

“…16 Polymers used in these substrates can be engineered to match the elastic properties of neural tissue and their flexibility can be tuned to better approximate the curved brain or spinal cord surface. 15,17,18 The ability of these arrays to conform to a surface is due to a physical phenomenon termed "capillarity-induced folding." 19 This phenomenon dictates that the elasticity and thickness of the material or sheet (in this study-ABI array) determine how curved of a surface the array can conform to.…”