A Truly Injectable Neural Stimulation Electrode Made from an In-Body Curing Polymer/Metal Composite

Abstract

<jats:title>Abstract</jats:title><jats:p>Implanted neural stimulation and recording devices hold vast potential to treat a variety of neurological conditions, but the invasiveness, complexity, and cost of the implantation procedure greatly reduce access to an otherwise promising therapeutic approach. To address this need, we have developed a novel electrode that begins as an uncured, flowable pre-polymer that can be injected around a neuroanatomical target to minimize surgical manipulation. Referred to as the Injectrode, the electrode conforms to target structures forming an electrically conductive interface which is orders of magnitude less stiff than conventional neuromodulation electrodes. To validate the Injectrode, we performed detailed electrochemical and microscopy characterization of its material properties and validated the feasibility of using it to electrically stimulate the nervous system in rats and swine. The silicone-metal-particle composite performed very similarly to pure wire of the same metal (silver) in all measures, including exhibiting a favorable cathodic charge storage capacity (CSC<jats:sub>C</jats:sub>) and charge injection limits compared to the clinical LivaNova stimulation electrode and silver wire electrodes. By virtue of being simpler than traditional electrode designs, less invasive, and more cost-effective, the Injectrode has the potential to increase the adoption of neuromodulation therapies for existing and new indications.</jats:p>

Tissue Response to Neural Implants: The Use of Model Systems Toward New Design Solutions of Implantable Microelectrodes

“…However, it must be highlighted that not all the microelectrode types exhibit the same degradation profile or that there is a direct correlation between electrode failure and the acute inflammatory response (Gaire et al, 2018a). Several efforts have been reported to overcome the drawbacks from the mechanical mismatch between electrode and tissue by implementing materials with lower Young’s modulus, e.g., flexible and biocompatible polymer substrates (Trevathan et al, 2019). Polyimide- (Lai et al, 2012) and parylene-based MEMS (Hess et al, 2011) electrodes have been heavily investigated for their improved mechanical properties, easy access to fabricate, and capability to introduce bioactive molecules at the interface to facilitate long-term interaction with the tissue.…”

Computational modeling of dorsal root ganglion stimulation using an Injectrode

“…The Injectrode is composed of a platinum/iridium micro coil, which is designed to be introduced through a needle (18g, 1.27mm) and positioned around a specific neuroanatomical target. Once in place, it assumes a highly conforming and flexible structure, creating a clinical-grade electrode platform [26,43,53]. This unique design is intended to allow the Injectrode to conform around the target neuroanatomy, enabling access to challenging anatomical sites, including the DRG.…”

“…The Injectrode is a tightly wound polymer coated platinum/iridium microcoil which is injected via an 18-gauge needle near a neural target where it forms a highly conforming, flexible, clinical-grade electrode platform [26,54]. The Injectrode consists of three continuous regions: an uninsulated portion at one end to serve as a stimulation site, an insulated lead portion in the middle, and another uninsulated portion at the other end to serve as a subcutaneous charge collector [43].…”

There and Back Again: Building Systems That Integrate, Interface, and Interact with the Human Body

“…Stemming from this, groups have utilized injectable methods for placement, [47] even actively polymerizing material at the insertion site. [48][49][50] Other researchers have begun to develop soft robotic approaches to aid in placement of devices inside the body. [51] These techniques show some of the most promising current results for limiting or even eliminating the foreign body response.…”