A Subdural Bioelectronic Implant to Record Electrical Activity from the Spinal Cord in Freely Moving Rats

Abstract

Bioelectronic devices have found use at the interface with neural tissue to investigate and treat nervous system disorders. Here, the development and characterization of a very thin flexible bioelectronic implant inserted along the thoracic spinal cord in rats directly in contact with and conformable to the dorsal surface of the spinal cord are presented. There is no negative impact on hind-limb functionality nor any change in the volume or shape of the spinal cord. The bioelectronic implant is maintained in rats for a period of 12 weeks. The first subdural recordings of spinal cord activity in freely moving animals are presented; rats are plugged in via a recording cable and allowed to freely behave and move around on a raised platform. Recordings contained multiple distinct voltage waveforms spatially localize to individual electrodes. This device has great potential to monitor electrical signaling in the spinal cord after an injury and in the future, this implant will facilitate the identification of biomarkers in spinal cord injury and recovery, while enabling the delivery of localized electroceutical and chemical treatments.

Multilayer Arrays for Neurotechnology Applications (MANTA): Chronically Stable Thin‐Film Intracortical Implants

“…Similar processes ( Figure a) have previously been used for micromanufacturing a large variety of neurotechnological devices, e.g., intraneural, epicortical, spinal cord, and intracortical interfaces, as well as retinal implants. [ 20,26–35 ]…”

“…As an alternative to exploring completely novel fabrication methods, we chose to refine an established photolithography process for PI microfabrication on wafer level, thereby leveraging over 30 years of experience addressing interlayer adhesion, interconnection, and functionalization of such probes. [20,[26][27][28][29][30][31][32][33][34][35] The process can be adapted to large-scale manufacturing and industrial batch production including parallel coating of PEDOT/PSS to further enhance the electrode properties.…”

“…To provide a figure of merit, Table 2 summarizes how track pitch (20 vs 6 μm) and number of separate routing layers (1-3) impact shank width, here using numbers that reflect typical PI processing scale, also our own previ-ous work. [20,26,35] The difference from the most simplistic process to the MANTAs, is at least a three times reduced shank width. "At least" is here appropriate as Table 2 neglects that tracks and electrodes often are routed in one and the same layer, meaning substantially widening the shanks even further emphasizing the value of layering.…”

“…Similar processes (Figure 1a) have previously been used for micromanufacturing a large variety of neurotechnological devices, e.g., intraneural, epicortical, spinal cord, and intracortical interfaces, as well as retinal implants. [20,[26][27][28][29][30][31][32][33][34][35] With the goal of making probes whose surfaces could be densely covered with electrodes, several adaptions were made to the base recipe (Figure 1b,c). First, we extended the process from the typical two-layer design to five individual insulation layers (each 2 μm) and four separate metallization layers (each 100 nm).…”

Highly Conformable Chip-in-Foil Implants for Neural Applications

“…Polyimides (PI) exhibit excellent chemical stability and biocompatibility, desirable mechanical properties, low water uptake leading to reduced plasticization, high electric resistivity and dielectric strength and are among the most used substrate materials for new generation mechanically compliant implants [14][15][16][17] . They are excellent substrate materials for exible neural implants as they are able to conform to curvilinear structures such as the brain 18 , are compatible with microfabrication processes and can be manufactured in sub micrometer thickness, and their high performance and long-term stability have been shown in several studies [19][20][21][22][23][24][25] .…”