Fully Passive Flexible Wireless Neural Recorder for the Acquisition of Neuropotentials from a Rat Model

Abstract

Wireless implantable neural interfaces can record high-resolution neuropotentials without constraining patient movement. Existing wireless systems often require intracranial wires to connect implanted electrodes to an external head stage or/and deploy an application-specific integrated circuit (ASIC), which is battery-powered or externally power-transferred, raising safety concerns such as infection, electronics failure, or heat-induced tissue damage. This work presents a biocompatible, flexible, implantable neural recorder capable of wireless acquisition of neuropotentials without wires, batteries, energy harvesting units, or active electronics. The recorder, fabricated on a thin polyimide substrate, features a small footprint of 9 mm × 8 mm × 0.3 mm and is composed of passive electronic components. The absence of active electronics on the device leads to near zero power consumption, inherently avoiding the catastrophic failure of active electronics. We performed both in vitro validation in a tissue-simulating phantom and in vivo validation in an epileptic rat. The fully passive wireless recorder was implanted under rat scalp to measure neuropotentials from its contact electrodes. The implanted wireless recorder demonstrated its capability to capture low voltage neuropotentials, including somatosensory evoked potentials (SSEPs), and interictal epileptiform discharges (IEDs). Wirelessly recorded SSEP and IED signals were directly compared to those from wired electrodes to demonstrate the efficacy of the wireless data. In addition, a convoluted neural network-based machine learning algorithm successfully achieved IED signal recognition accuracy as high as 100 and 91% in wired and wireless IED data, respectively. These results strongly support the fully passive wireless neural recorder's capability to measure neuropotentials as low as tens of microvolts. With further improvement, the recorder system presented in this work may find wide applications in future brain machine interface systems.

Wirelessly-Powered Cage Designs for Supporting Long-Term Experiments on Small Freely Behaving Animals in a Large Experimental Arena

“…Although most wirelessly-powered cages provide PTE and PDL for specific experimental conditions, the physical constraints of Rx coils, coil separations, and magnetic field homogeneity over the experimental area should be compared for a more suitable choice. As the most recent class of IMDs are millimeter-sized and distributed over a large area in the brain or the rest of the body [43][44][45][46], the importance of wirelessly-powered cages for tiny multiple implants is elevated as introduced in Section 4. Hence, it is important for designers to select suitable wirelessly-powered cages, considering the practical limitations of IMD design related to key aspects, such as PTE, PDL, closed-loop power control, scalability, spatial/angular misalignment, near-field data telemetry, and safety issues against various perturbations during the longitudinal animal experiment.…”

A Polyimide-Based Flexible Monopole Antenna Fed by a Coplanar Waveguide

“…In ref 7, a flexible, ultra-low profile, and compact dual band antenna was reported, which was inkjet-printed on a PI substrate and fed by coplanar waveguide. PI has a trend to be chosen as the substrate because it has more advantages in terms of cost performance, and it exhibits a good balance of physical, chemical, and electrical properties [5][6][7][8][9][10][11][12][13][14][15]. Major manufacturing technologies for CPW antennas on PI films include lithography [16] and printing [5][6][7]17,18], which rely on expensive equipment or strict experimental environment requirements [5][6][7][19][20][21][22], and the metal layers fabricated by these proposed methods easily crack and shed [23,24].…”

Flexible Bandpass Filter Fabricated on Polyimide Substrate by Surface Modification and In Situ Self-Metallization Technique

“…Polymers are suitable for use in the substrates of flexible electronics due to their excellent bendability, electrical properties, and other characteristics [1][2][3][4][5][6]. Among them, liquid crystal polymer (LCP) [1,2] and polyimide (PI) [3,4] have recently been widely used in substrates of flexible devices. PI is cheaper than LCP [7].…”