Recording Properties and Biocompatibility of Chronically Implanted Polymer-based Intrafascicular Electrodes

Abstract

We implanted polymer-based longitudinal intrafascicular electrodes (polyLIFEs) in feline dorsal rootlets acutely and for periods of two to six months to evaluate their electrical properties and biocompatibility. A total of 38 implanted electrodes were analyzed. Some 25 of the 38 electrodes were implanted with an insulative flexible polymer cuff, which was required for recording of afferent activity in situ. Electrode impedances remained stable for the duration of the experiments. The distributions of axons were measured at three levels of the implanted rootlets: the implant level, 1-2 mm proximal to the implant with respect to the cell body, and 1-2 mm distal to the implant with respect to the cell body. Similar measurements were made in five samples of fascicles neighboring an implant and six samples of control tissue from animals in which no implants were placed. The polyLIFEs demonstrated a high degree of biocompatibility, as no adverse effects on axon size were observed in either the implanted fascicle or neighboring neural tissue. However, the insulative cuffs were found to be a source of compression, resulting in necrosis of the neural tissue.

Fabrication and biocompatibility of polypyrrole implants suitable for neural prosthetics

“…One challenge is finding materials that effectively interact with neural tissue for these applications. The stability and biocompatibility of different polymers have been studied by examining their effect on the surrounding tissue after implantation [4][5][6][7][8]. A unique subset of these materials, conducting polymers, has been investigated for use in biomedical applications [9][10][11].…”

A Microchannel Neuroprosthesis for Bladder Control After Spinal Cord Injury in Rat

“…Current designs for peripheral nerve recording interfaces have various issues that have prevented routine clinical use. These include regenerative sieve electrodes (14)(15)(16) that require transection of a peripheral nerve for implantation, invasive penetrative arrays for intracellular recording from dorsal root ganglia (17)(18)(19), and cuff electrodes that wrap around intact sensory nerves and roots (20)(21)(22)(23) but generally produce a poor SNR even with optimal filtering (24). For example, recording of bladder sensory information has been attempted using cuffs in anesthetized humans (21), but the signal size (5 mV, SNR = 0.2) is insufficient for use while awake and moving.…”

Material considerations for peripheral nerve interfacing

“…32 Limitations of the LIFE include drift in the population of cells being recorded and a decrease in signal-to-noise ratio over time. 33 More recent versions of the LIFE have been tested but are not commercially available, including the polymer-based LIFE (poly-LIFE) and the the thin-fi lm LIFE (tf-LIFE). The poly-LIFE is a silicone insulated 12 μ m diameter Kevlar (poly-paraphenylene terephthalamide) fi ber coated with titanium, gold, and platinum over a 1 cm active area.…”

“…34 This electrode has an average impedance of 14.4 k Ω , signal-to-noise ratio of 3.6, single spike amplitudes as high as 120 μ V peak to peak, and background noise of 10-20 μ V, with an average of 30 μ m encapsulation layer thickness. 33 The poly-LIFE was successfully used in the short term to stimulate severed nerves proximally to the stump of subjects with upper limb amputation, where it elicited graded sensations of touch, joint movement, and position. 28 , 35 In turn, the tf-LIFE consists of a fl at ribbon of polyimide 10 μ m thick and 50 mm in length with a Young's modulus of 8.3 GPa, with four 40 μ m diameter circular platinized electrode contacts.…”