Stable, long-term single-neuronal recording from the rat spinal cord with flexible carbon nanotube fiber electrodes

Abstract

Objective. Flexible implantable electrodes enable months-long stable recording of single-unit signals from rat brains. Despite extensive efforts in the development of flexible probes for brain recording, thus far there are no conclusions on their application in long-term single neuronal recording from the spinal cord which is more mechanically active. To this end, we realized the chronic recording of single-unit signals from the spinal cord of freely-moving rats using flexible carbon nanotube fiber (CNTF) electrodes. Approach. We developed flexible CNTF electrodes for intraspinal recording. Continuous in vivo impedance monitoring and histology studies were conducted to explore the critical factors determining the longevity of the recording, as well as to illustrate the evolution of the electrode–tissue interface. Gait analysis were performed to evaluate the biosafety of the chronic intraspinal implantation of the CNTF electrodes. Main results. By increasing the insulation thickness of the CNTF electrodes, single-unit signals were continuously recorded from the spinal cord of freely-moving rats without electrode repositioning for 3–4 months. Single neuronal and local field potential activities in response to somatic mechanical stimulation were successfully recorded from the spinal dorsal horns. Histological data demonstrated the ability of the CNTF microelectrodes to form an improved intraspinal interfaces with greatly reduced gliosis compared to their stiff metal counterparts. Continuous impedance monitoring suggested that the longevity of the intraspinal recording with CNTF electrodes was determined by the insulation durability. Gait analysis showed that the chronic presence of the CNTF electrodes caused no noticeable locomotor deficits in rats. Significance. It was found that the chronic recording from the spinal cord faces more stringent requirements on the electrode structural durability than recording from the brain. The stable, long-term intraspinal recording provides unique capabilities for studying the physiological functions of the spinal cord relating to motor, sensation, and autonomic control in both health and disease.

Challenges and Opportunities of Implantable Neural Interfaces: From Material, Electrochemical and Biological Perspectives

“…Simultaneously, there was no evident alteration in the structure and no signal degradation at the stimulation sites after implantation for 6 weeks, implying excellent chronic biocompatibility and stability. Liu et al [139] applied flexible CNTF electrode on intraspinal recording of freely-moving rats, demonstrating that CNTF microelectrodes greatly reduced the gliosis compared to the stiff metal electrodes and that single-unit signals could be recorded continuously without electrode repositioning for 3-4 months by increasing the insulation thickness. The bending stiffness per width was ≈4.2 × 10 3 nN m, much smaller than silicon probes (4.6 × 10 5 nN m), but still higher than those of neural tissues (<1 nN m).…”

Lifetime engineering of bioelectronic implants with mechanically reliable thin film encapsulations

“…Alternatives to metal microwires have been explored, most notably carbon fiber microelectrodes (figure 1(B)). While similar in elastic modulus to some metals, carbon fiber electrodes deform more elastically than metal microwires, and are capable of returning to their original shape after thousands of cycles of deformation without significant material fatigue [93], an advantageous property in more mobile implant locations such as the spinal cord, which can experience up to 10%-20% tensile strain during normal movement [94]. Carbon fiber electrodes have also demonstrated relatively enhanced durability, conductivity, and resistance to corrosion [95,96], making them a promising material for the continued development of devices in the microwire family.…”

“…Median lifespans for rigid and flexible substrates were found to be 216 and 108.5 d respectively. Ninety seven studies were included in the analysis, for which the supporting data can be found in supplementary data table 2 [12,17,30,90,94,96,97,101,114,115,121,131,136,142,153,168,170,223,241,242,244,331,379,389,390,393,394,.…”

Ultraflexible electrodes for recording neural activity in the mouse spinal cord during motor behavior

“… 17 – 20 As a result, electrophysiological recordings in the spinal cord are mostly restricted to ex vivo , 21 , 22 anesthetized, 23 – 26 or acute preparations. 27 Even in the impressive but few examples of spinal recordings in awake-behaving contexts, animals were highly constrained, 28 – 33 motor activity was tightly circumscribed (e.g., isometric contractions of wrist muscles), 28 , 29 , 31 , 32 and/or neurons were recorded one at a time 30 , 34 , 35 or for short time periods. 30 , 34 Importantly, because the spinal cord mediates whole-body motor behaviors, a deeper understanding of spinal circuits requires unrestrained recording during precisely those actions that drive the most severe displacements of tissue.…”