A simple implantation method for flexible, multisite microelectrodes into rat brains

Abstract

A long term functional and reliable coupling between neural tissue and implanted microelectrodes is the key issue in acquiring neural electrophysiological signals or therapeutically excite neural tissue. The currently often used rigid micro-electrodes are thought to cause a severe foreign body reaction resulting in a thick glial scar and consequently a poor tissue-electrode coupling in the chronic phase. We hypothesize, that this adverse effect might be remedied by probes compliant to the soft brain tissue, i.e., replacing rigid electrodes by flexible ones. Unfortunately, this flexibility comes at the price of a low stiffness, which makes targeted low trauma implantation very challenging. In this study, we demonstrate an adaptable and simple method to implant extremely flexible microprobes even to deep areas of rat's brain. Implantation of flexible probes is achieved by rod supported stereotactic insertion fostered by a hydrogel (2% agarose in PBS) cushion on the exposed skull. We were thus able to implant very flexible micro-probes in 70 rats as deep as the rodent's subthalamic nucleus. This work describes in detail the procedures and steps needed for minimal invasive, but reliable implantation of flexible probes.

Smaller, softer, lower-impedance electrodes for human neuroprosthesis: a pragmatic approach

“…Indeed, even state-of-the-art rigid microelectrodes cause severe mechanical trauma during their insertion, resulting in a thick glial scar formation and a consequent loss of tissue-electrode coupling as time goes by (Turner et al, 1999; Polikov et al, 2005; Leach et al, 2010; Richter et al, 2013). That being said, (Krüger et al, 2010) did manage to achieve stable recordings for several years from electrodes experimentally implanted in monkeys thanks to the minimal invasiveness of their device at the cortical recording site.…”

Microfluidic drive for flexible brain implants

“…However, the implantation of flexible probes itself is a matter of concern, as removable implantation aids [15,23] increase the surgical footprint, thus potentially nullifying the flexible probes' advantages.…”

“…Probes with increased thickness and width can easily withstand higher forces during insertion, but this in turn is expected to cause a stronger tissue response [5]. The use of insertion aids for flexible probes increases tissue damage, limiting the advantages of flexible electrodes [15]. We propose in the following the use of a microfluidic device to provide the necessary forces for pial penetration of flexible probes by means of fluid forces.…”

Feasibility Study of High-Performance Implantable Stimulation Electrode with Nanocomposite Gel Coating as a Brain–Machine Interface Device

“…However, the hydrogels that are as soft as the tissue present difficulties during implantation. (8) In order to address this issue, we propose the hydrogel-coated electrode using a nanocomposite (NC) gel with high mechanical property as the coating material. The objective of this study is to confirm the feasibility of improving the performance of implantable stimulation electrodes by coating their surfaces with the NC gel and to clarify the characteristics of the stimulation electrode with the NC gel coating in vitro.…”