An array of highly flexible electrodes with a tailored configuration locked by gelatin during implantation—initial evaluation in cortex cerebri of awake rats

Abstract

Background: A major challenge in the field of neural interfaces is to overcome the problem of poor stability of neuronal recordings, which impedes long-term studies of individual neurons in the brain. Conceivably, unstable recordings reflect relative movements between electrode and tissue. To address this challenge, we have developed a new ultra-flexible electrode array and evaluated its performance in awake non-restrained animals.Methods:An array of eight separated gold leads (4 × 10 μm), individually flexible in 3D, were cut from a gold sheet using laser milling and insulated with Parylene C. To provide structural support during implantation into rat cortex, the electrode array was embedded in a hard gelatin based material, which dissolves after implantation. Recordings were made during 3 weeks. At termination, the animals were perfused with fixative and frozen to prevent dislocation of the implanted electrodes. A thick slice of brain tissue, with the electrode array still in situ, was made transparent using methyl salicylate to evaluate the conformation of the implanted electrode array.Results: Median noise levels and signal/noise remained relatively stable during the 3 week observation period; 4.3–5.9 μV and 2.8–4.2, respectively. The spike amplitudes were often quite stable within recording sessions and for 15% of recordings where single-units were identified, the highest-SNR unit had an amplitude higher than 150 μV. In addition, high correlations (>0.96) between unit waveforms recorded at different time points were obtained for 58% of the electrode sites. The structure of the electrode array was well preserved 3 weeks after implantation.Conclusions: A new implantable multichannel neural interface, comprising electrodes individually flexible in 3D that retain its architecture and functionality after implantation has been developed. Since the new neural interface design is adaptable, it offers a versatile tool to explore the function of various brain structures.

A Critical Review of Microelectrode Arrays and Strategies for Improving Neural Interfaces

“…The resulting FBR and glial scar formation following implantation of the dextran coated MEAs was shown to be very minimal, with neurons infiltrating the dextran coating site following dissolution (Figure ,H1,H2). In a study by Agorelius et al, flexible MEAs were encased in a hard gelatin coating to aid in penetration, which would dissolve following MEA implantation. It was found that after several weeks following implantation, signals obtained from each MEA remained relatively stable, indicating that the gelatin coating prevented the MEA from becoming damaged during implantation.…”

Mechanical characterization of compliant neural probes, their insertion regimes and a rule of thumb design

“…This formula is often used for compliant probes in the literature [7], [8] where is the mode of buckling, generally taken as 1 unless this mode is artificially restricted, E is the Young's Modulus of the probe's material, I the second moment of area, L the probes length and k the probes effective length. The value for k varies from 0.5 -2 depending on the boundary condition of the probe-tissue contact [9]- [11]. The column effective length factor k captures the degree to which each end of the column is constrained against movement.…”

Microfluidic‐Release Insertion Shuttle Designed for Implanting Flexible Biomedical Electronic Devices into Live Bodies

“…Figure c shows an optical image of the prepared insertion shuttle holding a flexible device (solar microcell array (3 × 6), each size: 600 µm × 800 µm, thickness: ≈4.1 µm) with the aid of a temporary adhesive (thickness: ≈30 µm) that is a mixture of gelatin, glycerin, and water. As gelatin extracted from animal proteins is known to be biocompatible and bioresorbable, it is widely used in drug delivery, medical glues, and hemostatic sponges, as well as coatings for implantable medical electrodes . Glycerin also known to be biocompatible is used as a plasticizer .…”