A soft and stretchable bilayer electrode array with independent functional layers for the next generation of brain machine interfaces

Abstract

Objective. Brain-Machine Interfaces (BMIs) hold great promises for advancing neuroprosthetics, robotics, and for providing treatment options for severe neurological diseases. The objective of this work is the development and in vivo evaluation of electrodes for BMIs that meet the needs to record brain activity at sub-millimeter resolution over a large area of the cortex while being soft and electromechanically robust (i.e. stretchable). Approach. Current electrodes require a trade-off between high spatiotemporal resolution and cortical coverage area. To address the needs for simultaneous high resolution and large cortical coverage, the prototype electrode array developed in this study employs a novel bilayer routing of soft and stretchable lead wires from the recording sites on the surface of the brain (electrocorticography, ECoG) to the data acquisition system. Main results. To validate the recording characteristics, the array was implanted in healthy felines for up to 5 months. Neural signals recorded from both layers of the device showed elevated mid-frequency structures typical of local field potential (LFP) signals that were stable in amplitude over implant duration, and also exhibited consistent frequency-dependent modulation after anesthesia induction by Telazol. Significance. The successful development of a soft and stretchable large-area, high resolution micro ECoG electrode array (lahrμECoG) is an important step to meet the neurotechnological needs of advanced BMI applications.

A Microclip Peripheral Nerve Interface (μcPNI) for Bioelectronic Interfacing with Small Nerves

“…The μcPNI consists of three components: 1) a sMEA (Figure 1a–c ), 2) a microclip (Figure 1a,c ), and 3) a printed circuit board (PCB) (Figure 1c ). The sMEA has six electrodes, three on Layer 1 (L1) and three on Layer 2 (L2) [ 83 ] to maximize electrode density and reduce the overall dimensions of the device without compromising yield. To secure the electrode on the nerve, we developed the microclip, a 3D printed mechanical nerve anchor using resonant Direct‐Laser‐Write (rDLW) technology that rapidly structures a biostable photoresist (IP‐Dip) with ≈1 µm minimum feature sizes.…”

“…To create the mechanically stable yet elastic electrode array of the μcPNI, we developed the fabrication procedure schematized in Figure 2 a (see Experimental Section). The bi‐layer sMEA consists of 5 layers: 1) the PDMS substrate (45 µm), 2) the microcracked gold [ 84 , 85 ] electrodes of L1, 3) the PDMS encapsulation of the electrodes on L1 (30 µm), 4) the microcracked gold [ 83 ] electrodes of L2, and 5) the PDMS encapsulation of the electrodes on L2 (30 µm) (Figure S1 , Supporting Information). The recording sites of the electrodes (80 µm diameter) are connected via electrode leads (width: 100–380 µm) to the contact pads (width: 650 µm) of the PCB.…”

“…The section of the sMEA with the contact pads (proximal section) was compression‐bonded between two custom PCBs [ 83 , 117 ] with a 16‐channel Omnetics connector (A79040‐001) (Figure 1c ; see Supporting Information for details).…”

“…All tested and imaged devices were fabricated using a custom rDLW system. [79] Printed Circuit Board Assembly: The section of the sMEA with the contact pads (proximal section) was compression-bonded between two custom PCBs [83,117] with a 16-channel Omnetics connector (A79040-001) (Figure 1c; see Supporting Information for details).…”

“…Fabrication of Microelectrode Arrays: The fabrication of bi-layer sMEAs of the 𝜇cPNI builds and extends on previously described methods [83,93,95,115,116] (Figure 2a; see Supporting Information for de-tails). Briefly, the microcracked gold film for the L1 electrodes was deposited by sequential thermal evaporation of 3 nm Cr, 35 nm Au, and 3 nm Cr thickness through a shadow mask on a 45 μm thick PDMS membrane on a glass carrier.…”