Design and fabrication of neural implant with thick microchannels based on flexible polymeric materials

Abstract

Mechanical guidance can be used to provide a supporting structure through which and onto which regenerating axons can grow. The dimensions of the mechanical guide need to be suitable to support regenerated axon outgrowth and vascularisation. In this paper, we present the design and fabrication process of a three-dimensional (3D) device comprising a bundle of parallel (100 microm x 100 microm) microchannels with embedded electrodes. This device can be used as a 3D electrode interface for peripheral nerve repair. The skeleton of the device is entirely made of flexible polyimide films. Gold microelectrodes and microchannels of photosensitive polyimide are patterned directly on polyimide substrates. After fabrication, the 2D electrode channel array is rolled into a 3D channel bundle that fits the anatomy of the peripheral nerve. Samples are rolled and inserted into 1.5mm inner diameter tube.

Spiral peripheral nerve interface; updated fabrication process of the regenerative implant

“…During the development of the current SPNI device, it was found that, to achieve a reliable ball bond through the connection hole, the photosensitive polyimide (PSPI) substrate layer should be no thicker than 20m. This conflicts with the requirement that the gold wiring layer should be on the neutral plane of the structure to avoid stress on the thin gold film during rolling [7]. Earlier work had suggested that a substrate thickness of 37m should be used.…”

“…By surrounding the regenerated axon with an insulating medium, the axon signals can be increased for neural recording and the amount of current required for stimulation is reduced [6]. The spiral peripheral nerve interface (SPNI) [7] has been developed to provide a microchannel array into which regenerating axons grow [8], where electrodes integrated into the channel cavity are capable of recording from the regenerated tissue. The microchannel array has previously been shown to be capable of recording from, and stimulating, regenerated nervous tissue in vivo [9] [10].…”

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

“…The polyimide contact pads are interfaced with electronic hardware using a commercial connector such as a zif connector. The recording sites are typically 100 9 50 lm 2 9 150 nm gold pads; 20 electrodes per implant are distributed in micro-channels in the third rolled layer where the bending radius is *600 lm [2]. Note that this third rolled layer was selected as it supports the most robust axon outgrowth compared to channels located on the outer roll of the implant [21].…”

An ASIC for Recording and Stimulation in Stacked Microchannel Neural Interfaces

“…MNIs have been manufactured with a range of techniques: silicone casting [23], photopatterning polyimides [20], [29], [30], silicones [28], SU-8 photoresist [25], [31], and laser micromachining [32]. Existing MNI designs use passive conductors (metal thin-films, wires, or foils) to form electrodes and interconnects.…”