Electrode Bundle Fabrication

Proposal Demonstration for Paradromics

Quick Look

Problem: The microwires of an electrode needs to be small and thin to prevent tissue damage. However, a thinner wire is more prone to bending, which makes placement of the electrodes less accurate

Proposal: Instead of polishing the ends of the microwires to make them sharp, an alternative can be pulling the wires while heating until it naturally pulls apart at a point.

Detailed

The microwires of the electrodes needs to be able to penetrate the tissue in order to measure accurate

Wires with diameters of 15–20 μm has shown to cause minimal damage to the blood brain barrier

However, small wires can buckle, so the wires do not follow a straight line. As a result, placement of the electrodes can be inaccurate.

A method of fabricating the wires is using 20 μm wires and polishing them down to form a 30° sharp edges.

I propose creating a tapered profile, so that the diameter of the wire decreases to a sharp point. The benefits of this wire can be seen in that math. “The critical buckling force decreases with the fourth power of the radius”, so if the radius increase linearly then the critical buckling force will increase exponentially. As a result, buckling will not occur but the diameter of the wire will still be sharp.

This can be accomplished by slowly pulling the wires as a section of it gets heated. Pulling the wires will naturally decrease the diameter, until the diameter gets so small that it pulls apart - creating a needle point. By controlling the rate of pulling and rate of heating, this can allow for new and repeatable wire geometry.

Citation

This problem and proposal was inspired by the article CHIME: CMOS-Hosted in vivo Microelectrodes for Massively Scalable Neuronal Recordings.

The solution was also inspired by thermal drawing and my observation as I was making hand pulled noodles.