Knowledge Base

The Polyethylene Glycol (PEG) provide temporary support for the whole microwire array. Without this support or if the support part is too short, all the long wires will squeeze together and it will be very difficult or even impossible for the wires to penetrate and advance into the brain which very likely will lead to failure of implantation. 

Good thing about PEG is that it can be easily resolved in or washed off by saline. After the tip part of the array penetrates into brain tissue (dura must be peeled off first), the user can use a syringe with saline pointing at the PEG part and gently wash off the PEG, then the covered wires will be exposed. The user then can advance the array further until reaching the desired location/depth. 

Nichrome wires are made of nickel chromium. Typically Nichrome has higher resistivity than tungsten. Tungsten has higher hardness than nichrome.

Due to these differences, we have found the the tungsten MWA can penetrate the pia mater very easily and advance very smoothly while inside the brain tissue. This usually results in immediate beautiful multi-units spikes in many channels. However, the drawback of tungsten MWA is that the multi-units signals usually last only about 2-4 weeks before becoming noisy. Generally, tungsten MWA is good for acute recording or short-term recording.

On the contrary, nichrome wires are a little bit softer than tungsten wires. But with the PEG supporting part, the nichrome MWA can be inserted and advanced in the brain with no problem. And with well practiced surgical techniques, the multi-units signals from nichrome MWA can last several months with no attenuation. Thus nichrome MWA is optimal for long-term chronic recording which lasts for a couple of months or even longer.