Saturday, June 16, 2007

Intersections, compilations, trepanations

I thought some might find this useful. Data? Data? We don't need no stinking data!!!! Oh wait. Yes, yes we need data... [taken from Mind Hacks]

Of particular interest is this nice list of available software. What a gold mine!

And Jebus, Medgadget has so many nice posts, maybe I should just auto-mirror their site! Just kidding, but be sure to check out this article on PEDOT, which offers the possibility of highly molded interfacing surfaces for future implants. Keep your eyes on this technology - I would give it an 80% chance that it will work its way into devices within 12 years. (Please note that if you make money on this suggestion, you owe me half, and if you lose money, hey, that's too bad for you!) Conductive polymers rock! Oh lawd, did I really just say that?

And lastly, for a little Friday fun, the Neurophilosopher has an article that is getting lots of attention, and dang nabbit if it isn't really interesting. Remember hearing from random people how The Ancient People of (insert some random place here) performed brain surgery 20 million years ago? Well, he's got the history of trepanation, complete with some wicked pictures, all laid out for you. I promise you will cringe at least one during the read.


Drew said...

Not to be a party pooper, but I am a little skeptical about usability of the conductive polymer. With regard to penetrating implants (ie. intracortical or subcortical) the problem with the immune reaction occurs all along the shaft, not just at the metal contact. Developing new materials for insulating and coating wires is key, but does not seem to be happening soon (in fact, if you look at papers from the 60s and 70s, you will see they coated their electrodes in pretty much the same stuff we use today). While on the subject of insulation, this article does not discuss how these polymers would be insulated. This is key, because much of the recording quality relies on the surface area and shape of your conductive tip. Without insulation, we cannot talk about quality of the recordings. Another problem is introduction into the brain, if the material is like liquid until cured then it is going to have a hard time penetrating the pia (or neural tissue for that matter) unless it is assisted. But, with assistance you introduce damage to the surrounding tissue (although, acute damage clears up within weeks).

Where I see this stuff being really useful is as on-the-spot custom contoured pads for recording directly on the cortical surface.

It would also be neat to see if they could control the degree of stiffness with a magnetic field. A group of materials called ferrogels have this property. You could have it be stiff when driven into the cortex, then soft once it has penetrated. Of course, this defeats the purpose of having it be contoured to the cell bodies around it.

That being said, it does sound neat.

Brandon King said...

Those are some great comments. I still think that conductive polymers would offer some significant benefits, though.

First, as far as immune reaction, greater surface area does generally equal greater gliosis, but that usually caps out about a month or so after implant (there are still reactive astrocytes throughout the life of the implant, but aggregation eventually tops off at a managable level). With conductive polymers you avoid having large surfaces covered in electrode bases. Resting anything over a few centimeters on the cortical surface results in the underlying tissue dying, so having a moldable, multi-layer electrode with a more 'organic' form would allow more freedom in design.

I am kinda putting the cart before the horse, though. What you would need first is an insulating material with similar properties (though not ferrogels if you ever intend to do an MRI). I envisioned a branching insulation that could be solidified on the exposed surface, followed by a conductive polymer inner 'filling'. Something like a non-nano-nanotube. Insertion would be tricky (so tricky that I have no suggestions!), but the flexibility of a smaller pial tear resulting in more lateral areas to insertion would seem to be beneficial as far as minimizing insertion/acute damage.

It is an interesting material because of the flexibility, and a difficult one to apply for the same reason. I'm not a materials scientist, but I would suspect there are at least a few labs looking at neural electrode applications, and working through all these issues. Maybe I'm being a little optimistic on the timeframe, though. Neat stuff.

Drew said...

I agree with everything you said Brandon. Periodically there are papers in either Nature or Science on self-assembling circuits and insulators. Of course, these assemble under very specific conditions but it is promising nonetheless. My philosophy with regards to methods in science is that the best ones use the intrinsic properties of the material to solve the problem, such as immunostaining or blocking protein expression with RNAi. People like methods that do not require them to do much heavy lifting.

As for this polymer, where this might find good use is with cortical recording from "floating" microelectrodes. Flexible conductors would be great for this application since they would move with the brain.

Brandon King said...

I agree. I find self-assembly, whether in materials or robotics/comp sci extremely interesting. I think the first step is actually figuring out the rules governing the methid of assembly. After that, the material it acts on seems to be less of an issue. Sure there will be exceptions and special cases, but once the rules are worked out, there are enough smart people out there to figure out ways of applying them to other materials/algorithms.

IConrad said...

Regarding the development of scar tissue in neural substrates: Rutledge Ellis-Behnke at MIT has an answer to this problem. Regarding insulation: while not necessarily directly applicable to this situation as-yet (due to the rigidity of the structures), IBM's work with self-assembling vacuum nanoscale "air-pocket" insulation for microchips might just have its uses here as well.

Combine all of this with "WiTricity" and what you essentially get is a means by which we can successfully bypass most-all of the ethical constraints preventing the wholesale development of neural augmentation implant technologies.

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