Advanced Prosthetics: Challenges of Creating Brain-Controlled Limbs

[Universe_Man]

What are some of the obstacles faced in creating prosthetic limbs that are actually controlled by your brain, just like your real limbs are? I always thought how interesting it would be to actually have a artificial limb that works just like, or better than a biological limb. Do we not know enough about how the brain controls muscles to properly emulate it?

 

[Danger]

Hi, UM. While I used to be into this very heavily, I haven't really followed the subject in over 20 years. Obviously, my knowledge will be outdated by technology to some extent. Still, most of the basics are probably pretty much the same.
To start with, muscles are extremely well adapted for what they do. Replicating the smooth, proportional motion of flexing a finger (and each joint individually, at that) with a motor, hydraulics, pneumatics, or shape-memory metal is hard enough to start with. To do it with anything like the force that muscles exert, and keep it all in a package that is no larger than a real arm, is just about impossible. And other than using an isotope power source, I can't think of any current battery technology that would keep the thing running for any appreciable length of time. I seem to recall seeing something somewhere about an artificial muscle (might have been in the Engineering section right here in PF) that could potentially solve that.
There are two main 'brain control' systems. The one that is commonly used is called 'myoelectric'. It uses skin contact electrodes to detect the electrical activity of a muscle in the intact part of a limb. The signal is then amplified and used as the control for the powered artificial part. This means, of course, that the wearer has to learn a new set of muscle commands to achieve the desired result. The other system is 'neuroelectric', wherein an electrical contact is actually introduced into a nerve fibre. That has apparently come along a lot since my day. Some (at least experimental) set-ups even have the electrodes implanted in the motor cortex of the brain. Once the signal is picked up, the rest is the same as in a myoelectric system. One of the advantages is that the wearer has only to do the same thing that he/she would if the original limb was intact.
One of the major hurdles to 'realistic' or 'natural' action of a prosthesis is feel. On-board electronics compare the action of the limb with the intent of the wearer. The force and velocity of a hand closing, for instance, is regulated by the muscle or nerve impulse so you can pick up something heavy, but still handle an egg without breaking it. Unfortunately, those feedback signals, as far as I know, can't be realistically relayed to the wearer. If you've ever tried to write, or even pick up a glass, when your hand is 'asleep' or very cold, you know that it isn't all that easy.
There are probably others here who know a lot more about it than I do, so I hope a few come on board. Meanwhile, you might try looking on line for more information. I'd start with the Utah State University (I'm not sure that's the exact name; maybe University of Utah?). They were always the leading edge researchers in prosthetics.

 

[Danger]

Ha! I found it.
Quite by accident, I admit. I was looking for something else. Anyhow, here it is. http://www.scienceagogo.com/news/20060216225242data_trunc_sys.shtml"

 

[Universe_Man]

Wow, I found that really interesting. Thanks for helping me out, Danger.

 

[Danger]

Any time, dude.
It's nice to see that people are still interested in this field. There are an awful lot of people out there who need this kind of technology, and yet this is the first time that I've seen anyone in PF express curiosity about it. I know that the talent and expertise exist right here, so I really hope that others get involved. Back in the day, I actually designed the things, but my education is severely lacking as far as electronics and servo mechanisms goes. There weren't any IC's back then, so the most technical things involved were force clamps, velocity clamps, and Schmitt triggers (probably spelled that wrong). I certainly hope that you're considering this as a line of work; the world needs people who can do it. Please stay in touch.

 

[Danger]

In the Engineering section, DigEagle just posted a link to a neat set of videos directly addressing this subject. #3 is about smart prosthetics, and #4 about the artificial muscle. Here it is:
http://www.techreview.com/player/video/video_compact_leader.aspx?id=44164231&autoplay=true

 

[Universe_Man]

Any time, dude.
It's nice to see that people are still interested in this field. There are an awful lot of people out there who need this kind of technology, and yet this is the first time that I've seen anyone in PF express curiosity about it. I know that the talent and expertise exist right here, so I really hope that others get involved. Back in the day, I actually designed the things, but my education is severely lacking as far as electronics and servo mechanisms goes. There weren't any IC's back then, so the most technical things involved were force clamps, velocity clamps, and Schmitt triggers (probably spelled that wrong). I certainly hope that you're considering this as a line of work; the world needs people who can do it. Please stay in touch.

Hey there Danger,

Ha ha, I remember this thread! I think I made it when I was a Junior in High School! I'm almost into my third year of college now, with a major in Material science and engineering. I'm still fascinated by prosthetic technology, and it's one of the things I want to get into! What I'm aiming for with a Material Science degree is to do research in artificial muscles, and perhaps other things that will make prosthetics more lifelike (power sources, etc).

Here's some interesting videos I have found on Youtube about some prosthetic test subjects (one of my favorite guys is Jesse Sullivan, he's in the first three videos).



http://www.youtube.com/watch?v=T6R5bm6qx2E&feature=related
http://www.youtube.com/watch?v=6rloSSqiUCM&feature=related

I hope to go to grad school after I get my B.S, and be able to do some research somewhere. Right now, I'm reading about biomechanics, and how real muscles work, which I think will be important in simulating them.

It's good to talk to you again! I'll send you a PM with my email, feel free to contact any time!

 

[Danger]

You old necroposter! Great to hear from you. Those videos go far beyond anything that I had envisioned as currently possible. Thank you so much for reviving this thread. E-mail is on the way.