Electromechanical Muscle?

Mateorabi asks: "We just saw in a previous Slashdot article on how advances are being made in converting between electrical energy and torque motions. Does any sort of material have similar properties for contraction/expansion motions? I have in mind something like a plastic that would contract a good distance under an applied voltage: similar to the properties of human muscle tissue in behavior and strength. Wouldn't such a be a perfect for use in artficial limbs (+ lots of other stuff too)?"

Making it perfect for use?

[Lord_Hern]

All materials that are currently examined for contractile action to applied current suffer from a fundamental flaw - fatigue failure. Materials are engineered to withstand X load under Y cirumstances with Z tolerance for T time. Exceed that and the device will fail catastrophically.
Living tissues actively repair themselves when wearing out. As long as the tissue isn't completely destroyed it will recover.

1. The real question is: How can a contractile material be developed to withstand and
2. recover from fatigue related failures similar to a muscle?

Nitinol

[Matt_Bennett]

There is a metal called Nitinol, which is known as a shape memory alloy, commonly known as "muscle wires" that contract when heated. They are also low resistance conductors, so they will contract when you put current through them (and heat them up). Here's some more information. [robotstore.com] They call it "Flexinol" though. You can get small actuators, but it has limitations in that these muscles are slow, and can only "pull", they must cool down to go to their extended state, which can take some time. Also, they require a lot of current (at low voltages).

I have seen some work done with pneumatic bladders in a mesh sleeve, when they are inflated, the sleeve causes the pneumatic muscle to contract. It is called a "McKibben Actuator", here's some more information [prairienet.org].

Re:Nitinol

[iplayfast]

I've played with the "muscle wires", they are not slow compared to normal muscles. They also cool down quite quickly. The biggest problem is the amount of power they require, (in order to heat up). The second biggest problem is that they are hard to work with. You can't solder them, you have to crimp them. Still is very neat if power is no problem.

Artificual Muscles

[maggard]

Well, here's a report on plastic muscles being developed for extra-terrestrial robots:

http://www.robotbooks.com/plastic-muscles.htm [robotbooks.com]

I also recall sering a news report on artificial muscles consisting of plastic filaments bunched together expanding and contracting in response to PH changes in a fluid bathing them. Unfortunately this also brought back memories of an awful Farah Fawcett sf film and I promptly blocked all detailed recollection.

Trade Show

[Lede Singer]

Though I am not a big fan of trade show prices, if you are serious, then I'd suggest getting ahold of some publications or trade show info on polymers. Web sites such as Society of Plastics Engineers [4spe.org] and Ge Polymerland [gepolymerland.com] are helpful, but what I would recommend is for you to attend ANTEC 2001 [4spe.org]. This trade show will have all of the new polymer technologies, not just in fillers or money savers, but also (and probably more-so) in engineering plastics for cel phones, medical, automotive, and many, many other areas. I don't think that I am going to attend because I have no real reason to, but if I was wanting to design an artificial limb, I'd be there.

If you want any more plastic links, I have quite a few.