Because vanadium dioxide experiences a sudden phase change at 67° C, instead of trying to make small changes to gradually contract or expand muscles, could an alien instead have many smaller muscles, like a bunch of separate smaller muscles connected to the bone, each one is a little weaker than the one above it, and the placement on the bone makes it so that certain ones can't put very much force into moving the arm.

I imagine that this would make their movement fairly robotic, as to move the arm to a specific spot a certain number of muscles would be heated, contract, and then the arm would suddenly snap to a position. The more muscles activated the stronger the pull kind of thing. Is this more plausible than having one larger muscle?

(If you have any questions I'll do my best to answer them.)

  • $\begingroup$ I know that the phase change is a 10000:1 difference in electrical conductivity, and that it changes the crystal structure, do you have any evidence that you could point to that it would serve as an actuator, I found nothing in a quick search. This is also pretty technical chemical or physical change, you might get better answers starting in chemistry or physics for possible use as an actuator / solenoid resulting from the phase change. $\endgroup$ Commented Aug 23, 2017 at 6:49
  • $\begingroup$ This and the previous VO2 question show a basic misunderstanding. There is nothing "sudden" in a phase change. Think of freezing water or melting ice: the phase change happens at 0 degrees centigrade, but it's not "sudden". Once you bring the ice at 0 °C it won't melt "suddenly" -- it has to absorb the heat of solidification; water doesn't freeze as soon as it reaches 0 °C -- it has to shed the heat of solidification. All phase changes of all materials have an associated specific latent heat which must be exchanged for the phase change to occur. $\endgroup$
    – AlexP
    Commented Aug 23, 2017 at 7:28
  • 5
    $\begingroup$ Possible duplicate of Internal micro-heating and Vanadium Dioxide muscles $\endgroup$
    – sphennings
    Commented Aug 23, 2017 at 11:26
  • $\begingroup$ Finer control? Probably not, given that human muscles are able to perform microsurgery so precise the surgeons need microscopes to see what they're doing. Exactly how fine do you want this control? $\endgroup$
    – Azuaron
    Commented Sep 5, 2017 at 13:08

2 Answers 2


You "just" need to mimic our real muscles.

They are composed of a very high number of "fascicles" which are, composed of many "fibers", composed of muscle cells.

Muscle cells contain a pile of active elements ("sarcomeres") which are the ones actually contracting.

"Recruitement" (proper word to mean: "give to a fiber order to contract") is gradual with certain fibers being "more prompt" to respond than others (full story is more complex, I'm simplifying), so varying the amount of stimulation you end up with a different amount of fibers recruited, and thus a different force applied.

What you need to do with your artificial muscles is to mimic the same structure, with VO2 elements taking the place of sarcomeres, not of the whole muscle.

You can simulate recruitement by electrical stimulation of single fibers as I suggested in the answer to your other question.

This will give you all control you need and will also be easier to justify biologically.


The real problem with using multiple small "muscles" is that they are activated to contract by a temperature change. If you have multiple small fibers it will be very difficult to thermally isolate them from one another if they are close to each other.

In other words you have 2 fibers next to each other, some biological process is used to heat one up to contract that muscle, but the heat will bleed over to adjacent fibers making them also contract. This is not a problem if all the fibers are moving the same way (like individual human muscle cells in a muscle fiber) more heat will trigger more fibers making a stronger pull; but this would be very bad if you had multiple muscle tissues controlling separate movements next to each other. This would make fine motor control with multiple close muscle groups (like in a hand) very difficult.

In order to work best the individual muscle groups will have to be quite distinct and thermally isolated from the other muscles. The easiest way to do that is to not have them be next to each other to minimize the heat transfer. Other more exotic thermal control solutions may of course be possible.


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