Howdy, all,  I just got to play with some of these tiny Nanomuscle
linear activators:  http://www.nanomuscle.com/

Mechanical power appears to be linear and "pneumatic-like" throughout
the entire stroke.  Longer strokes require simple external linkage.
Interesting!  Take out a home loan and try a few.

Specs from the web site:

  Operating voltage: 2.5 to 40+ V
  Operating Current: 80+ mA
  Nominal Force: 30 gf - 70 gf
  Activation Speed: 10 msec - 1 sec
  Stroke: 4 mm
  Ambient Temp: -70 C to +75 C
  Cycle Life: 1 M - 5 M Cycles
  Digital or analog interface.

Cheers.

Pete Woodworth
San Luis Obispo, California