  Solid state actuators (piezoelectric, ferroelectric, ...) deform under an
external field, and have found many applications. They respond fast, but their
mechanical deformations are very small. There is a need for soft actuators,
giving larger responses, but necessarily less fast. This paper describes the
early attempts by Katchalsky and others, and the problems which showed up
-related to time constants, and, most importantly, to fatigue. Two current
attempts are reviewed.
