Towards artificial muscles
  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. 
Pierre-Gilles de Gennes