Mechanochemical actuators

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Abstract
There are synthetic polymers which can exert a force and mechanical work by contracting themselves in the presence of chemical solutions. They can convert chemical energy directly into mechanical energy, similar to biological (skeletal) muscles. Hence, these synthetic polymers are called mechanochemical systems, mechanochemical actuators, or artificial muscles. Mechanochemical actuators can be obtained with rubber, collagen, and polyelectrolyte gels. This paper surveys the mechanisms of contraction and swelling, the mechanical properties, and several applications of mechanochemical actuators. The mechanochemical engine driven by contractile collagen fibres, which was originally developed by A. Katchalsky and recently examined by some workers in Japan, is also reported. The mechanical properties of polyelectrolyte gels (cross-linked polyacrylic acid and ion-exchange resins, and a mechanochemical piston packed with the resins) are discussed. Mechanochemical actuators of polyelectrolytes can be activated by electric stimulation, and the experimental method and results are presented. Several manufacturing processes for applications of mechanochemical actuators to industrial purposes and robot actuators have also been treated. Several examples of the treatments and experimental results are presented.