engineering references:control, power and actuators

A robot must be able to interact physically with the environment in which it is operating. The key difference between a robot and a ‘‘softbot’’ or software agent lies primarily in a robot’s having actuators that permit it to affect the environment, say, by exerting forces upon it or moving through it, which a softbot lacks. Some of the most common actuators are artificial muscles of various types, none of which are very good approximations of living muscles; electric motors, the most common actuators in mobile robots, used both to provide locomotion by powering wheels or legs, and for manipulation by actuating robot arms (special-purpose motors, such as stepper motors, are used for precision movement); pneumatic and hydraulic actuators, used in industry for large manipulation tasks, but seldom for mobile robots. (from: https://mitpress.mit.edu/sites/default/files/titles/content/9780262025782_sch_0001.pdf)

Soft actuators bring both power and natural fluidity to robots. These actuators offer high power to weight ratio in conjunction with compliance, enabling robots to carefully apply high forces to their environments. Additionally, compliance offers inherent adaptability and forgiveness, desirable characteristics in uncertain and dynamic environments.
Construction and operation of soft pneumatic actuators are relatively simple and robust. The actuators are made of elastomer films with embedded fluidic channels and operate by the expansion of these compliant channels under pressure - more in article: Soft Robot Actuators using Energy-Efficient Valves Controlled by Electropermanent Magnets

 

Compliant Robotics and Automation with Flexible Fluidic Actuators and Inflatable Structures

A 450-mAh, 3.7-V battery will keep it swimming along at 1.1 centimeters per second for a solid 3 hours and 15 minutes, and it can even carry a tiny camera. Maximum untethered speed is 6.4 cm/s, and the robot fish will happily swim around in water temperatures ranging from slightly above freezing to nearly 75° C. - more on link
and literature:

electroactive polymers

Electro active polymers convert electrical energy directly into mechanical work. An elastic membrane made of polymer material is made to deform by subjecting it to an electric field, and when the voltage is removed the membrane regains its original size and shape. Both sides a polymer film is given a very thin coating of electrically conductive graphite, to which the voltage is applied, the device then acting as a compliant electrical capacitor. The electrostatic forces cause the surfaces of the membrane to draw together, compressing the material and causing its surface area to increase. (from link)
Actuator design with internal reinforcement (on link)

Electroactive-Polymer Actuators for Controlling Space Inflatable Structures

The electrostatic interactions between the two sides of the self-propelled spheres could be manipulated by subjecting the colloids to an electric field. Some experienced stronger repulsions between their forward-facing sides, while others went through the opposite. Along with them, another set remained completely neutral. This imbalance caused the self-propelled particles to swim and self-organize into one of the following patterns, which are swarms, chains, clusters and isotropic gases.
To avoid head-to-head collisions, head-repulsive particles swam side-by-side, forming into swarms. Depending on the electric-field frequency, tail-repulsive particles positioned their tails apart, thus encouraging them to face each other to form jammed clusters of high local density. Also, swimmers with equal-and-opposite charges attracted one another into connected chains.
Dr. Granick states, "This truly is a joint work of the technological know-how by the Korean IBS and the University of Illinois, as well as the computer simulations technology by Northwestern University." He expects that this breakthrough has probable application in sensing, drug delivery, or even microrobotics.
With this discovery, a drug could be placed within particles, for instance, that cluster into the delivery spot. Moreover, alterations in the environment could be perceived if the system unexpectedly switches from swarming to forming chains (from link).
Read more at: https://phys.org/news/2016-07-self-organizing-smart-materials-mimic-swarm.html#jCp

more literature
Design, fabrication andcontrol of soft robots
Integration of Smart Materials into Dynamics and Control ofInflatable Space Structures
Review of State of Art of Smart Structures and Integrated Systems