An amazing 3D printed project from gifted designer Matthew Borgatti uses pneumatically controlled air chambers to create the spooky, organic behaviors of this design, detailed further in Soft Robots. And check out his posts in the Adafruit Forum as he developed the project! From the video description:
I’ve been developing ways to use 3d powder printing to make air powered robots that have no hard moving parts. Using procedural modeling I can create rapid iterations, incremental designs, and inexpensive prototypes with a simple set of tools. Find more details here.
Here’s an early demonstration of a trefoil tentacle in action. There are three hollow ribbed volumes inside this tentacle that control its motion. It is controlled through a Processing interface and an Arduino switching a bank of solenoid valves using a simple Darlington transistor. You can grab the code here at the Adafruit Forums.