Project #33: 3D Print Soft Robotics with PVA Molds filled with Silicone

Lately there has been a lot of interest in soft robotics. These tend to use pneumatics or hydraulics in fluid-tight chambers which change shape based on pressure.

It is not easy to 3D print with flexible air-tight material. I have done it by using Ninja Flex and then treating it heavily with Methyl Ethyl Ketone (MEK). Better would be to use silicone poured into a mold. However, how do you make something like a “pipe” that or a “artery”?

This is somewhat difficult to cast. Of course you can purchase hoses, but then if you have many chambers you have a complicated manufacturing project. Instead, we should 3D print in PVA (polyviny alcohol), which can now be readily purchased in filament for a 3D printer, to make a complicated mold. I’ve used it to make dissolvable support structures. It works, but is finicky.

PVA dissolves in water. So we can use the “lost wax” method. We 3D print the mold, fill it with silicone, use room-temperature vulcanization to harden it, and then dissolve away the PVA.

Could we in this way make an accurate silicon model of a heart, complete with functional valves and chambers? (I’m assuming the muscle would not be a part of this process; that would be the next step.)

In this way would could make a silicone structure (such as the octet-truss) filled with a fluid and inject resistivity or pressure sensors to understand the deformation of the structure under stress. Alternatively, if you control the flow of air or water into they structure, you could make a soft robot component in this way.

I’m a little busy getting the gait working for the Austin Maker Faire; can somebody please try this out and report on it? A simple first project would be to make fluid-filled silicone torus.