Soft Silicone Pneumatics Are 3D-printed In A Tub Of Gel

We’ve seen our fair share of soft silicone robots around here. Typically they are produced through a casting process, where molds are printed and then filled with liquid silicone to form the robot parts. These parts are subsequently removed from the molds and made to wiggle, grip, and swim through the use of pneumatic or hydraulic pumps and valves. MIT’s Self-Assembly Lab has found a way to print the parts directly instead, by extruding silicone, layer by layer, into a gel-filled tank.

The Self-Assembly Lab’s site is unfortunately light on details, but there is a related academic paper (behind a paywall, alas) that documents the process. From the abstract, it seems the printing process is intended for more general purpose printing needs, and is able to print any “photo or chemically cured” material, including two-part mixtures. Additionally, because of the gel-filled tank, the material need not be deposited in flat layers like a traditional 3D-printer. More interesting shapes and material properties could be created by using the full 3d-volume to do 3D extrusion paths.

To see some of the creative shapes and mechanisms developed by MIT using this process, check out the two aesthetically pleasing videos of pulsating soft white silicone shapes after the break.

Other soft robots we’ve seen have included this silicone robotic armopen source soft robotics, and these soft robotic jellyfish.

28 thoughts on “Soft Silicone Pneumatics Are 3D-printed In A Tub Of Gel

    1. Looks like the gel has to be thick enough to support your printing fluid (maybe be the same density) and it has to self heal behind the printing injector (so no jello). The fluid would also have to allow the printing fluid to cure, I’m not sure if silicone caulking will cure when completely submerged. Otherwise its just a long syringe that extrudes liquid rather than filament.

      1. The other interesting observation they made – not just needing the printing fluid to cure but also to not react with the substrate (as they had with some materials which off-gassed CO2).
        I wonder how well a basic agar agar type gel might work.

    1. It’s super cool. I want to play with the three-cell one in the first video which lets you control the position of the end in three dimensions.There’s so much stuff you could do with a printer like this. Custom fleshlight or dildo? Bam it’s done, and you didn’t even have to make eye contact with the cashier at the sex store.

      Gotta love this extremely loud clipping audio on some noname video player that doesn’t have volume or mute controls. Can’t even scrub the video to get a better look at these amazing creations. Where did this garbage video player come from? Why are they using it when there are other free alternatives that actually have features and don’t suck ass? I’m so baffled as to why I see video players without basic scrubbing or volume controls. At least it doesn’t autoplay.

    1. Granular gel.
      The suspension medium is a granular gel, similar in consistency to hair gel or hand sanitizer. It is produced by using carbomer 940, a crosslinked polyacrylic acid polymer in the form of white powder. The carbomer is mixed into water until it is fully dissolved. At this point, a 0.5% (w/v) carbomer-water mixture typically has a pH value around 4.0.
      Next, a neutralizing agent, such as a sodium hydroxide solution, is added until the mixture reaches a pH value of 7.0.
      The carbomer-water mixture transforms into a thick gel as it approaches a neutral pH, with an ideal gelling range between 6.0 and 9.0 for a 0.5% (w/v) carbomer mixture. 17 This exact range varies depending on how much carbomer is added, with a smaller range for less carbomer and a wider range for more. To maintain consistency in our experiments, we always mix our gel to a pH of 7.0.

  1. This is an interesting idea. You can imagine doing almost-conventional FDM in a medium in which the filament was neutrally (or slightly positively) buoyant to obviate the need for support.
    I suspect that the turbulence in the medium cased by the head flying about would require the surface of the fluid to be kept just above the tip of the extruder nozzle.

    1. As they did it, it’s a pre-filled container of support fluid and a needle extruder. However, this could also be done by filling the container incrementally as layers are printed. In this case, taller objects could be made without having to use a very long needle, and this might also make it possible to use simpler fluids.

        1. Yes. Introducing about 200° hot molten plastic in a water based gel will produce steam, but probably no usable print. At least the gel must be compatible with the high temperatures.

  2. Great stuff. The gel is something you can buy on eBay and make yourself with very basic tools (carbomer 940 powder, water and sodium hydroxide). All you need is a 3d printer with a modified extruder (if you use UV resin it’s even simpler than the A+B resins they use in most of the experiments) and a slightly modified slicer software to turn your 3d models to G-Code.
    The gel seems pretty cheap to make as well and is re-usable, why hasn’t anyone turned this into a commercial product I wonder..

  3. I’ve seen the photo cured tanks of gel in use. Both laser and three projector type.
    I’m wondering of a fish tank of standard cooking gelatine could be used as a support structure and a long needle like extrusion head could be used

  4. Makes me think of oogoo, (silicone caulk curing with some water added). The water alone would be the support structure filling a tank as the printing proceeds upwards. The result would be ready for use just a short while after printing completes.

  5. Did anyone else notice in that second video that the printer seems to finish an inner-shell then go back down a few layers to continue an outer shell? Did it really do that? What slicer would one use to get that behavior?!?!

    I’m really hating the way these videos were embedded. Oversimplified UIs suck! The only controls seem to be pause/unpause and play again once the video is over. It would have been nice to be able to quote the point in seconds where I see this, likewise it would be nice to be able to rewind to that spot and play it multiple times to see if what I think I saw is really what happened.

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