Soft Robots: 3D Printing Artificial Muscles




About: I believe that the purpose of life is to learn how to do our best and not give in to the weaker way.

Using a standard filament 3D printer, artificial robot muscles can be directly printed. These air powered muscles can be used in all kinds of robots or powered prostheses.

Intro pic shows a six muscle flower robot activated. Such a simple robot could be used to indicate air pressure, temperature or as a protective enclosure that opens up. Pic 2 shows it closed.

This instructable shows how to make the flower muscles and a pull muscle which is detailed in step 7.


Step 1: How It Works

Previously I have made artificial muscles using a 3D printer by printing molds and casting silicone in them. See here:
That is a fairly involved method and does not produce the same precision as directly 3d printing.

This is a more direct method where the muscles themselves are directly 3D printed using a flexible filament called Ninjaflex. The printing pattern of a 3D filament printer leaves many microscopic holes that will not hold air pressure. So, after printing, the muscles are dip-coated in an flexible elastomeric glue to seal the holes. This allows them to hold air pressure of 22 PSI or higher.

I used a Makerbot Replicator 2 to make these muscles, but other filament printers that can print Ninjaflex can be used.

This is still at the early stage of experimentation, but it shows great promise for producing muscles that can replace servos and gear-motors in robots. This will make them considerably less expensive and when used in soft robots, make them more human friendly to touch and be around.

A Stereo-lithography printer using flexible resins, would make it possible to produce smaller and more precise types of muscles and robot skin that a filament printer cannot. More intricate air channels and unusual shapes that do not need supports could also be printed. A flower robot like this could be printed assembled in one piece.

Step 1 pic shows the flower opening when all six muscles are pressurized at 22 PSI.

Step 2: Designing 3D Printable Artificial Muscles

All of these muscles were designed using a free program: 123D Design.

To begin the design, the basic shape is drawn and then extruded as a solid.

It is then hollowed out to create walls that are .026" thick. Size the solid to produce an internal air channel around .002" thick. This wall thickness produces 2 shell walls that will fuse together solidly. This minimal thickness works well for a Makerbot Replicator 2 printer. For larger and more robust muscles a wall thickness of .053" will produce 4 shell walls. For a different printer, you will have to experiment with different wall thicknesses that work with your particular settings.

a square nozzle with a square hole for tubing is attached and the muscle is done.

Step 3: Supplies

Makerbot Replicator 2 or other filament 3D printer

Ninjaflex filament.
Available from:

MEK solvent available from most hardware stores.

Loctite fabric glue available from Walmart or Amazon. I tried a few dozen glues, paints and sealers, and the Loctite glue was the only one that would fuse well to the Ninjaflex and remain flexible. It also glues well to vinyl tubing and acrylic materials.

Mason Jar. Mason jars work well for holding solvents and solvent glues and paints. If you reverse the lid then the metal will be against glass and the rubber seal won't dissolve.

1/8"vinyl tubing and fittings-available from:

.25" clear acrylic tubing available from:
This is for the flower stem, but it could be printed in PLA instead.

Step 4: 3D Printing the Robot Flower Muscles

Flower muscles are the smallest volume of muscle that can produce a large amount of movement. They could be used as indicators of pressure, temperature or other parameters. They can also be used to latch moving pieces or to open and close protective enclosures. Controlled as separate petals they could be used to indicate numbers. They could also be used to create facial expressions on a robot head.

The muscles and muscle hub and petals were printed in Ninjaflex with a Makerbot Replicator 2 using the following settings:

No supports
Infill: 100 per cent
Shells: 2
Layer Height: .2mm
Temp: 225 C
Speed Extruding: 30 mm/s
Speed Traveling: 150 mm/s

Step 4 pic shows a single printed and sealed muscle relaxed.

Pic two shows the muscle pressurized.

Step 5: Sealing the Flower Muscles

After printing a short piece of vinyl tubing is inserted into the nozzle. Then, the artificial muscle is dipped in a sealant and allowed to dry for 2 hours. After drying, it is dipped again and then allowed to dry overnight. This will usually create a permanent seal. Occasionally, after pressure testing the muscle underwater, leak points will be revealed which can be sealed with a dab of glue.

This should be done under a vent hood or outside with a fan to blow the solvent fumes away.

The sealant is composed of Loctite Fabric Glue that is thinned with 10 to 20 per cent MEK solvent by volume. The MEK slightly dissolves the Ninjaflex resulting in an extremely good fusion of glue and Ninjaflex. Adding more MEK will tend to swell the Ninjaflex and make some muscle types hard to seal.

Step 6: Assemble the Robot Flower

After six muscles have been sealed with a vinyl tube in the nozzle, they should be tested under pressure. Once they are leak free they are glued to the petals as in the step 6 pic.

The hub should be dipped twice in sealant and left to dry overnight before gluing the muscles to the holes in the hub.

Finally a .25 clear acrylic or PLA printed tube (sealed) should be glued to the hub and once dry the whole flower tested under pressure in water.

Step 7: 3D Printing Pull Muscles

Artificial muscles that push are in many ways more efficient than muscles that pull as they do not require a shell around them or tendons to work. There are however, many places where a pull muscle with tendons is required.

ZIG-Zag Muscles
The zig zag muscles are the best design I have found so far for getting maximum expansion from a minimal resting volume of muscle.

The step 7 pic shows the muscle lifting a one pound weight. This muscle has an expanded volume of 2.5 cu. in. and can lift more than 4 pounds.

Pic 2 shows the muscle relaxed.
Pic 3 shows the components of the pull muscle

These muscles could be scaled up considerably for more power.

Step 8: Other Possibilities

Experimental Muscle Types
Step 8 pic shows just a few of the muscle types I have experimented with. I have barely scratched the suface of what is possible in the 3D printing of artificial muscles. Pic 2 shows the muscles pressurized. The largest blue elbow muscle is 1" x 1" x 3" long.

The Future Of Robotics
I believe that the future of robotics, if it is to become more affordable and useful, will involve the 3d printing of soft robot muscles and skin teamed up with 3d printed stiff bones and shells. This will minimize the number of expensive servos and gear-motors that will necessary. It should eventually be possible to print the muscles, bones, and skin of a robot in one print.

3D Printing Forms For Casting Muscles
If you want to cast muscles in 3D printed forms using silicone or other flexible materials see here:

3D Printing Servo Controlled Valves
You can 3D print your own valves that are easy to control with a microcontroller:



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    18 Discussions


    26 days ago

    Does this discuss how to make the muscle itself contract?


    Question 4 months ago

    I would like to ask the author how to maintain air pressure, I follow the above process to do, to increase the air pressure to the muscle pipeline when the muscle will not deform, I do not know why.


    3 years ago

    You mentioned that the zig-zag muscles are the best design you have found for maximum expansion. Have you as yet tried a spiral muscle design?


    3 years ago on Introduction

    Fascinating work. I'm not sure if I missed it, but do you have a video of the flower opening and closing?

    2 replies

    Reply 3 years ago

    Sorry, I am too busy working on new 3d printed muscles to waste time on videos that do not show more than still pictures. If you bother to try it, you will see that it works exactly as described.


    Reply 3 years ago

    I ask because I am interested in your work despite not having a 3D printer myself, not because I am too lazy to try.

    I look forward to the new stuff you are working on then.


    3 years ago on Introduction

    Hi! Could you please open source some of your other muscle designs? Also, I was wondering how I could go about building a tendon system to mimic the musculoskeletal systems of the body. Thanks!


    4 years ago on Introduction

    What happens when you do not glue-seal the ninjaflex? Is it a slow loss of pressure?, or just much less pressure capacity, and rapid leak with inflation?

    I thought TPEs were supposed to have good air retention. (favorite materials for air beds and inflatable boats now)

    have you tried water as the actuating fluid?

    3 replies

    Reply 4 years ago on Introduction

    It is a fast loss of air pressure due to the many holes that are left in the 3D printing process. Sealing is necessary to create usable muscles.

    TPEs do have good air retention if they are extruded or cast in solid forms.

    Water can be used but it is messy and harder to test for leaks and make repairs.


    Reply 4 years ago on Introduction

    > fast loss of air pressure due to the many holes that are left in the 3D printing process

    I was also wondering if relatively flexible nylon (or taulman TPE) would make a good air vessel. To stay flexible, thinner wall thickness seems obviously needed. Do you think that thicker models would still need coating? Lower layer heights with more layers? Higher printing temp?

    Ninjaflex is "highly affected by solvents/acids" (though I'm unsure which ones). Would something like an acetone (smoothing) bath serve to seal up those pores/holes?

    Thank you for amazing project, and reply.


    Reply 4 years ago on Introduction

    Flexible nylon could work. Sadly, there are almost no easily available flexible glues that will fuse to nylon. I tried dozens of combination's of Ninjaflex and glues before I found one that would work.

    If you look at a filament printed object under a microscope, you will see that no matter the slicing settings, there will be gaps left that will leak under pressure.

    To create air tight filament printed muscles that do not require a coating will require new technology that does not exist except in unaffordable industrial printers.


    The fact is your project inspires for several more robotic gadgets. Great project, I raise my hat.

    Wow very cool. Once when I am done building my 3d printer I think you will hear from me again.


    4 years ago on Introduction

    What an inspiring instructable! I've had some ninjaflex for a month or two but had not figured out what to do with it. Now I will have to try this. Awesome!

    1 reply

    Reply 4 years ago on Introduction

    Hey Rachel! If you're struggling to get started with printing NinjaFlex, we've just started a new forum that puts you in direct contact with NinjaFlex engineers -- check it out at

    Or, follow us on Twitter to see what others are printing with NinjaFlex!


    4 years ago on Introduction

    How inventive! We love seeing all of the creations that 3D printers are making with NinjaFlex and this one is amazing - great job Mikey!


    4 years ago on Introduction

    Wonderful! Please continue your good work and postings. Thank you.