8. SOFT ROBOTICS¶

INSPRIATION¶

Visoule Projects by Julie Taris - Fabricademy Student making an inflatables hoodie
Matthew Szosz - shapes glowing sheets of glass by pulling them from the oven and inflating them with compressed air, causing their flowing forms to solidify into glass within seconds
3D Printed Blooming Flowers by Mikaela Holme - inflatable head piece with 3D printed flowers
Harri Store - a shop that is selling inflatable fashion pieces with inspiring shapes.
Unflatables by Saskia Helinska - final fabricademy project which is exploring the potential uses of soft robotics, especially inflatables
Soft Robotic Mask by ]AdiM33](https://www.instructables.com/member/AdiM33/) - a silicon face mask that responds to facial expression

INFLATABLES¶

Heat Press Inflatables¶

One simple method for making inflatables is to use a heat press along with vinyl or TPU and baking paper. Start by cutting your desired shapes out of the baking paper with scissors. Place the cut-out form between two sheets of TPU and then press them together using the heat press. Before putting the vinly under the heat press the surface has to be cleaned with ethanol.

I like this grafik made by Adriana Cabrera which visualizes the process very well. Here the process is shown with vinly but with TPU is also works

Be sure to consider how the air will flow inside your inflatable. The longer the distance from the pump, the less airflow you’ll get, so plan your air channels carefully. Remember to leave an opening for the air pump.

I chose to work with TPU instead of vinyl, though waterproof polyester fabrics can also be heat pressed effectively. Using a dense fabric, such as tightly woven silk, can even replace baking paper for certain applications. For greater precision, you can also cut the baking paper or TPU using a laser cutter.

Test 1

Test 2

Silicon Inflatables¶

For the silicon inflatables, we used 3D-printed molds from the lab. The molds consist of two parts: one has a patterned surface with grooves for the airflow, while the other is flat and serves as the cover.

Step by Step:

Mix the EcoFlex silicone in a 1:1 ratio and stir thoroughly. During mixing, a chemical reaction starts that cures the silicone, so you need to cast it quickly.

Place the mold on a vibrating surface to remove any air bubbles.
Pour the liquid silicone into both mold parts and let it cure for about 4 hours.
Once cured, carefully remove the pieces from the molds.
To connect the two silicone parts, mix a small batch of silicone again to use as glue.
Apply the silicone mixture to the flat surface of one piece.
Press the two parts together gently and let them cure for another 4 hours.
After curing, test the inflatable with an air pump to ensure proper sealing and airflow.

Biofabricated Inflatables¶

Alginate Inflatable

Since I was sick this week, I wasn't able to follow every step of the process, so I followed the description of Isabel Leonard from last year’s documentation to see how the alginate inflatable was made:

Although I missed most of the main fabrication, I did test the casting of some alginate the group had prepared. First, I wrapped a loop of denim and sprayed it with alginate. I then cast a layer of alginate onto it. Afterward, I sprayed the surface with calcium chloride to begin the gelling process and wiped off any excess solution. I poured another layer of alginate on top and again sprayed it with calcium chloride.

Next, I made a small hole in the material and inserted an air pump to inflate it. This step worked to some extent. After inflating, I quickly removed the pump and poured calcium chloride inside to ensure the alginate would cure from the inside as well. I then added the pump again so that the calcium chloride could distribute throughout the inflatable, helping to cure the structure everywhere.

The process worked, but unfortunately, the recipe did not contain enough alginate, causing the inflatable to tear rather quickly. I tried several times before realizing this was the problem. Despite the setbacks, I managed to record a video of the attempt that worked best.

The group did also some experiemtns with gelatine which you can find at Maddies documentation.

Fish Skin Inflatable¶

Flora and I experimented with making an inflatable object from the fish-skin leather we produced last week. We sewed a small rectangular shape, leaving a small opening to turn it inside out. After turning the piece, we closed the opening with stitches, leaving just a small hole for inserting the air pump.

It worked surprisingly well. We initially thought we might need to seal the seams because of the tiny holes made by the sewing needle, but that turned out not to be necessary.

To explore another variation, we sewed two round shapes connected by a line in the middle so that it would only inflate around the outer areas. Unfortunately, the sewing machine’s stitches allowed some air to escape, which prevented the shape from fully inflating. Flora tried sealing the seam with wax, but this did not make much difference.

In the end, we concluded that because of the two stitched lines, there was not enough surface area left for proper inflation. Next time, it would be better to sew only one line or increase the overall size of the shape to allow more space for inflation.

3D Printed Shape with Hydrogels¶

This technique was completely new to me. The main idea is to create a shape made of TPU consisting of several small, interconnected chambers. Each chamber is filled with hydrogels—the same type commonly used for watering plants—which are enclosed within the structure.

When placed in water, the hydrogels absorb the liquid, expand, and push against the chamber walls. This causes the entire shape to bend and transform, resulting in a soft robotic movement that is manually activated through water.

We 3D printed the shapes using heat-reactive TPU filament and filled them with hydrogel balls. Asli prepared the file in Rhino and managed the printing process. The shape was designed with a hollow interior, allowing it to be partially filled with hydrogels during the printing phase.

The print was paused once it reached a suitable height for filling. Using heat-reactive material proved especially practical, as it changed color based on temperature, letting us easily see whether the shape was warm or cold.

After the print was paused, we carefully removed the small filament threads that had formed inside each chamber. Once cleaned, the shapes were filled halfway with hydrogels. Because the material had cooled by then, we used a heat gun to warm it slightly before resuming the print. This ensured that the new layers adhered properly to the previously printed sections.

The top layer of the shape has a slightly permeable structure, allowing water to pass through. When placed in water later, this permeability enabled the hydrogels to absorb the liquid and expand. After soaking the shape in cold water, it turned red due to the temperature but maintained its structure. After about 30 minutes, the shapes contracted, as visible in the images.

Test 1

In the first test, the chambers were filled about three-quarters full with hydrogels. As the hydrogels expanded significantly in water, they broke the chamber walls. Additionally, the top layer did not bond well with the lower part of the print.

*3D printed shapes filled with Hydrogels - dry and after soaking in water*

Test 2

In the second test, we filled the chambers only halfway with hydrogels to prevent damage to the walls. We also used a heat gun to warm the surface before resuming the print, improving adhesion and structural stability.