Design and Fabrication of an Elastomeric Unit for Soft Modular Robots in Minimally Invasive Surgery

The overall goal of this protocol is to fabricate a soft unit to be integrated into a multimodal manipulator for use in minimally invasive surgery. This method can help answer key questions in the field of soft robotics by showing how to optimize the fabrication procedure of a soft manipulator with high dexterity and stiffening capabilities. The main advantage of this technique is that it is very fast and low cost.

In addition, the final product can be replicated to produce a multimodal architecture improving the performance of the manipulator. Generally, individuals new to this method will struggle because silicone modules with complex shapes usually require a multi-phase publication procedure was optimization is often time consuming. Visual demonstration of this method is critical as the external shift fabrication steps are difficult to learn because they are based on a commercial bright shift that is completely modified for the final purpose.

Demonstrating the procedure will be Jada Bon PhD student and Margarita Blanco, research assistant from my laboratory. Add 12 grams of part A and 12 grams of part B in the same Petri dish and mix them together to prepare the silicone. Then place the mixed silicone in a DGAs under one bar of vacuum pressure.

Keep the material under vacuum until all of the bubbles have been removed from the silicone material. This typically takes about 10 minutes once the materials are completely free from the presence of bubbles, release the vacuum and remove the silicone, which is now ready to use. Assemble the mold by first inserting the stiffening cylinder and the top of the chambers into cap A, and then closing the shells around it.

Pour the silicone inside the assembled mold up to the edge of the shells. Set the oven to a temperature of 60 degrees Celsius and place the filled up mold into the oven. Leave the silicone curing for about 30 minutes.

Remove the external shells and cap A from the cured silicone. Next, insert the silicone modules from the basis of the chambers and the stiffening cylinder inside cap B.Close the shells again around the module, sliding them 10 millimeters upward in order to have a gap of 10 millimeters between the top surface of the module and the edges of the shells. Pour additional silicone inside the rearranged mold up to the edge of the shells on the top side.

Cure the freshly poured silicone in an oven at 60 degrees Celsius for about 30 minutes. Remove the external shells cap B and all of the chambers except the stiffening cylinder. Cut three millimeter diameter silicon tubes to a length of about 30 centimeters.

Put silicon glue around the outside of one end of each tube for the first 10 millimeters. Then insert the tubes inside the two millimeter dedicated channels. In the silicon unit.

Allow the glue to cure for 12 minutes. At room temperature, cut 70 centimeters of an expandable braided sheath and then insert a three centimeter diameter 25 centimeter long metallic cylinder inside the sheath. Next, push down and force the sheath onto the cylinder in order to create crimps.

Mechanically, fix the sheath in place with a clamp and heat it with a heating gun at 350 degrees Celsius for two to three minutes. In order to obtain a permanent deformation, let the sheath cool down to room temperature and then remove the internal cylinder. Pass the tubes from the silicon unit through the holes of cap C.Then pour three grams of the DGAs silicone into cap C and slide the bottom side of the module previously fabricated into cap C.Slide the crimped sheath around the module and push the first crimps inside cap C and dip them into the freshly poured silicone.

Set the oven to a temperature of 60 degrees Celsius and place the sample in for about 20 minutes. Once the silicone is cured, repeat the same process on the other side using cap D to fix the sheath at the top side. Once the silicone is also cured at the top side, remove both cap C and cap D from the bottom and the top of the module respectively.

Finally, remove the stiffening cylinder from the entire silicon unit. Pour some grams of liquid latex into a plastic glass and immerse the cylinder for the membrane inside the liquid latex until the surface is completely covered. Then remove it from the latex and let the membrane dry under the hood for 20 minutes.

Then form a second layer by again immersing it in the latex and letting it dry for an additional 20 minutes. Once dry, remove the membrane from the mold. Cut a two millimeter diameter tube to a length of 30 centimeters.

Then take a 10 millimeter by 10 millimeter piece of nylon tissue and close one end of the tube with this tissue using superglue. Next, weigh around four grams of granulated coffee and fill the membrane as much as possible with the powder. Insert the filtered end of the tube inside the filled membrane and fix it around the tube.

Using a plastic film, apply a vacuum on the other side of the tube to stiffen the membrane and then insert the membrane inside the empty central channel of the silicon module. Next, glue the ends of the stiffening membrane to the silicone module. Close the ring around the bottom side of the module.

Pour some fresh silicone into the ring in order to level the surface and let the silicone dry under a hood. Finally, remove the rings and repeat the procedure for the top side of the module. When all three chambers are simultaneously actuated with the same pressure, the module elongates starting from the length of 50 millimeters at zero bar, the module reaches 83.3 millimeters with 0.65 bar of pressure, which corresponds to an elongation of 33.3 millimeters, which is about 66%Using only one or two of the chambers will cause the setup to bend.

The module is able to bend up to 120 degrees in the case of one chamber bending and up to 80 degrees for two chamber bending. In both cases, a significant bending starts when the chambers are inflated by about 0.3 bar. The module is able to generate forces from 24.1 Newtons when one chamber is actuated up to 47.1 newtons When three chambers are inflated.

Once master, this technique can be done in four hours if it is performed properly. This technique paves the way for researchers in the soft robotics field to explore the combination between fluidic, actation and variable stiffness technologies for soft structures. After watching this video, you should have a good understanding of how to manage the molding of soft materials and how to integrate flexible 3D calculators with a variable stiffness mechanism.

Don't forget that working with silicone, a latex can be really dangerous and pre precautions, such as working under fume hood and wearing gloves should always be taken while performing this procedure.