Elastomer inks for 3D printed objects

For engineers working on wearable technology and soft robotics, an important issue is keeping it lightweight. Wearing heavier materials can be uncomfortable because they require more energy to move.

Elastomers (synthetic polymers with a variety of mechanical properties) are often used in such applications because they can be stretchable or rigid. However, producing elastomers that can be molded into complex three-dimensional structures with varying stiffness levels has been challenging.

To overcome this difficulty, scientists created DNGE (Double Network Granular Elastomer), which can be three-dimensionally printed and change its mechanical properties over short distances.

Example of DNGE (3D printable dual mesh granular elastomer) © Titouan Veuillet
Example of DNGE (3D printable dual mesh granular elastomer) © Titouan Veuillet

Eva Baur, a doctoral student in the Soft Materials Laboratory, used DNGE to print a finger prototype with hard “bone” surrounded by flexible “meat.” The finger serves as an example of how technology can be used to create flexible and comfortable devices that can bend and extend while remaining stiff enough to manipulate objects.

Because of these advantages, the researchers believe DNGE could make it easier to build wearable devices, sensors, and soft actuators without the need for large, bulky mechanical joints.

The design of two elastomeric networks is the secret to DNGE’s adaptability. First, elastomer particles are created using oil-in-water emulsion droplets. After dissolving in the precursor solution, the particles absorb the elastomer components and swell.

The 3D printing ink is then loaded into the bioprinter using expanded particles to create the appropriate structures. The precursors of the 3D printed structure are polymerized to form a second elastomer network that makes the entire structure stiff.

The composition of the first network defines the stiffness of the structure, while the composition of the second network determines its fracture toughness. Therefore, both networks can be tuned independently to obtain a combination of fatigue resistance, toughness, and stiffness.

Using elastomers instead of hydrogels used in tip methods provides the added benefit of producing water-free structures, thereby improving their stability over time. In addition, DNGE can be produced using commercially available 3D printers.

Esther Amstad, head of the Soft Materials Laboratory at EPFL’s School of Engineering, said: “The beauty of our approach is that anyone with a standard bioprinter can use it.”

The ability of DNGE to support movement in one direction while limiting movement in another presents a fascinating potential application in movement-guided rehabilitation systems. Further developments in DNGE technology could produce prosthetics or even movement guides to assist surgeons. Another application area is sensing remote motion, such as seafloor exploration or robot-assisted agricultural harvesting.

Journal reference:

  1. E. Baur, B. Tiberghien, E. Amstad, 3D printing of dual-network particle elastomers with locally varying mechanical properties. adverb. Matt. 2024, 2313189.DOI: 10.1002/adma.202313189

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