Inks for 3D printing flexible devices without mechanical joints

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The lab’s DNGE prototype “finger” has a rigid “skeleton” surrounded by flexible “flesh.”Photo credit: Adrian Alberola

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The lab’s DNGE prototype “finger” has a rigid “skeleton” surrounded by flexible “flesh.”Photo credit: Adrian Alberola

EPFL researchers aim to use elastomer-based inks to 3D print next-generation soft actuators and robots with objects that locally change their mechanical properties, eliminating the need for cumbersome mechanical joints.

For engineers working on soft robots or wearable devices, keeping things light is an ongoing challenge: Heavier materials require more energy to move and can cause discomfort in the case of wearable devices or prosthetics.

Elastomers are synthetic polymers that can be manufactured with a range of mechanical properties from rigid to elastic, making them popular materials for such applications. But until now, it has not been feasible to create elastomers that can be shaped into complex 3D structures ranging from rigid to rubbery.

“Elastomers are typically cast so that their composition does not change in all three dimensions over short length ranges. To overcome this problem, we developed DNGE: a 3D printable dual network granular elastomer that can changing their mechanical properties to an unprecedented degree,” Esther Amstad, director of the Soft Materials Laboratory at EPFL’s School of Engineering.

Eva Bauer, Ph.D., a student in the Amstad lab used DNGE to print a prototype “finger” that consists of rigid “skeleton” surrounded by flexible “flesh.” The fingers were printed to deform in predefined ways, demonstrating the technology’s potential to create devices that are soft enough to bend and stretch while remaining strong enough to manipulate objects.

With these advantages, the researchers believe DNGE could facilitate the design of soft actuators, sensors, and wearable devices without the need for bulky mechanical joints.The research has been published in the journal advanced materials.

Two elastomeric networks, twice the versatility

The key to DNGE’s versatility lies in the design of two elastomer networks. First, elastomer particles are produced from oil-in-water emulsion droplets. These particles are placed in a precursor solution, where they absorb the elastomeric compound and swell.

The swollen particles are then used to create 3D printing ink, which is loaded into a bioprinter to create the desired structure. The precursors polymerize within the 3D printed structure, forming a second elastomer network that stiffens the entire object.

The composition of the first network determines the structure’s stiffness, while the second determines its fracture toughness, meaning both networks can be fine-tuned independently to achieve a combination of stiffness, toughness and fatigue resistance.

Compared to hydrogels (the material used in state-of-the-art methods), using elastomers has the added advantage of creating a water-free structure, making it more stable over time. Most importantly, DNGE can be printed using commercially available 3D printers.

“The beauty of our approach is that anyone with a standard bioprinter can use it,” Amstad emphasized.

One exciting potential application for DNGE is in motion-guided rehabilitation devices, where the ability to support movement in one direction while limiting movement in another could be very useful.

Further developments in DNGE technology may lead to prosthetics or even movement guides to assist surgeons. Sensing motion over long distances, such as robot-assisted crop harvesting or underwater exploration, is another area of ​​application.

Amstad said the Soft Materials Laboratory is already working on developing such applications by integrating active elements such as responsive materials and electrical connections into DNGE structures.

More information:
Eva Baur et al., 3D printing of dual-network particle elastomers with locally varying mechanical properties, advanced materials (2024). DOI: 10.1002/adma.202313189

Journal information:
advanced materials

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