Slow-curing polymers 3D printed into robotic replica of human hand

The development from ETH Zurich and MIT spin-off Inkbit makes 3D printing suitable for slow-​curing polymers whose properties include elasticity, durability and robustness.

Consequently, researchers can now 3D print complex, more durable robots from a variety of high-​quality materials. According to ETH, the new technology also makes it possible to combine soft, elastic, and rigid materials. The researchers can also use it to create delicate structures and parts with cavities.

“We wouldn’t have been able to make this hand with the fast-​curing polyacrylates we’ve been using in 3D printing so far,” said Thomas Buchner, a doctoral student in the group of ETH Zurich robotics professor Robert Katzschmann and first author of the study. “We’re now using slow-​curing thiolene polymers. These have very good elastic properties and return to their original state much faster after bending than polyacrylates.”

In addition to being suitable for the elastic ligaments of the robotic hand, the stiffness of thiolenes can be fine-​tuned to meet the requirements of soft robots.

“Robots made of soft materials, such as the hand we developed, have advantages over conventional robots made of metal. Because they’re soft, there is less risk of injury when they work with humans, and they are better suited to handling fragile goods,” said Katzschmann.

3D printers typically produce objects layer by layer, with nozzles depositing a material in viscous form that are then cured with a UV lamp. Previous methods involved a device that scraped off surface irregularities after each curing step, which works for fast-​curing polyacrylates but is unsuitable for thiolenes and epoxies that would gum up the scraper.

To accommodate the use of slow-​curing polymers, the researchers added a 3D laser scanner that immediately checks each printed layer for any surface irregularities.

“A feedback mechanism compensates for these irregularities when printing the next layer by calculating any necessary adjustments to the amount of material to be printed in real time and with pinpoint accuracy,” said Wojciech Matusik, a professor at the MIT and co-​author of the study, which is published in Nature.

Inkbit was responsible for developing the new printing technology whilst ETH Zurich researchers developed robotic applications and optimised the technology for use with slow-​curing polymers.

Katzschmann’s group will now use the vision-controlled jetting technology to design more sophisticated structures and develop additional applications.