The team 3D printed a robotic hand in one go via the slow-curing plastics method. (Image Credit: ETH Zurich/Thomas Buchner)
For the first time, ETH Zurich and US startup Inkbit researchers created a new laser scanning technique to 3D print a robotic hand, achieved via slow curing, with ligaments, tendons, and bones made of various polymers. According to the team’s paper, they printed different parts of the hand simultaneously instead of assembling them after printing. Researchers can use this technology to combine rigid, soft, and elastic materials and print complex, durable robots.
The team used openly available MRI data to model all the bone structures found in a person’s hand. Their finished hand has sections with soft tendons and capsules surrounding the joint areas and tendons that are internally reinforced with a rigid material for a load-bearing structure. It even comes with fishing line tendons interfacing with the printed tendons. All of these connect with motors.
“We wouldn’t have been able to make this hand with the fast-curing polyacrylates we’ve been using in 3D printing so far,” says 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 that case, thiolene polymers are perfect for the robotic hand’s elastic ligaments.
Also, the thiolenes’ stiffness can be sufficiently adjusted so that it meets soft robotics requirements. “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,” Katzschmann says.
3D printers use a nozzle to eject material in viscous form at every point, printing objects layer-by-layer. Then, a UV lamp quickly cures all the layers. Surface irregularities were usually removed by a scraper device after a curing step was finished. However, the method is only applicable for fast-curing polyacrylates and not slow-curing polymers like epoxies and thiolenes because the leftover material would clog the scraper.
The team used polymers with different elasticity to print the hand layer-by-layer. (Image Credit: Buchner TJK et al., Nature 2023)
So, the researchers equipped the 3D printer with a 3D laser scanner to detect surface irregularities on each layer before the systems proceeded with the next material type. “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,” says Wojciech Matusik, a professor at MIT and co-author of the study.
The slow-curing plastics are capable of bending and returning to their original shape. That can pave the way toward more realistic functioning prosthetics. Their new printing technique is more advantageous compared to fast-curing projects since it improves durability and elasticity. Additionally, it can help researchers replicate nature more precisely, as shown with the robotic hand.
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