Robotic Hand with Plastic Bones, Ligaments, and Tendons Printed in One Run
In what they claim is a world first, researchers at Switzerland’s ETH Zürich university have 3D printed a robotic hand with plastic bones, ligaments, and tendons in a single process. Slow-curing thiolene polymers are the secret sauce in this application. 3D-printing technology that uses a laser to scan each polymer layer and compensate for surface imperfections in subsequent layers rather than scraping them away is also instrumental in achieving this milestone.
Advantages of slow-curing polymers
Slow-curing polymers have decisive advantages over fast-curing plastics — elastic properties are enhanced and they are more durable and robust, according to ETH Zürich researchers. A technology developed collaboratively by researchers at the Swiss school and Medford, MA–based Inkbit, an MIT spin off, enables the use of slow-curing thiolene polymers as well as combinations of soft, elastic, and rigid materials.
Thiolene polymers are ideal for printing the elastic ligaments of the robotic hand, according to Thomas Buchner, a doctoral student in the group of ETH Zürich robotics professor Robert Katzschmann and first author of the study. “They have very good elastic properties and return to their original state much faster after bending than polyacrylates,” which they had been using previously in 3D printing applications, said Buchner. In addition, the stiffness of thiolene can be fine-tuned to meet the requirements of soft robots, which are less likely to injure human co-workers than their rigid counterparts and are better suited for handling fragile goods, Katzschmann explains.
Modified 3D-printing technology
To accommodate processing of the slow-curing polymers, the researchers had to modify the 3D-printing process. Typically, nozzles deposit the material in layers, and each layer is cured immediately with a UV lamp. Surface irregularities are then scraped away by a device after each curing step. This only works with fast-curing polyacrylates, according to the researchers, because slow-curing polymers would simply gum up the scraper. Instead, they use a 3D laser scanner that immediately checks each layer for surface defects. “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,” explains Wojciech Matusik, a professor at MIT and co-author of the study.
Inkbit developed the new printing technology while ETH Zürich researchers developed robotic applications and helped optimize the technology for use with slow-curing polymers. The US and Switzerland-based researchers jointly detail the technology and sample applications in a paper published in the journal Nature.
Using biomimetics to print a fluidic pump
In addition to the 3D-printed robotic hand, the paper published in Nature describes a robotic heart with a fluidic pump and integrated valves inspired by a mammalian heart. Actuation membranes, one-way valves, and internal sensor cavities are embedded in the heart’s chamber. “The integrated valves and pumping membranes were inspired by the geometries and mechanisms in mammalian hearts, which have already been optimized by nature. Our easy-to-remove support material . . . allowed us to print several small and large cavities with thin, soft membranes and rigid walls in one process. Similar pump designs were previously only possible through the casting or injection molding of individual components, both of which were followed by time-consuming and labor-intensive assembly,” the researchers write.
At ETH Zürich, Katzschmann’s group will use this technology to explore additional applications. In the United States, Inkbit plans to offer a 3D-printing service that applies this technology for its customers and to commercialize the printers.