Prototype 3D-printed soft hand grips eggs and a 1 kg bottle

An egg sits in the grip of a robotic hand, its fingers bending around the fragile shell instead of crushing it. The same 3D-printed soft hand also lifted a 1 kg water bottle and held glass bottles, an egg carton and a computer mouse, in tests by researchers in South Korea.

The hand’s material was the difficult part. Digital Light Processing, or DLP — a 3D-printing method that cures liquid resin with light — can produce complex shapes quickly. But making a resin more elastic and durable usually makes it too viscous to flow properly through the printing process. Thinning it improves flow while weakening its stretch and strength.

Professor Seungchul Lee’s team at the Korea Advanced Institute of Science and Technology worked with Dr. Jongbeom Na’s group at the Korea Institute of Science and Technology and Professor Bumsoo Park of Seoul National University of Science and Technology. They measured how different formulations stretched, hardened, flowed and responded to light, then used machine learning to identify a combination that balanced those properties.

The resulting elastomer printed reliably on a DLP printer and stretched to more than six times its original length when pulled. The researchers used it to make soft actuators — devices that use air pressure to create muscle-like movement. Inflated actuators expanded like balloons and bent in a motion resembling a human finger. The study appeared in Nature Communications.

So what changes in practice? The study reports a demonstration with a soft robotic hand. But the approach could shorten the search for materials used in soft robots that touch people, wearable devices and medical devices fitted to individual patients: instead of testing every possible formulation directly, researchers can use experimental data to guide the next candidates.