Soft, pliable robots are charting new terrain in engineering, allowing machines to replicate the flexibility of biological appendages like octopus limbs and human hands. Now, a new robot design created at Harvard is even more dexterous than previous technologies. It can replicate the uber-complex movements of human joints, bending and twisting like a finger, wrist, or knee.

When you bend your thumb in toward your wrist, it’s not just a single movement; that makes it difficult for a machine to mimic. Recreating organic movement in an artificial body requires multiple actuators, the part of a machine that controls a movement. “The design is so complicated because one actuator type is not enough to produce complex motions,” Fionnuala Connolly, one of the paper’s authors and a graduate student in Harvard’s engineering program, said in a press statement. “You need a sequence of actuator segments, each performing a different motion."

The Harvard engineers tackled this problem by created a mathematical model of a fluid-powered movement. They used this model to design a finger-like soft robot that can bend and twist at the same time in response to only one pressure source.

This type of robotic design could be used in the future to create robotic arms or wearables that assist with human movement. The research paper is available in PNAS.