Evanston, Illinois – Engineers at Northwestern University have developed a robotic leg powered by soft artificial muscles strong enough to kick a volleyball off a pedestal, showcasing remarkable lifelike strength and sensing ability.

The life-size leg features three artificial muscles—a quadricep, hamstring, and calf—connected by elastic tendons to rigid plastic bones. These parts work together to bend the knee and ankle joints while absorbing impacts and delivering powerful, controlled movement.

“This includes bringing together not only practical artificial muscles, but also bone- and tendon- or ligament-like components to robotics,” said Ryan Truby, senior author of the study. “If we can do that… robots will be able to harness the mechanics of softer materials to become more efficient.”

Each muscle is created from a 3D-printed cylindrical structure called a “handed shearing auxetic” encased in a rubber origami-like bellows. These actuators can extend up to 30% of their length, lift objects 17 times heavier than themselves, and dynamically stiffen like real muscles.

To mimic sensing in biological limbs, the team added flexible 3D-printed sensors that detect muscle stretch and contraction by measuring changes in electrical resistance.

The entire leg is compact and battery powered, capable of bending its knee thousands of times per hour without external equipment.

“By engineering new materials for robotics with the performance and properties of biological musculoskeletal systems, we can build robots to be more resilient and robust for real-world use,” Truby said.

The study was published on July 24 in Advanced Materials and supported by the Office of Naval Research and Northwestern’s Center for Engineering Sustainability and Resilience.

Podcast: Play in new window | Download