Real-muscle robots gain threefold speed and 30× force with new tendon system

MIT engineers have pushed biohybrid robotics into a new era with lab-grown muscles that don’t just twitch robotic parts but amplify them with serious power. In a breakthrough that reimagines how living tissue can drive machines, researchers at MIT have developed artificial tendons made from tough, flexible hydrogel.

These rubber band–like connectors dramatically boost the speed, strength, and durability of muscle-powered robots. Biohybrid robots, the machines built from both living muscle tissue and synthetic parts, have long been limited by how much force their biological components can deliver.

But MIT’s new muscle-tendon system changes that equation by bridging muscle to skeleton more efficiently. And the numbers tell the story: the tendon-enhanced gripper moved three times faster and with 30 times more force than one powered by muscle alone. Tendon tech transforms The research team, led by Ritu Raman, assistant professor of mechanical engineering at MIT, developed a modular design that links lab-grown muscle to robotic skeletons using hydrogel tendons.

We are introducing artificial tendons as interchangeable connectors between muscle actuators and robotic skeletons, Raman says. Such modularity could make it easier to design a wide range of robotic applications. The tendons are engineered from hydrogels developed in the lab of co-author Xuanhe Zhao, known for creating gels that are tough, stretchy, and capable of sticking to biological tissues and synthetic materials.

The team modeled the ideal stiffness of each tendon by simulating the system as three springs: the muscle, the tendon, and the gripper skeleton. This allowed them to calculate exactly how strong and flexible the hydrogel cables needed to be. Once fabricated, the tendons were attached to either side of a small strip of lab-grown muscle. Each tendon was then wrapped around posts on the robotic gripper’s fingers, a design created by MIT professor Martin Culpepper.

Small muscle, big force When the muscle contracted under stimulation, the hydrogel tendons transmitted force far more effectively than muscle tissue alone. This allowed the robotic gripper to “pinch” with unprecedented efficiency, repeating the action more than 7,000 times without degrading. Overall, the addition of artificial tendons boosted the system’s power-to-weight ratio by 11x, meaning far less muscle was needed to achieve far greater output.

You just need a small piece of actuator that’s smartly connected to the skeleton, Raman says. By acting as a biomechanical bridge, soft enough for muscle, strong enough for rigid parts, the tendons eliminate the tearing and detachment problems that have plagued previous designs.

Biomedical engineer Simone Schürle-Finke of ETH Zürich, who was not involved in the work, says the approach greatly improves force transmission, durability, and modularity. Raman’s group is now developing additional elements, including skin-like protective casings, to move biohybrid robots closer to real-world use. The study appears in Advanced Science.