Scientists create artificial muscle for ‘wiggly’ robots

This development offered a potential leap forward for biohybrid robots—machines powered by lab-grown muscle fibres—making them more adaptable and flexible than those using traditional actuators or previous muscle constructs limited to single-directional movement.

Natural muscle tissue moves the body through the synchronised twitching of many aligned fibres. While some muscle groups run parallel, others form more complex structures, giving the body a wider range of motion. Inspired by this, researchers sought to engineer muscle tissue that mirrors the same level of sophistication.

The team’s approach centred on a stamping technique. They 3D-printed a handheld stamp with microscopic grooves—each approximately the size of a single cell. These grooves were then pressed into a hydrogel and seeded with muscle cells. As the cells grew, they aligned with the stamped patterns and formed functional muscle fibres. When activated, the fibres contracted in multiple directions, responding according to their alignment.

To demonstrate the technique’s capabilities, the team produced a structure modelled after the human iris, which naturally dilates and contracts via concentric and radial muscle fibres. Using skeletal muscle cells genetically engineered to respond to light, the researchers grew an artificial iris that replicated this multidirectional motion.

According to Ritu Raman, the Eugene Bell Career Development Professor of Tissue Engineering at MIT, this marked the first example of a skeletal muscle-powered construct that could generate force in more than one direction—something made possible through the precision of the stamping technique. The flexibility of this approach meant it could be adapted to grow other complex biological tissues, such as neurons or heart cells, with architectures resembling those found in nature.

Raman’s lab has long focused on engineering tissues that imitate the function and complexity of those in the human body. Her group previously developed hydrogel mats designed to encourage muscle cells to grow into long, aligned fibres, and even exercised the cells using pulses of light. However, creating muscle tissue that moved predictably in more than one direction had remained a challenge.

She highlighted the natural variation in muscle orientation across the body—from the ring-like muscles in the iris and around the trachea to angled fibres in the limbs—as a key source of inspiration. The stamping method allowed the team to replicate this variety with a surprising degree of control.

To achieve this, they used high-resolution 3D printing available at MIT.nano to create stamps etched with grooves matching the width of individual muscle cells. The stamps were coated with a protein to ensure clean release from the hydrogel, avoiding damage during the process.

Once the stamp was applied and cells were added, the tissue formed rapidly. Within a day, the muscle cells settled into the grooved pattern, fused, and grew into an organised, functional muscle. When stimulated by light, the artificial muscle contracted in the intended directions—mirroring the complex behaviour of a real iris.

Although the human iris comprises smooth muscle tissue—responsible for involuntary movement—the team opted to use skeletal muscle for this study to showcase the technique’s capacity to replicate natural muscle architecture using cell types typically used in robotics.

Raman explained that although this project used high-precision facilities, the stamps themselves could be reproduced with ordinary 3D printers, making the technique broadly accessible. The team planned to explore its application in other muscle architectures and cell types and to investigate new methods for triggering motion in these engineered tissues.

The potential applications included more agile and energy-efficient robots, particularly for underwater environments. By replacing traditional rigid actuators with soft, biodegradable, muscle-powered alternatives, such machines could become more sustainable and better suited for navigating confined or dynamic environments.

The research received funding support from the U.S. Office of Naval Research, the U.S. Army Research Office, the U.S. National Science Foundation, and the U.S. National Institutes of Health. The results were published in Biomaterials Science, and the MIT team included Tamara Rossy, Laura Schwendeman, Sonika Kohli, Maheera Bawa, and Pavankumar Umashankar, in collaboration with Roi Habba, Oren Tchaicheeyan, and Ayelet Lesman from Tel Aviv University.