The Fascination of Technology Bioactuators Enable Small Robots to Jump, Swim, Walk, and Grasp Objects

Related Vendors

ETH Zürich

FAULHABER Drive Systems

SIMTOS (Seoul International Machine Tool Show)

In our “Fascination with Technology” section, we showcase impressive research and development projects for design engineers every week. Today: How muscle actuators deform enough to enable small robots to jump, swim, walk, and grasp objects.

Although skeletal muscle tissue grown in the lab can contract, until now it has often done so only to such a small extent that the movement is barely visible. This poses a problem for biohybrid robots designed to move using living muscles. Researchers at ETH Zurich have now co-engineered living muscle tissue with a hydrogel scaffold. In experiments, the actuators—which are about 1.5 centimeters (0.59 inches) long—moved significantly more vigorously than earlier systems with a comparable amount of muscle. They can deform so much that the movement is visible to the naked eye. The researchers report a range of motion up to eleven times greater than in earlier systems with a comparable amount of muscle. “With previous systems, you sometimes had to look under a microscope to detect the deformation,” says Aiste Balciunaite, a doctoral student at the Soft Robotics Lab led by ETH Professor Robert Katzschmann.

Scaffold Created Using a Light-Based 3D Printing Process

The actuator consists of cultured skeletal muscle tissue derived from mouse cells and a soft, water-rich hydrogel. The muscle tissue contracts in response to electrical stimuli. The hydrogel supports it and translates the contraction into movement of the robot. According to ETH, the key was not to first build a muscle actuator and then insert it into a structure. Instead, the researchers optimized the arrangement of the muscle tissue and the shape of the scaffold together on a computer. The scaffold was manufactured using a light-based 3D printing process. Fine grooves in its surface help anchor the muscle tissue and align the muscle fibers. This is intended to transfer the tissue’s force to the structure as effectively as possible. This approach is thus similar to structural system optimization: the properties of the actuator and the geometry of the surrounding structure are coordinated with one another, rather than being developed independently of each other.

Bioactuator Jumps 5 mm high

The newly developed bioactuators can jump, swim, move across the ground, and grasp objects. Balciunaite was most impressed by the jumping. She noted that this is a rather unusual movement and requires a particularly strong deformation. This experiment in particular demonstrates how important the interaction between the living muscle and the soft artificial scaffold is. With a single contraction, the actuator lifts itself about five millimeters (0.20 inches) off the bottom of the dish, which corresponds to one-third of its body length. A walking version travels 6.2 millimeters per second (0.24 inches per second), making it faster relative to its body length than any previously known running biohybrid robot.
The fact that these small robots can move so vigorously is not due solely to the muscle tissue. The key is that the muscle and the scaffold form a continuous, firm connection. Fine grooves in the scaffold help the tissue anchor itself firmly and align its muscle fibers. This ensures that as little muscle force as possible is lost when it is transferred to the scaffold.

A Long Road from the Lab to Practical Application

However, for now, these biohybrid robots depend on a nutrient solution in which their muscle tissue can survive. The researchers are still a long way from developing a robot that can be used over the long term. ETH Professor Robert Katzschmann explains that larger systems require a kind of artificial blood supply: a vascular system that delivers oxygen and nutrients to the tissue and removes waste products. This is one of the biggest challenges for further development.Another challenge is the natural variability of living tissue. Unlike industrially manufactured components, the cultured muscle actuators do not all behave exactly the same way. The researchers therefore want to better understand and control how muscle tissue develops as it matures in the laboratory.