Columbia engineers design artificial muscle that makes robots stronger, more dexterous

The artificial muscle used as a bicep lifts a skeleton’s arm to a 90 degree position. Photo credit: Aslan Miriyev/Columbia Engineering.

Engineers have been challenged when it comes to creating untethered soft robots that actually function and move in a lifelike fashion.

However, researchers at Columbia Engineering in the Creative Machines lab led by Hod Lipson, professor of mechanical engineering, developed a 3D-printable synthetic soft muscle. This artificial active tissue with intrinsic expansion ability does not require an external compressor or high voltage equipment as was needed with previous muscles.

The new material has a strain density (expansion per gram) that is 15 times larger than natural muscle, and can lift 1000 times its own weight.

Previously tested materials have not stood up when it comes to functioning as a soft muscle — due the inability to exhibit the desired properties of high actuation stress and high strain.

Existing soft actuator technologies are typically based on pneumatic or hydraulic inflation of elastomer skins that expand when air or liquid is supplied to them. The external compressors and pressure-regulating equipment required for such technologies prevent miniaturization and the creation of robots that can move and work independently.

“We’ve been making great strides toward making robots minds, but robot bodies are still primitive,” said Hod Lipson. “This is a big piece of the puzzle and, like biology, the new actuator can be shaped and reshaped a thousand ways. We’ve overcome one of the final barriers to making lifelike robots.”

Soft material robotics are a new area for discovery and expanded applications. Unlike rigid robots, soft robots can replicate natural motion to provide medical and other types of assistance, perform delicate tasks, or pick up soft objects.

Aslan Miriyev, a postdoctoral researcher in the Creative Machines lab and lead author of the study, used a silicone rubber matrix with ethanol distributed throughout in micro-bubbles to achieve an actuator with high strain and high stress coupled with low density.

The solution combined the elastic properties and extreme volume change attributes of other material systems while also being easy to fabricate, low cost, and made of environmentally safe materials.

After being 3D-printed into the desired shape, the artificial muscle was electrically actuated using a thin resistive wire and low-power (8V).

The team tested the artificial muscle in a variety of robotic applications where it showed significant expansion-contraction ability, being capable of expansion up to 900% when electrically heated to 80°C. Via computer controls, the autonomous unit is capable of performing motion tasks in almost any design.

“Our soft functional material may serve as robust soft muscle, possibly revolutionizing the way that soft robotic solutions are engineered today,” said Miriyev. “It can push, pull, bend, twist, and lift weight. It’s the closest artificial material equivalent we have to a natural muscle.”

The researchers will continue to build on this development, incorporating conductive materials to replace the embedded wire, accelerating the muscle’s response time and increasing its shelf life.

The team’s long-term goal is to involve artificial intelligence to learn to control the muscle.

me.columbia.edu