Another Soft Robotics Breakthrough: Artificial muscles that do the twist

The heart circulates blood as if it were wringing a towel. The bottom twists in a counterclockwise direction while the top twists clockwise. On the right is the team’s model of the heart, showing tube-like pneumatic artificial muscles (PAMs) that mimic the heart’s striated muscle fibers. Credit: Harvard’s Wyss Institute and SEAS.

“It could inspire a whole new class of cardiac therapies, such as improved ventricular assist devices that mimic natural heart motion.”

In the heart, as in the movies, 3D action beats the 2D experience hands down.

In 3D, healthy hearts do their own version of the twist. Rather than a simple pumping action, they circulate blood as if they were wringing a towel. The bottom of the heart twists as it contracts in a counterclockwise direction while the top twists clockwise. Scientists call this the left ventricular twist—and it can be used as an indicator of heart health.

The heart is not alone. The human body is replete with examples of soft muscular systems that bend, twist, extend, and flex in complex ways. Engineers have long sought to design robotic systems with the requisite actuation systems that can perform similar tasks, but these have fallen short.

Now a team of researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering and Harvard’s School of Engineering and Applied Sciences (SEAS) has developed a low-cost, programmable soft actuated material that gives renewed hope to the mission. They demonstrated the material’s potential by using it to replicate the biological motion of the heart, and also developed a matching 3D computer model of it, as reported in Advanced Materials.

“Most models of the heart used today do not mimic its 3D motion,” said lead author Ellen Roche, an M.D./Ph.D. candidate at SEAS who is also affiliated with the Wyss Institute. “They only take flow into account.”

What’s missing is the essential twisting motion that the heart uses to pump blood efficiently.

“We drew our inspiration for the soft actuated material from the elegant design of the heart,” said Wyss Core Faculty member Conor Walsh, Ph.D., the senior author, who is also an Assistant Professor of Mechanical and Biomedical Engineering at SEAS and founder of the Harvard Biodesign Lab. “This approach could inspire better surgical training tools and implantable heart devices, and opens new possibilities in the emerging field of soft robotics for devices that assist other organs as well.”

The heart moves the way it does because of its bundles of striated muscle fibers, which are oriented spirally in the same direction and work together to effect motion.

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