Researchers develop bio-inspired actuated material that mimics complex motion of heart muscle

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 Harvards Wyss Institute for Biologically Inspired Engineering and Harvards 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 its the materials 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."

Whats 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.

To mimic those muscles fibers, the team first developed a modified pneumatic artificial muscle (PAM), made entirely from soft material -- silicone elastomer with embedded braided mesh -- and attached via tubing to an air supply. Upon pressurization, PAMs shorten, like biological muscles, but in one direction only.

The team then embedded several of these artificial muscles within a matrix made of the same soft silicone elastomer. By changing their orientation and configuration within the matrix and applying pressure, they were able to achieve various motions in more than one direction, mimicking the complex motion of the heart.

They calculated the force and strain values for an array of PAM arrangements and used them to develop a new computer model that simulates their associated movement patterns in 3D.



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