27 February 2014
Bend me, shape me... into a heart
by Will Parker
The human body has lots of soft muscular systems that bend, twist, extend, and flex in complex ways. Robotic systems that try to emulate these biological workhorses have usually fallen well short, but a team of researchers at Harvard has developed a low-cost, programmable soft actuated material which can replicate the biological motions of the heart.
Replicating the motions of a heart is tricky because 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.
"Most models of the heart used today do not mimic its 3D motion," said lead researcher Ellen Roche. "They only take flow into account." What's missing is the essential twisting motion that the heart uses to pump blood efficiently.
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. "That was a great moment," Roche said. "It means that now we have proof of concept that we can in fact mimic the heart's natural 3D motion."
"We drew our inspiration for the soft actuated material from the elegant design of the heart," added co-researcher Conor Walsh. "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."
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