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.
Of the heart's three layers of muscle fibers, the outermost layer is the one most responsible for the dominant global twist so the team used their computer model to identify a PAMs configuration within a cup-shaped matrix that most closely mimicked the fibers in the outermost layer of the heart. They built the prototype and attached motion trackers to see how it would respond when the PAMs were subjected to various pressures.
Their experimental results closely matched the computer model predictions and also corresponded to the available clinical data on the action of the ventricular twist.
"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." In short, they got their model hearts to do the twist.
What's more, by selectively deactivating certain PAMs within the matrix, the
|Contact: Kristen Kusek|
Wyss Institute for Biologically Inspired Engineering at Harvard