When you think of a beating heart, you probably just picture it flexing in and out, sort of like a rubber ball being squeezed by an invisible hand. In fact, though, its motion is more similar to that of a dish rag being wrung out, with the top of the organ twisting in a clockwise direction while the bottom contracts counterclockwise. It's known as the left ventricular twist, and scientists have now replicated it using artificial muscles. The research could lead to better-functioning cardiac implants, among other things.
The scientists, from Harvard's Wyss Institute for Biologically Inspired Engineering and Harvard's School of Engineering and Applied Sciences, started with what is known as a pneumatic artificial muscle (PAM). Modeled after the striated muscle fibers found in the heart, it was made from silicone elastomer embedded with braided mesh, hooked up to an air tube.
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When air was pumped into the PAM, it responded by twisting and thus becoming shorter. This is similar to the natural fibers, which also contract by twisting and shortening.
Several of the PAMs were then embedded within a matrix of the same elastomer from which they were made. Through a process of manipulating their orientation to one another, along with selectively applying different amounts of pressure to different ones, the researchers were able to get some of the PAMs twisting in one direction, at the same time that others twisted in the opposite direction. As a result, the silicone matrix exhibited the same three-dimensional twisting motion as the heart.
The application that immediately comes to mind is one of implanted devices that could assist or even replace a faulty heart. Additionally, however, by disabling certain PAMs, it was possible to replicate the change in motion caused by heart disorders. This could prove useful in models, used to develop treatments for such conditions.
A paper on the research was recently published in the journal Advanced Materials. One of the twisting PAM-equipped prototypes can be seen in action, in the video below.