Air actuators pump real heart cavities to test cardiac devices
The device is a real biological heart whose tough muscle tissue has been replaced with a soft robotic matrix of air-inflatable actuators acting as artificial heart muscles. The orientation of the artificial muscles mimics the pattern of the heart’s natural muscle fibers in such a way that when the researchers remotely inflate the actuators, they act together to squeeze and twist the inner heart, similar to the way a real, whole heart beats and pumps blood.
With this new design described as a “biorobotic hybrid heart,” the researchers envision that device designers and engineers could iterate and fine-tune designs more quickly by testing on the biohybrid heart, significantly reducing the cost of cardiac device development.
“Regulatory testing of cardiac devices requires many fatigue tests and animal tests,” explains Ellen Roche, assistant professor of mechanical engineering at MIT. “The new device could realistically represent what happens in a real heart, to reduce the amount of animal testing or iterate the design more quickly.”
The experiments, published in the Science Robotics journal under the title “An organosynthetic dynamic heart model with enhanced biomimicry guided by cardiac diffusion tensor imaging” describes how the biorobotic hybrid heart uses organic intracardiac structures preserved from an explanted heart while replacing the cardiac myofiber architecture with air-controlled actuators that mimic the cardiac motion of the left ventricle.
The research stemmed from a previously developed soft, robotic, implantable sleeve originally designed to wrap around a whole live heart to help it pump blood in patients suffering from heart failure. The sleeve couldn’t work on a whole explanted heart due to the rapidly stiffening heart outer muscle, hence the idea to replace the latter altogether, only keeping the original intracardiac tissue.
In order to better replicate the intricate orientation patterns of the natural cardiac muscle fibres, the researchers unwraped the ventricle’s outer muscle tissue to form a long, two-dimensional muscle band whose muscle fibres orientations they analyzed using diffusion tensor imaging. They then fabricated a matrix of artificial muscle fibres made from thin air tubes, each connected to a series of inflatable pockets, or bubbles, the orientation of which they patterned after the imaged muscle fibers.
The soft matrix consists of two layers of silicone, with a water-soluble layer between them to prevent the layers from sticking, as well as two layers of laser-cut paper, which ensures that the bubbles inflate in a specific orientation. The researchers also developed a new type of bioadhesive to glue the bubble wrap to the ventricle’s real, intracardiac tissue. The new adhesive, called TissueSil, was made by functionalizing silicone in a chemical cross-linking process, to bond with components in heart tissue. The result was a viscous liquid that the researchers brushed onto the soft robotic matrix. They also brushed the glue onto a new explanted pig heart that had its left ventricle removed but its endocardial structures preserved. When they wrapped the artificial muscle matrix around this tissue, the two bonded tightly.
Finally, the researchers placed the entire hybrid heart in a mold that they had previously cast of the original, whole heart, and filled the mold with silicone to encase the hybrid heart in a uniform covering — a step that produced a form similar to a real heart and ensured that the robotic bubble wrap fit snugly around the real ventricle.
When pumping air into the bubble wrap at frequencies resembling a naturally beating heart, the bionic heart contracted in a manner similar to the way a real heart moves to pump blood through the body.
“Imagine that a patient before cardiac device implantation could have their heart scanned, and then clinicians could tune the device to perform optimally in the patient well before the surgery,” says co-lead author Chris Nguyen from the Cardiovascular Research Center, Massachusetts General Hospital. “Also, with further tissue engineering, we could potentially see the biorobotic hybrid heart be used as an artificial heart, a very needed potential solution given the global heart failure epidemic where millions of people are at the mercy of a competitive heart transplant list.”
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