Engineers design bionic ‘coronary heart’ for testing prosthetic valves, different cardiac units.
Because the geriatric inhabitants is predicted to balloon within the coming decade, so too will charges of coronary heart illness in the USA. The demand for prosthetic coronary heart valves and different cardiac units — a market that’s valued at greater than $5 billion immediately — is predicted to rise by virtually 13 p.c within the subsequent six years.
Prosthetic valves are designed to imitate an actual, wholesome coronary heart valve in serving to to flow into blood by means of the physique. Nonetheless, lots of them have points reminiscent of leakage across the valve, and engineers working to enhance these designs should check them repeatedly, first in easy benchtop simulators, then in animal topics, earlier than reaching human trials — an arduous and costly course of.
Now engineers at MIT and elsewhere have developed a bionic “coronary heart” that gives a extra real looking mannequin for testing out synthetic valves and different cardiac units.
The system is an actual organic coronary heart whose robust muscle tissue has been changed with a delicate robotic matrix of synthetic coronary heart muscle tissues, resembling bubble wrap. The orientation of the substitute muscle tissues mimics the sample of the guts’s pure muscle fibers, in such a manner that when the researchers remotely inflate the bubbles, they act collectively to squeeze and twist the interior coronary heart, just like the way in which an actual, entire coronary heart beats and pumps blood.
With this new design, which they name a “biorobotic hybrid coronary heart,” the researchers envision that system designers and engineers might iterate and fine-tune designs extra rapidly by testing on the biohybrid coronary heart, considerably lowering the price of cardiac system growth.
“Regulatory testing of cardiac units requires many fatigue checks and animal checks,” says Ellen Roche, assistant professor of mechanical engineering at MIT. “[The new device] might realistically symbolize what occurs in an actual coronary heart, to scale back the quantity of animal testing or iterate the design extra rapidly.”
Roche and her colleagues have printed their leads to the journal Science Robotics. Her co-authors are lead creator and MIT graduate scholar Clara Park, together with Yiling Fan, Gregor Hager, Hyunwoo Yuk, Manisha Singh, Allison Rojas, and Xuanhe Zhao at MIT, together with collaborators from Nanyang Know-how College, the Royal School of Surgeons in Dublin, Boston’s Kids’s Hospital, Harvard Medical College, and Massachusetts Common Hospital (MGH).
“Mechanics of the guts”
Earlier than coming to MIT, Roche labored briefly within the biomedical business, serving to to check cardiac units on synthetic coronary heart fashions within the lab.
“On the time I didn’t really feel any of those benchtop setups had been consultant of each the anatomy and the physiological biomechanics of the guts,” Roche recollects. “There was an unmet want by way of system testing.”
In separate analysis as a part of her doctoral work at Harvard College, she developed a delicate, robotic, implantable sleeve, designed to wrap round an entire, reside coronary heart, to assist it pump blood in sufferers affected by coronary heart failure.
At MIT, she and Park puzzled if they might mix the 2 analysis avenues, to develop a hybrid coronary heart: a coronary heart that’s made partly of chemically preserved, explanted coronary heart tissue and partly of soppy synthetic actuators that assist the guts pump blood. Such a mannequin, they proposed, needs to be a extra real looking and sturdy surroundings wherein to check cardiac units, in contrast with fashions which are both fully synthetic however don’t seize the guts’s advanced anatomy, or are produced from an actual explanted coronary heart, requiring extremely managed circumstances to maintain the tissue alive.
The staff briefly thought of wrapping an entire, explanted coronary heart in a delicate robotic sleeve, just like Roche’s earlier work, however realized the guts’s outer muscle tissue, the myocardium, rapidly stiffened when faraway from the physique. Any robotic contraction by the sleeve would fail to translate sufficiently to the guts inside.
As an alternative, the staff appeared for methods to design a delicate robotic matrix to exchange the guts’s pure muscle tissue, in each materials and performance. They determined to check out their thought first on the guts’s left ventricle, one in every of 4 chambers within the coronary heart, which pumps blood to the remainder of the physique, whereas the precise ventricle makes use of much less power to pump blood to the lungs.
“The left ventricle is the more durable one to recreate given its increased working pressures, and we like to start out with the laborious challenges,” Roche says.
The guts, unfurled
The guts usually pumps blood by squeezing and twisting, a fancy mixture of motions that could be a results of the alignment of muscle fibers alongside the outer myocardium that covers every of the guts’s ventricles. The staff deliberate to manufacture a matrix of synthetic muscle tissues resembling inflatable bubbles, aligned within the orientations of the pure cardiac muscle. However copying these patterns by finding out a ventricle’s three-dimensional geometry proved extraordinarily difficult.
They ultimately got here throughout the helical ventricular myocardial band concept, the concept that cardiac muscle is basically a big helical band that wraps round every of the guts’s ventricles. This concept remains to be a topic of debate by some researchers, however Roche and her colleagues took it as inspiration for his or her design. As an alternative of making an attempt to repeat the left ventricle’s muscle fiber orientation from a 3D perspective, the staff determined to take away the ventricle’s outer muscle tissue and unwrap it to type an extended, flat band — a geometry that needs to be far simpler to recreate. On this case, they used the cardiac tissue from an explanted pig coronary heart.
In collaboration with co-lead creator Chris Nguyen at MGH, the researchers used diffusion tensor imaging, a complicated approach that usually tracks how water flows by means of white matter within the mind, to map the microscopic fiber orientations of a left ventricle’s unfurled, two-dimensional muscle band. They then fabricated a matrix of synthetic muscle fibers produced from skinny air tubes, every related to a collection of inflatable pockets, or bubbles, the orientation of which they patterned after the imaged muscle fibers.
The delicate matrix consists of two layers of silicone, with a water-soluble layer between them to forestall the layers from sticking, in addition to two layers of laser-cut paper, which ensures that the bubbles inflate in a particular orientation.
The researchers additionally developed a brand new kind of bioadhesive to attach the bubble wrap to the ventricle’s actual, intracardiac tissue. Whereas adhesives exist for bonding organic tissues to one another, and for supplies like silicone to one another, the staff realized few delicate adhesives do an satisfactory job of gluing collectively organic tissue with artificial supplies, silicone particularly.
So Roche collaborated with Zhao, affiliate professor of mechanical engineering at MIT, who focuses on growing hydrogel-based adhesives. The brand new adhesive, named TissueSil, was made by functionalizing silicone in a chemical cross-linking course of, to bond with parts in coronary heart tissue. The consequence was a viscous liquid that the researchers brushed onto the delicate robotic matrix. Additionally they brushed the glue onto a brand new explanted pig coronary heart that had its left ventricle eliminated however its endocardial buildings preserved. After they wrapped the substitute muscle matrix round this tissue, the 2 bonded tightly.
Lastly, the researchers positioned the whole hybrid coronary heart in a mildew that they’d beforehand solid of the unique, entire coronary heart, and crammed the mildew with silicone to encase the hybrid coronary heart in a uniform protecting — a step that produced a type just like an actual coronary heart and ensured that the robotic bubble wrap match snugly round the actual ventricle.
“That manner, you don’t lose transmission of movement from the artificial muscle to the organic tissue,” Roche says.
When the researchers pumped air into the bubble wrap at frequencies resembling a naturally beating coronary heart, and imaged the bionic coronary heart’s response, it contracted in a way just like the way in which an actual coronary heart strikes to pump blood by means of the physique.
Finally, the researchers hope to make use of the bionic coronary heart as a sensible surroundings to assist designers check cardiac units reminiscent of prosthetic coronary heart valves.
“Think about affected person earlier than cardiac system implantation might have their coronary heart scanned, after which clinicians might tune the system to carry out optimally within the affected person properly earlier than the surgical procedure,” says Nyugen. “Additionally, with additional tissue engineering, we might probably see the biorobotic hybrid coronary heart be used as a synthetic coronary heart — a really wanted potential resolution given the worldwide coronary heart failure epidemic the place thousands and thousands of persons are on the mercy of a aggressive coronary heart transplant checklist.”
This analysis was supported partly by the Nationwide Science Basis.