Soft robotic heart sleeve helps pump blood
Heart failure is a multi-billion-dollar problem that affects 41 million people worldwide. While numerous promising studies, including novel therapies involving 3D printing and bionic heart patches, have been conducted to treat this condition, a commercially viable solution remains out of reach. Could a soft-robotic implant that mimics the natural motion of the heart bring us closer to one?
Since the time of Leonardo da Vinci, the heart's rotational motion has intrigued scientists. Many have tried to create models emulating it but success has been elusive. The problem lies in replicating the way the heart twists as it beats. In a motion similar to how one would wring water out of a wet towel, the top and bottom of the organ twist in opposite directions when it empties itself out. When one has cardiac failure, this ventricular twist is lost, making it hard for the other organs in the body to get the blood and oxygen they need.
Replicating this twisting motion has long been a challenge but advances in soft robotics have enabled a team of researchers from Harvard University and Boston Children's Hospital to develop a soft robotic sleeve that closely replicates normal heart muscle behavior.
The silicon-based apparatus that lead author Ellen Roche (a biomedical engineer and former Harvard doctoral candidate) has designed with her team offers several advantages over current ventricular devices (VADs).
By twisting and compressing in synch with a beating heart, it is able to augment the contraction mechanics of the failing heart muscle, a significant development that could advance the creation of better cardiac devices. Additionally, one of the challenges of using conventional mechanical devices to act as muscles lies in their rigidity as well as tendency to heat up, making it dangerous to place them near the heart. The robotic sleeve, on the other hand, uses air-powered soft pneumatic actuators placed around the heart to mimic the outer cardiac muscle layers. These twist and compress the sleeve in a similar motion to the beating heart.
In ex vivo experiments involving pig hearts, the researchers were able to get the device to conform to their surfaces and synchronize with their contraction mechanics. It was also able to restore normal blood flow in six living pigs that had acute cardiac arrest.
What makes the results of this study even more encouraging is the fact that the researchers were able to "fine tune" the device by selectively twisting and compressing either the right or left ventricle of the explanted pig hearts. This is important as chronic heart-failure often doesn't affect the entire organ but only a specific section. The sleeve could thus be customized for each patient by tuning the actuators to give more assistance to the side of the heart that is weaker. The pressure can also be adjusted accordingly as the patient's condition evolves.
Current ventricular assist devices (VADs) tend to go against the heart's natural curvature and disrupt its motion. Furthermore, as they are dependent on direct exposure to the blood, this could potentially lead to health complications, such as clotting and stroke. The soft robotic technology reduces these complications and enables patients to avoid the use of blood thinner medication, which can require constant monitoring or cause bleeding problems.
"The cardiac field had turned away from idea of developing heart compression instead of blood-pumping VADs due to technological limitations, but now with advancements in soft robotics it's time to turn back," says cardiothoracic surgeon Frank Pigula, who was involved in the study. "Most people with heart failure do still have some function left; one day the robotic sleeve may help their heart work well enough that their quality of life can be restored."
That said, while the results are encouraging, it is still early days for the device and more work is needed before it can be implanted in the body on a long-term basis. These include developing better ways to attach the device to the heart. In the studies, the researchers used a combination of a suction device, sutures and a gel interface to help with friction between the heart and the device, which was tethered to an external pump. Long-term animal studies will also need to be conducted to assess the durability of the device as well as any chronic complications that may arise.
With that said, the results of the study also pave the way for the device to be used in other applications involving soft tissue.
"This work represents an exciting proof of concept result for this soft robot, demonstrating that it can safely interact with soft tissue and lead to improvements in cardiac function," says co-author Conor Walsh, an associate professor of engineering and applied sciences at the Wyss Institute. "We envision many other future applications where such devices can deliver mechanotherapy both inside and outside of the body."
The study was published in Science Translational Medicine.
Source: Harvard University