New shunt could eliminate many heart surgeries

Children born with defects affecting the lower chambers of the heart undergo a series of invasive surgeries starting at a young age. The first procedure involves implanting a plastic tube called a shunt to improve blood flow. However, as the child grows, the shunt is often replaced to accommodate changes in the body. Now, researchers have designed a shunt that expands when activated by light. If the device is successfully developed, it could reduce the number of open-heart surgeries these children undergo.

The researchers will present their findings at the American Chemical Society (ACS) Fall Meeting. ACS Fall 2024 is a hybrid meeting that will be held virtually and in person from August 18-22 and will feature approximately 10,000 presentations on a range of scientific topics.

“After the surgeon places the tube, these children often have to have two or three or even four additional surgeries to implant a slightly larger tube,” said Christopher Rodell, who presented the research findings. “Our goal is to enlarge the inside of the tube using a light-emitting catheter that we insert inside the shunt, eliminating the need for additional surgeries altogether.” Rodell is an assistant professor of biomedical engineering at Drexel University.

These congenital heart defects affect the lower chambers of the organ, called the ventricles, which restricts blood flow to the lungs and other parts of the body. Without surgery, babies with these conditions cannot survive. Often born small, these infants can grow rapidly after their first shunt surgery.

To accommodate their growth, surgeons often perform additional open-heart surgery. Each time, this procedure poses a risk to the child. In a study of 360 patients who underwent the first heart reconstruction procedure, 41 required additional procedures to implant a larger shunt, and seven died as a result of the surgery.

Previously, Rodell’s colleagues at Drexel, Amy Throckmorton and Kara Spiller, had built a stretchable prototype to potentially replace the most commonly used type of shunt. To do so, they coated the inside of the tube with a hydrogel containing a network of polymers surrounded by water and connected to each other by bonds called crosslinks.

The formation of new crosslinks forces water out of the hydrogel and pushes the polymers together, which contracts the hydrogel and expands the interior of the shunt. In the initial design, the new crosslinks formed automatically, without an external trigger.

Rodell joined Throckmorton and Spiller to help them redesign the shunt so that the materials were safe for clinical use and it could be adjusted to meet the needs of each child. He accomplished this by developing new polymers for a hydrogel that would form new crosslinks and increase the inner diameter of the shunt in response to a trigger. To initiate the crosslinking on demand, Rodell decided to use blue light, because this wavelength carries enough energy to initiate the reaction but is safe for living tissue.

“Light has always been one of my favorite triggers because you can control when and where you apply it,” Rodell says.

For the new device, Rodell and his team led by graduate student Akari Seiner are using a fiber-optic catheter, essentially a long, thin tube with a light-emitting tip. To activate the light-sensitive hydrogel inside the shunt, they plan to have surgeons insert the catheter into an artery near the armpit and then maneuver it into position, eliminating the need to open the baby’s chest.

In laboratory experiments, they found that they could expand the shunt gradually, with the amount of expansion varying depending on the length of time it was exposed to light. The results indicate that once implanted, the shunt can be adjusted to suit each child. They found that they could dilate the shunt by up to 40 percent, increasing its diameter from 3.5 millimeters to 5 millimeters, almost the size of the largest shunt implanted in children.

They also evaluated the response of blood cells and blood vessels to the modified shunt. They found no evidence that the implanted tube caused blood clots, an inflammatory response or other reactions that could pose potential health problems.

The team next plans to test full-length shunt prototypes in an artificial device that mimics the human circulatory system. If those experiments are successful, the researchers plan to move on to animal models. The technology could be useful beyond single-ventricle heart disease, Rodell said. Surgeons could, for example, use similar tubes to replace blood vessels in children injured in car crashes.

“In these procedures, you have the same problem: children are not little adults, they’re still growing,” Rodell says. “That’s something we have to consider in biomaterials, how the graft will behave over time.”