Scientists Say This 'Cotton

Published on

In a novel breakthrough, scientists have invented a cost-effective technique to create heart valves in just a matter of minutes. Remarkably, these heart valves were ready to function right after being inserted into sheep.

The team of researchers has named this technique "Focused Rotary Jet Spinning," similar to a cotton candy machine backed by a hair dryer. Despite the requirement for more extensive in vivo research to evaluate the longevity of these valves, they have successfully regulated blood flow in sheep for an hour.

This pioneering prototype was just published in the journal Matter.

"The two big advantages of our method are speed and spatial fidelity," explains first author Michael Peters. "We can create really small fibers—on the nanoscale—that mimic the extracellular matrix that heart valve cells are used to living and growing inside, and we can spin full valves in a matter of minutes, in contrast to currently available technologies that can take weeks or months to make."

The composition of pulmonary heart valves consists of three semi-overlapping flaps or leaflets that fluctuate with each pulsation of the heart. These leaflets play a crucial role in ensuring unidirectional blood flow within the heart. They fully open with every heartbeat, facilitating forward flow of blood, and then completely shut to prevent any backward flow.

To create the valves, researchers use air jets to direct liquid polymer onto a frame shaped like a valve, resulting in a meshwork of microscopic fibers that is seamless.

These valves are intentionally temporary and regenerative. They offer a porous foundation that allows for cellular infiltration and accumulation. As the polymer naturally decomposes, the cells progressively take over and replace it.

"Cells operate at the nanometer scale, and 3D printing can't reach down to that level, but focused rotary jet spinning can put nanometer-scale spatial cues in there so that when cells crawl up into that scaffold, they feel like they’re in a heart valve, not a synthetic scaffold," adds senior author Kit Parker. "There's a certain trickery that's involved."

The group examined the durability, flexibility, and recurrent open-close capabilities of the valves. They employed a pulse duplicator, a device that mimics the rhythmic beating of the heart, to carry out these tests.

"A normal heart valve functions for billions of cycles throughout one's life, so they’re constantly being pulled and stretched and stimulated," adds Peters. "They need to be very elastic and retain their shape despite these mechanical stimuli, and they also have to be strong enough to withstand the back pressures from blood trying to flow backwards."

Additionally, they cultured cardiac cells on the valves to evaluate their compatibility with biological systems and to ascertain the effectiveness of cellular infiltration into the scaffold structures.

"Valves are in direct contact with blood, so we need to check that the material doesn't cause any thrombosis or obstruction of the blood vessels," adds first author Sarah Motta.

They went on to examine the immediate effectiveness of these valves in sheep, who make for an excellent animal model due to several reasons. The dynamics inside the hearts of sheep and humans are quite alike, and the sheep heart poses a challenging environment for heart valves because of the species’ fast calcium metabolism, which can increase the likelihood of calcium deposit formation, a common issue in heart valve recipients.

The team successfully implanted these valves in two sheep and assessed their positioning and performance using ultrasound for an hour. Both of the implanted valves functioned instantaneously; however, one valve in a sheep dislocated after some time, which researchers suspect was due to a size mismatch. The valve in the second sheep exhibited satisfactory performance for an hour, and a post-mortem study revealed no complications such as ruptures or blood clot formation. It was also observed that cells had already started infiltrating and sticking to the valve.

Moving forward, the team intends to conduct more extensive testing of the valve performance over prolonged periods and in a larger number of sheep.

"We want to see how well our valves function over the scale of weeks to months, and how effectively and quickly the sheep's cells and tissues are actually remodeling the scaffold," adds Peters.

"It's a long slog to develop something that's going to go into a human patient, and it should be long," adds Parker. "You have to do a lot of animals before you put something into a human."

Image Credit: Getty