Experiments conducted at the University of Minnesota (so far only on animals), could help children with congenital defects, because they adapt to the body as it develops.
One of the most difficult challenges faced in paediatric cardiac surgery is the management of the artificial valves that are inserted into the hearts of children born with serious congenital heart defects. Surgical techniques have become very advanced and operations are carried out successfully, but the hearts of little patients then naturally grow in size, like the rest of their bodies, and so the implanted valves become inadequate and often need replacing.
Hence, in the case of more serious illnesses, children have no choice but to undergo four or five operations (sometimes even more) over the course of time, all of which are very demanding and invasive. In fact, they replace the “old” valves with others that are more suitable in terms of shape and size, until the heart stabilises, i.e from the end of adolescence onwards.
Researchers have been trying to fix this problem for many years, and now a significant response has come from the University of Minnesota, where a team of researchers led by Robert Tranquillo has developed a new type of heart valve that can grow inside the recipient organ, as they say in technical jargon.
Experiments carried out on several lambs have yielded good results (which were then published in the journal Science Translational Medicine), and the researchers intend to continue along this line, eventually leading to tests on children.
"This is a huge step forward in paediatric heart research," said Robert Tranquillo, a professor in the Department of Biomedical Engineering at the University of Minnesota, "This is the first demonstration that a valve implanted into a large animal can grow with the animal into adulthood. We have a way to go yet, but this puts us much farther down the path”.
How does the new type of valve work?
The researchers combined tissue-engineering techniques with a “basis” of regenerative medicine. In practice, to put it very simply, they grew the skin cells of a sheep in a special gelatine-like substance inside a tube-shaped microstructure (similar to a blood vessel) in the laboratory for eight weeks. They then developed and grew these tubes using a piece of equipment known as a bioreactor. Finally, using special detergents, they removed (“washed away”) all the residual sheep cells to avoid possible rejection.
“The next step”, as explained in a statement from the University of Minnesota, “was to precisely sew three of these tubes (about 16 mm in diameter) together into a closed ring. The researchers then trimmed them slightly to replicate a structure like a heart valve about 19 mm in diameter”.
This experimental valve was then implanted in the pulmonary artery of seven lambs (the pulmonary artery is connected to the right ventricle of the heart). Here is the echocardiogram after implantation: https://www.youtube.com/watch?v=rme9CZgRgsg.
Within a year, the valve had regenerated, because its matrix had been populated by cells from the recipient lamb, and its diameter had increased to that of a physiologically normal valve (25 millimetres).
The researchers also saw an increase (from 17 to 34 percent) in the length of the valve leaflets measured using ultrasound images. Finally, the researchers showed that these “tri-tube valves” worked better than those currently available, triggering fewer calcifications and blood clots. Here is a tri-tube valve created in the laboratory: https://www.youtube.com/watch?v=zpRbFsAVofA
Future developments
The next step," Tranquillo announced, "will be to implant the tri-tube valve directly into the right ventricle of the heart to emulate the most common surgical repair. If all goes well, procedures will be set up to test this technique on humans in the next few years. If we can get these valves approved someday for children, it would have such a big impact on the children who suffer from heart defects and their families. That's the dream."
