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An Implant That Grows as a Child Grows

An overly dilated heart valve is a not so uncommon problem. While the adults can have a prosthetic ring implanted to restrict it to normal size with a single surgery, children are not so lucky. Their heart grows with them over the years and replacing those rings requires multiple surgeries. There has been less development for devices appropriate for children because the problem is more common in adults.

Eric Feins, a surgeon at Boston Children’s Hospital, along with his colleagues and his colleagues are on a mission to fix that. The premise is how do we make a ring that has growth potential. They first used a degradable polymer. The diameter of a ring made with such a material would slowly expand as it dissolved over time. A loss in thickness also means a loss in mechanical strength, no matter what the material. Any ring with a mechanical element needed to be simple with no overlapping pieces that might catch flesh or blood. So the engineers ended up turning to the Chinese finger trap, the cheap, ageless toy tube. When you stick a finger into each end and pull, the woven fibres of the trap allow it to elongate. In the process, it narrows down and eventually snares the fingers pulling it. What was important was the ability of the material to lengthen without losing strength. Feins and his colleagues filled the tubular sleeve with a biodegradable polymer, if the core degeneration can be controlled, then the braid elongation is controllable and predictable.

Currently, that core is an FDA approved polymer, something widely used and accepted. But, conceivably, the speed with which the material breaks down could be tweaked to match the growth rate of a child’s heart. Unfortunately, there are no existing heart growth curves in humans and just when and how fast a human heart grows is not completely known.

The new tricuspid valve annuloplasty ring has so far only been demonstrated ex vivo on rat tibias and piglet hearts and the next step is to put it into a living animal. Thanks to its simplicity, biocompatibility, and proven success in the lab, Feins’ ring it could eliminate thousands of surgeries on children in the coming years.

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