Braided Cardiac Implant Grows with Child Heart

Based on the design of the Chinese finger trap, the biodegradable core is designed to constrain sleeve diameter at implantation, with subsequent gradual core degradation enabling both braided sleeve and overall device elongation to accommodate tissue growth.

Mathematical modeling and ex-vivo experiments in swine hearts demonstrated the predictability and tunability of the device for both disease- and patient-specific needs. A further study that used the rat tibia and the piglet heart valve as models of tissue growth demonstrated that polymer degradation enabled device expansion and growth accommodation in vivo. The researchers suggest their proof-of-concept design could also be adapted for a variety of other growth-accommodating implants throughout the body. The study was published on October 10, 2017, in Nature Biomedical Engineering.

“Medical implants and devices are rarely designed with children in mind, and as a result, they almost never accommodate growth,” said co-senior author Professor Pedro del Nido, MD, chief of cardiac surgery at BWH. “So, we've created an environment here where individuals with expertise and interest in medical devices can come together and collaborate towards developing materials for pediatric surgery.”

“We solved this problem of growth accommodation with a concept that already exists in nature: the octopus has a special ability to stretch its arms into confined cracks and spaces between rocks, in search of its prey,” said co-lead author Yuhan Lee, PhD, a materials researcher at BWH. “It can do this because of unique, braid-like crossfibers of connective tissue that enable the simultaneous elongation and shrinking diameter of its arms, allowing it to extend its reach two to three times beyond the original arm length.”

A Chinese finger trap is a joke toy that traps the victim's fingers in both ends of a small, cylindrical, helically wound biaxial braid, usually woven from bamboo; pulling the entire braid lengthens and narrows it by reducing the angle between the warp and weft threads at their crossing points. The more one pulls, the more the circumference shrinks, and the more the trap tightens and lengthens. Contrary to intuition, the victim of the joke must push their finger farther inside the trap for it to loosen.

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