Growth-accommodating implant could change the field of pediatric surgery for the better

A medical implant that can expand internally to accommodate a child’s growth could be revolutionizing the field of pediatric surgery, according to a Massachusetts-based research team.

The device, which was designed for use in pediatric valve annuloplasty surgeries, was created by Eric N. Feins, MD, Yuhan Lee, MA, and colleagues with a goal of reducing the amount of cardiac surgeries a child might endure in their lifetime. The team’s findings were recently published in Nature: Biomedical Engineering.

Thousands of pediatric surgeries are performed each year, Feins and colleagues wrote in their study, for conditions like endocardial cushion defects, hypoplastic left heart syndrome, congenital mitral regurgitation and Ebstein’s anomaly. In many cases, medical devices are implanted during surgery to repair anatomical and morphological defects—a practice that’s effective in adults whose bodies aren’t actively developing. While doctors complete more than a thousand life-saving mitral and tricuspid heart valve surgeries in children each year, they don’t have the same options as adults when it comes to postoperative care.

Prosthetic annuloplasty rings, which are longer-term repair solutions, are commonly implanted in adults who have dilated heart valves, but the fixed-size implants aren’t feasible options for children whose valves and tissues are still growing. These fixed-size devices can’t accommodate regular internal growth in children, Feins and co-authors wrote, and will more often than not require reintervention, increased risks, further complications and higher costs for young patients.

The field saw hope when a biodegradable annuloplasty ring was developed for use in pediatric heart patients, but the device, designed to degrade over the course of several months, tends to lose its mechanical integrity over time and could fail.

“The lack of a suitable prosthetic ring that can reduce and stabilize the dilated pediatric heart valve but then allow for controlled, physiological growth is a major reason for the limited success of valve repair in children,” the authors wrote. “Successful tricuspid valve repair is achieved in only 50 percent of children with single-ventricle anatomy, and failed repair is an independent risk factor for mortality.”

Feins and his team designed a growth-accommodating device using a tubular, biaxial braided sleeve and biodegradable core. The researchers sought to develop an implant that was as effective in repairing tissue and organs as current fixed-size devices, could accommodate healthy tissue growth in children, was mechanically strong enough to withstand physiological stresses and possessed the ability to elongate and be fine-tuned.

In short, the final device bore a striking resemblance to a Chinese finger trap.

The biodegradable core of the new device constrains the sleeve’s diameter, the researchers wrote, and, while the core gradually degrades after implantation, the sleeve and overall device are able to elongate and accommodate tissue growth. The scientists used a stiff, biocompatible polymer made of natural components to create the device’s degrading core. Doctors will be able to fine-tune the timeframe of core degradation by adjusting the polymer’s composition.

“We solved this problem of growth accommodation with a concept that already exists in nature: the octopus has a special ability to stretch its armed into confined cracks and spaces between rocks,” Yuhan Lee, PhD, co-first author of the study, said in a release from Brigham and Women’s Hospital in Boston. “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.”

Feins and colleagues tested the new implant using mathematical modeling and ex vivo demonstrations with piglet heart valves. In vivo procedures were completed using rat tibias with a bone-growth model, and the researchers said the device could have countless other medical applications.

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