April 29--Doctors at the University of Michigan have created the first 3-D printed device that can grow with an infant and disintegrate inside the body when no longer needed.
The new medical implant is called an airway splint. It's designed to help babies who suffer from a life-threatening condition called tracheobronchomalacia that causes tiny airways near the lungs to collapse.
Three children between the ages of 3 months and 16 months participated in a pilot trial of the device, described Wednesday in the journal Science Translational Medicine. Prior to the surgery they had spent much of their lives in intensive care, where they needed to be on ventilators full-time to prevent death.
But after surgeons inserted the small white device around their narrow airways about as thick as a piece of pencil lead, all three showed rapid recovery.
"Holidays are no longer spent in the hospital, the kids are no longer sedated and paralyzed," said Dr. Glenn Green, associate professor of pediatric otolaryngology at C.S. Mott Children's Hospital in Michigan and one of the senior authors on the study.
"This is the first known cure of this disease," he added.
The 3-D printed airway splint looks like a small, incomplete tube with an opening that runs along the bottom. It is made of polycaprolactone, a type of polyester that is known to safely disintegrate in the body after three years, give or take six months.
The device goes outside the collapsed part of the airway. During surgery, tiny sutures are used to attach the walls of the compromised airway to the device.
"It is kind of like a tent pole system," said Dr. Robert Morrison, a head and neck surgery resident at the University of Michigan who worked on the trial.
To create the individual splints, the researchers used CT scans to make a digital model of the patient's collapsed airways. Then a custom computer program designed the splint based on the patient's specific anatomy.
"We used laser light to transform dust into a medical device that changes how the body develops," Green said. "It would have been inconceivable when I was a resident."
Even before printing out the device, the researchers take the digitally rendered splint and fit it on the digital model of the patient's airways. This allows them to test how the splint will work in the present as well as in the future as the baby's trachea grows and strengthens.
"The device is designed to have flexibility as the airways grow," said Scott Hollister, a professor of biomedical engineering at the University of Michigan who engineered the device. "As it grows radially it will press upon the splint and the splint will give way."
(Confused? Try grasping your left wrist with your right hand. Now imagine that the pressure of your left wrist growing wider and thicker is pushing the gap between the fingers and thumb on your right hand wider. That's basically how the splint works.)
After the device has gone through these digital paces, it is printed with a laser-sintered 3-D printer that deposits polycaprolactone in thin layers until an exact, physical replica of the virtual model is created.
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FOR THE RECORD
An earlier version of this post incorrectly stated that the device was printed with a laser-centered printer. A laser-sintered printer was used.
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The medical team can also use 3-D printing to produce a physical model of the patient's trachea and bronchi, which allows surgeons to practice the insertion operation before actually operating on a child.
The process is both efficient and cost effective, the research team said. Each device can be printed in just a few hours and costs about $10 to produce.
Children do eventually grow out of tracheobronchomalacia. As they grow the cartilage around their airways becomes stronger, preventing further collapse.
"If the children are doing well at age 3 then we would expect them to do well for the rest of their lives," said Green. "The airway has enough structural integrity at that point."
The key, however is getting children with the most severe cases to live that long. Green said that a few of the kids who were considered for the trial died before the necessary paperwork was completed.
Plans for a clinical trial of the device with 30 patients are in the works.
In the future, the researchers said similarly flexible devices created with the help of a 3-D printer could be applied to pediatric gastrointestinal, orthopedic or cardiovascular conditions.
"With patient-specific computer design and modeling, you can create anything that you can imagine to eventually become a medical device," said Morrison.
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