3D printing isn’t new to medicine. It has been used to create everything from hearing aids to dental implants. But so far, applying this technology to children who are still growing has been a challenge. That might soon change, however, as researchers were able to cure three babies of a life-threatening breathing condition thanks to a 3D-printed splint installed on their airways. And, remarkably, the device was able to grow with them — a tremendous step forward for those who always imagined that 3D printing would save lives.

"This is the first 3D-printed implant specifically designed to change shape over time to allow for a child's growth before finally resorbing as the disease is cured," said Glenn Green, a pediatrician at the University of Michigan and a co-author of the study published today in Science Translational Medicine, at a press conference. Moreover, he said, the first child to receive this implant three years ago appears to be cured.

All three babies involved in this study suffered from a life-threatening version of tracheal bronchomalacia — a rare disease that causes excessive airway collapse during breathing. The condition affects about one in 2,000 children around the world. Typically, children outgrow the condition by the age of three, but in severe cases, children die before their airways become strong enough. This was the situation faced by the three babies in this study. All had been in intensive care units for months and had episodes that required repeated resuscitations. In fact, the only reason these babies were allowed to participate in this study is because they were in such bad shape — the airway splint was considered a therapy of last resort.

"One child was unable to have any food in his stomach due to his fragility," Green told The Verge in an email. Without the surgery, "they would have died within days to weeks."

In the study, the researchers designed splints for each of these children out of a porous, harmless material called polycaprolactone, which degrades over time. The splints are designed to be sutured to the outside of the airway, which helps hold the airway open.

Morrison et al. Science Translation Medicine (2015)

To create the splints, the researchers first created computerized 3D models of their tracheas from C.T. images. Then, they put these measurements into a custom computer program capable of automatically generating a splint design tailored to each patient’s anatomy. "We can then take the design from that program and digitally fit it back onto the patient's airway model as really a first quality measure of how the splint will work and fit to the patient's airway," explains Scott Hollister, a biomedical engineer at the University of Michigan and a co-author of the study.

When it came time to print the implants, the researchers used "laser sintering" — a process by which a machine melts a powder on a layer-by-layer basis to make a 3D structure. Printing each implant took between one and three days, the researchers say. Once that was done, the scientists ran a battery of tests on the devices to ensure that it had the right stiffness. And because the cost of the splints was so low — the material costs about $10 per splint — the researchers were able to practice installing them multiple times on 3D models of the children’s tracheas and bronchi before performing the surgeries on the infants.

Morrison et al. Science Translation Medicine (2015)

Because the splints form of a semi-circle, the researchers predicted that they would be able to expand as the children developed. The material used to make the splints would also help with that because it starts out stiff and becomes more flexible over time.

"Long-term, our greatest concern was whether the airway splint would open up as we designed it to," says Robert Morrison, a surgeon at the University of Michigan and a third co-author of the study. "If it did not, the child's airway could be prevented from growing normally and there could be narrowing of the airway, which would be as serious of an issue as their original condition."

All three surgeries were a success. Repeated CAT scans of the children months after the surgery revealed that the airways were growing properly. Today, the three toddlers have airways that have remained open — including the child who received the implant first, three years ago. Moreover, the splints have successfully degraded over time. "This airway splint cured the children of an imminently lethal disease and now is dissolving," Green told The Verge. As the splints break down, the children will excrete them from their bodies; each child should be splint-free three to four years after surgery.

Now that this study is complete, the researchers plan to conduct a trial involving children who suffer from a slightly less severe form of tracheal bronchomalacia. The researchers are also actively looking for other opportunities to use this technology. "The possibilities are really limitless," Morrison said. "When we talk about 3D printing and medicine, we talk about how you really need to switch how you even think about approaching these conditions." Green agrees. "This is the first of many devices of its kind."

Correction: A previous version of this article referred to the 3D printing technique as "laser centering." That's incorrect. The technique is called "laser sintering." We regret the error.