One baby born with a defective windpipe   now has hope of breathing normally thanks to 3-D printing technology, NPR reported. Garrett Peterson, now 18 months old, was born with tracheomalacia  , leaving him unable to breathe. The condition terrified his parents, who turned to specialist Dr. Glenn Green at the University of Michigan for a possible treatment. Along with Scott Hollister, a biomedical engineer who runs the university's 3-D printing lab, Green designed a device that can hold open Garrett's windpipe until it's strong enough to function independently. After taking a CT scan of Garrett's windpipe to make a replica of it, they made the "splint" with a 3-D printer. "It's like a protective shell that goes on the outside of the windpipe, and it allows the windpipe to be tacked to the inside of that shell to open it up directly," Green told NPR. On January 31, Garrett had his surgery. Surgeon Dr. Richard Ohye opened up Garrett's chest and saw that his windpipe had completely collapsed and one of his lungs was completely white -- a condition Ohye had only seen in dead bodies. After eight hours of surgery and careful placement of a splint on either side of Garrett's windpipe, it was time for the big test: What would happen when they let air flow through the windpipe into Garrett's lungs? Though he still remains in the hospital, Garrett has gotten stronger and needs less assistance breathing in the weeks since his surgery.  His parents are overjoyed, saying he's starting to act more interactive and alert. As Garrett grows, the splint will expand and eventually dissolve in his body as his own windpipe strengthens enough to work independently. 3-D printing technology has allowed doctors to help patients in ways that they hope will continue to grow. "We're talking about taking something like dust and converting it into body parts," Green said. "And we're able to do things that were never possible before." What does the author mainly talk about in the passage?
The introduction of 3-D printing technology by medical workers. The development of 3-D printing technology by engineers. The use of 3-D printing technology in saving a baby. The Potential of 3-D printing technology in surgery.