It is where a machine creates a three-dimensional object -- one with height, width and depth. The machine uses plastic or a similar material to produce the object. Usually, the material is added one layer at a time, with the layering process repeated again and again until the product is ready.Now researchers in the United States have developed what they call a 4-D medical device. They say the device is designed for very young patients, and changes as their bodies grow.The researchers are with the University of Michigan in Anna Arbor. They worked with children who have a rare condition called tracheobronchomalacia, or TCM. The disease weakens the walls of the airway. The breathing passage can collapse, cutting off oxygen to the children.One of the researchers is Glenn Green. He told reporters that TBM is a rare, but very serious breathing disorder. He said the three children in this study had been in an intensive care unit at a hospital for months. Doctor Green said the three patients were given very strong drugs."During that time, to stay alive, they required heavy sedation, narcotics and even paralytics. They all had tracheostomies, where a breathing tube was placed through their necks, and were on artificial ventilators. There is no cure, and life expectancies for each of these children were grim."Patients with TBM have been treated with a splint, a support that surrounds the airway and protects it. The splint worked just like those often used to support a broken arm. But young children grow quickly. As a result, the child's airway would soon outgrow most splints.The new 3-D printed splint is designed to expand over time. Each one is specially designed and made for each patient.Over time, the airway becomes strong enough to resist collapsing. Several years after the operation, the 3-D splint is slowly removed through natural processes.Two of the children in the study were said to be much improved. A third suffered no problems, but still needs ventilating equipment to breathe, perhaps because of other issues.Doctor Green says 3-D printing can help doctors and patients alike."We actually printed (a replica of) the patient's airway, the trachea and bronchi, beforehand. By printing this ahead of time, then we were able to practice the operation before we actually incised the child just to go in and save lives."Researchers reported the findings in the journal Science Transitional Medicine. Megan Frisk works for the journal. She said the findings..."...represent not only a new surgical option for patients suffering from obstructive airway disease, but also showing a promise for 4-D printed materials in medicine."The researchers say they are planning a larger study of this device in children with TBM.更多听力请访问51voa.com