Doctors have successfully built and implanted a stem cell-grown windpipe into a 2 ½-year-old girl, making her the youngest person ever to receive a bioengineered organ.

The surgery, which took place on April 9, took place at Children’s Hospital of Illinois and was formally announced Tuesday, is the sixth of its kind and the first to take place in the United States.

The procedure was approved by the Food and Drug Administration in circumstances when hope of survival of the patient is otherwise limited.

The windpipe was developed and inserted by Dr. Paolo Macchiarini, a specialist in the field of regenerative medicine.

In this case, the patient, a Korean-Canadian toddler named Hannah Warren, was born without a trachea, a condition with a fatality rate of 99 percent. Since her birth she has lived in a newborn intensive care unit in a Korean hospital, breathing through a tube inserted in her mouth.

Macchiarini said Warren helped him realize that stem cell-built organs may be most successful with young children given their natural ability to grow and heal.

“Hannah’s transplant has completely changed my thinking about regenerative medicine,” he said, according to The New York Times.

He further described the look of confusion on the girl’s face when she first realized her breathing tube was gone as “beautiful.”

To make the windpipe, Macchiarini and his team created a tube of plastic fibers a half-inch diameter they then bathed in a solution containing stem cells taken from Warren’s bone marrow. It was then incubated in a shoebox-sized device called a bioreactor, according to the Times.

As of yet, scientists are not sure what happens after the windpipe is implanted; however, they believe the stem cells signal to the body to send other cells to the windpipe, though doctors estimate she will need another one in about five years.

The girl’s father said he discovered Macchiarini on the Internet shortly after the birth of his daughter.

“It actually is unbelievable,” he said, "the fact that they’re doing this, at this time, when Hannah needed it the most.”