Five young men given urethra grafts engineered from their own cells are doing well six years later, according to a study published this week in the Lancet. The boys’ own urethras had been severely damaged by illness or accidents.

“When they first came in, they had a leg bag that drains urine, and they have to carry this bag everywhere they go. It’s uncomfortable and painful. So these children were mostly sitting or bed-bound,” Dr. Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine, told NPR. “These children are now totally normal,” he says. “They’re running around and doing the things they usually do.”

Atala and collaborators took tissues samples from each patient’s bladder or urethral area and then grew the cells in culture. Researchers then used them to seed tubular scaffolds and implanted the newly formed structure into patients. The reconstructed grafts looked and functioned normally after just three months. They also continued to grow with the patients, who were ages 10 to 14 at the time of the implant.

“Typically, if you’re going to see these structures fail, they can fail early or they can fail late,” Atala told NPR. “But if you have them with this long of a follow-up, then you know they’re going to do well over time.”

According to a press release from the university;

The engineered tubes were used to replace entire segments of damaged urethra in the section that runs between the penis and the prostate (posterior section) – considered the most difficult to repair. The authors note that additional studies will be required to assess the technique in adult patients, and to assess whether the technique works on other parts of the urethra.

Atala’s team had previously shown that tissue-engineered bladders restored function over the long-term in several patients. And last week, he gave a dramatic demonstration of the future of organ replacement at the TED (Technology, Entertainment and Design) conference in Long Beach, California by printing a model kidney live onstage during his talk, using a printer that spits out cells rather than ink. The organ is still a long way from being used in patients—Atala plans to begin testing the kidneys in cats—but it shows just how easily new organs might be generated.