Patients' urethras functioned normally within a few weeks after surgery and maintained that function for up to six years.

CNN: Scientists 'seed' cells, make new organs

Patients had their engineered urethras implanted between March 2004 and July 2007 at the Federico Gomez Children's Hospital in Mexico City.

CNN: Scientists 'seed' cells, make new organs

In a small pilot study, published Monday in the Lancet, scientists reported successfully reconstructing urethras in five young patients, using their own cells.

CNN: Scientists 'seed' cells, make new organs

Earlier this year, regenerative medicine scientists at Wake Forest University School of Medicine reported that they had engineered five urethras between March 2004 and July 2007.

CNN: Lab-made organ implanted for first time

And that is where engineering urethras may offer some benefit.

CNN: Scientists 'seed' cells, make new organs

Their urethras continued to function after several years' follow-up.

CNN: Scientists 'seed' cells, make new organs

"Unfortunately for the narrow structures in the body (like urethras), they are kind of complex because they tend to collapse, " said Atala, who added that conventional urethra replacement fails more than half the time.

CNN: Scientists 'seed' cells, make new organs