Last month, a woman gave birth to a baby boy after undergoing a womb transplant. Now scientists are reporting have successfully grown a human penis in a lab and are steadily approaching transplantation in the next few years.

In 2008, urological surgeon and professor of regenerative medicine Anthony Atala and his colleagues successfully attached a bioengineered penis to 12 male rabbits—all the rabbits attempted to mate, eight had ejaculated, and four produced offspring. Since then, Atala and his team at the Wake Forest Institute for Regenerative Medicine have been working hard to similarly bioengineer a penis for humans.

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Currently the only options available for trans men and men who have lost their penis through genetic defects, injury, or cancer is penis reconstruction using tissue from other parts of the body with a penile prosthetic inside or a penis transplant (although these can be risky and aren't always successful). The first man to have ever undergone a penis transplant in 2006 had it removed within two weeks for psychological reasons.

Atala's method isn't exactly growing a dick from scratch. Inspired by a technique used in biological skin dressings, he took a donor penis, and soaked it in a concoction of enzymes that would remove the donor cells. He tells The Guardian:

"You're left with a mostly collagen scaffold – a skeleton if you like, that looks and feels just like the organ," explains James Yoo, one of Atala's collaborators at the institute. "Think of it like a building. If you remove all the furniture and the people, you're still left with the main structure of the building. Then you replace the tenants with new ones. That's the whole idea. It's just that the building is a penis and the tenants are cells."

So to "repopulate" the "building" with the "new tenants," Atala would use the patient's cells taken in a biopsy and grown in culture.

Smooth muscle cells, which relax during an erection to allow the vessels to dilate and the penis to fill with blood, are first, followed by endothelial cells which line the interior surface of blood and lymphatic vessels. When ready, the bioengineered penis is ready to be transplanted to the recipient.

Atala has successfully engineered half a dozen human penises and is currently testing them for "safety and effectiveness," so that they can get the approval necessary to attempt a first in-man test.

One machine squashes, stretches and twists them to make sure they can stand up to the wear of everyday life; another pumps fluid into them to test erections. Sliced segments are tested at the genetic, cellular and physiological level.

Neither Atala nor Yoo will be pushed for a date for the first test in man, saying only that they'd expect it to occur within five years. "In the end we're aiming for the entire size of the organ," says Atala. "But in reality our first target is going to be partial replacement of the organ."

And there you have it. Yay boners!

Image via Getty.