Using tissue grown in a laboratory, researchers have engineered fully functional replacement penises. The organs were made for rabbits, but the technique may someday be useful for people.

"This technology has considerable potential for patients requiring penile construction," wrote researchers in a study published Monday in the Proceedings of the National Academy of Sciences.

Leading the team was Anthony Atala, director of Wake Forest University's Institute of Regenerative Medicine. Atala is best known for developing a technique in which cells are taken from an organ and sprayed onto a frame made of collagen, the primary structural protein in animal tissue. The structure is then bathed with growth-stimulating compounds and kept in an oven that duplicates the body's temperature and chemical composition.

Given these starting conditions, natural biology does the rest. The cells divide and arrange themselves in natural, working configurations.

Atala's group has already implanted lab-grown bladders, grown from the patients' own tissue, in seven men. Bladders are just one of dozens of organs being engineered by the group, from every part of the body — but in some organs, it's been difficult to find the right starting mix of different cell types, and reconstruction has proved challenging. The penis is one such organ.

In earlier studies, the researchers grew segments of the penis' main structures, called corpus cavernosa. These lie along the shaft of the penis, and are made from a complex, sponge-like arrangement of different cell types. But when implanted in rabbits whose corpus cavernosa had been removed, the tissue failed to become erect.

This time, they used a different mix of growth factors, and grew entire corpus cavernosa, rather than pieces of them. It worked: The next penises responded normally to electrical and chemical stimuli, and — more importantly — to biological imperative. When given the chance to have sex, eight were able to ejaculate, and four became fathers.

Oddly, the procedure seemed to make the rabbits randier than usual.

"Most control rabbits did not attempt copulation after introduction to their female partners," wrote the researchers. "All rabbits with bioengineered neocorpora attempted copulation within one minute of introduction."

Image: PNAS

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Citation: "Bioengineered corporal tissue for structural and functional restoration of the penis." By Kuo-Liang Chen, Daniel Eberli, James J. Yoo, and Anthony Atala. Proceedings of the National Academy of Sciences, Vol. 106 No. 45, November 9, 2009.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.