Advances in tissue bioengineering have enabled lab-grown bladders, tracheas, cardiac patches and now penis parts.

Researchers from Wake Forest Institute for Regenerative Medicine at Wake Forest University in Winston–Salem, N.C., have engineered full animal replacement corpora cavernosas, the columns of tissue that fill with blood during an erection, for rabbits—in what they called "the most complete functional replacement of erectile tissue reported to date," in a paper published Monday in the Proceedings of the National Academy of Sciences.

Because the sponge-like tissue is so rare, attempts to surgically repair damaged organs have been challenging and have often called upon artificial materials such as silicon. It is the frequent lack of tissue that "currently prevents us from restoring sexual function to these patients," Anthony Atala, director of the Institute for Regenerative Medicine and chair of the Department of Urology and co-author of the study, said in a prepared statement.

In an effort to solve that dilemma, he and the Wake Forest team have devised a method to grow new smooth muscle and endothelial cells—from erectile material harvested from each individual—with which they seeded a collagen matrix for implantation (in the experimental rabbits).

Twelve male rabbits had both of their corpora cavernosas surgically removed from their penises and then replaced with the cell-seeded scaffolds. A control group had their corpora cavernosas replaced with un-seeded scaffolds.

As soon as one month after the procedure, male rabbits with repaired corpora cavernosas—and those with the unseeded scaffolds—were introduced to females. Most control rabbits without the bioengineered tissue avoided copulation, but all of the reinvigorated rabbits tried mating with the females within 60 seconds, the authors report. Of the 12 mating males, eight achieved ejaculation (evaluated via vaginal swabs of the females) and four had impregnated their partners. None of the control rabbits produced ejaculation-positive swabs.

"These results are encouraging," Atala, who in 2006 was among the researchers to report the first successful transplant of laboratory-grown organs (bladders), said in a prepared statement. "They indicate the possibility of using laboratory-engineered tissue in men who require reconstructive procedures."

Other procedures can partially restore function to a damaged phallus, and Atala's team has previously shown they could replace a small portion of the tissue (they had up to a 50 percent success rate in rabbits). But this is the first time full corpus cavernosas have been successfully replaced, the authors stated.

The researchers acknowledge that the procedure is not yet ready for prime-time—human application, but they plan to continue research to that end.

"Our hope is that patients with congenital abnormalities, penile cancer, traumatic injury and some cases of erectile dysfunction will benefit from this technology in the future," Atala said in a prepared statement. Indeed, perhaps many of these patients will some day be able to breed, if not like rabbits, then at least like average men.

Image of rabbits not used in the experiment courtesy of iStockphoto/GlobalIP