It is theoretically possible to grow artificial penises in the laboratory and implant them in humans. Twelve male rabbits with “grafted” artificial penises tried to mate with females, eight of them ejaculated, and four of them produced offspring. One day in 2008, at the Wake Forest Institute for Regenerative Medicine (WFIRM) in North Carolina, Anthony Atala and his colleagues gathered to do something strange: stand in front of the rabbit’s breeding box. Observe whether male and female rabbits can mate. The suspense is soon revealed, and the two rabbits successfully become entangled. This unusual event in biology may not mean much to the average person, but to Atala it certainly meant a great deal – it proved an important breakthrough in the work Atala had been doing since 1992: it was theoretically possible to grow artificial penises in the laboratory and implant them in humans. The 12 male rabbits with “grafted” artificial penises all tried to mate with females, eight of them ejaculated, and four of them produced offspring. The medical community was understandably excited when the results were announced. The significance of this achievement is not only that it provides an additional technique for constructing artificial penises, but also that it meets the needs of many men today who have lost their external genitalia due to genetic reasons, trauma or cancer. Currently, there are two methods of treating men with defective genitalia: one is to use tissue cells to encapsulate a penile prosthesis, thereby restoring the man’s sexual function, and the other is to use organ transplants to “replace” the patient’s penis with a new one. The drawbacks of these two methods are obvious: in the case of the former, the prosthesis is a semi-rigid material, which keeps the penis in the same state, making it impossible to hide and causing embarrassment. In the latter case, the transplantation of the organ is often associated with rejection and a series of risks that can even be life-threatening. Although the new method developed by Atala’s team also relies on a donor, unlike organ transplants, this donated penis is not directly transplanted into the patient. Before that, the penis from the donor is “bathed” in an enzyme solution that sheds the donor’s cells, leaving only a collagenous skeleton. The smooth muscle and endothelial cells are then taken from the patient and implanted into the skeleton. As the cells grow, a complete penile structure developed from the patient’s cells is obtained. At this point, these penises can be transplanted into the patient. “We envision it like removing the occupants of a building along with the furniture and admitting new occupants to move in.” Atala explains it this way. Attempts to build an artificial penis using this method have made promising progress. So far, Atala’s team has successfully constructed six artificial penises and they are ready to be transplanted into recipients. However at the moment Atala says they are not ready to do so, they are testing the safety and effectiveness of these artificial penises through experiments. They need to prove that they are strong enough to survive the “wear and tear” of everyday life, and they also need to show that they can successfully achieve an erection when pumped with fluid. “We have a strict testing schedule,” says Atala, “and we still need to wait for FDA approval to make sure everything is okay before the first human trials.” However, Atala is well aware that they are currently far from conducting the first human trials – they have only indicated that such trials could begin within five years. Their main goal at the moment is to use this technology to replace some of the tissue in damaged penises for organ repair. In the short term, Atala’s goal is to make small-scale repairs to penises that are not functioning properly. Degradation of the erectile function of the corpus cavernosum is a major cause of erectile dysfunction in the penis of middle-aged and older men, according to Tom Lue, a urologist at the University of California, San Francisco. Middle-aged and older diseases such as high blood pressure and diabetes can cause damage to the penile tissue and break blood vessels, which in turn prevents the corpus cavernosum from filling with blood, ultimately leading to erectile dysfunction. If this damaged spongy tissue can be replaced, then they can regain their erectile ability. The long-term goal of Atala is to restore erectile capacity by reconstructing the corpus cavernosum. Some patients with rectal or prostate cancer may lose their ability to have an erection as a result of surgery because of damage to the nerves and blood vessels that regulate erections. If this tissue can be replaced and the damaged nerves and blood vessels reconnected, it is possible to restore their ability to have sex. Directly connecting the nerves and blood vessels via microscopic manipulation, while possible, is often not effective. Currently, a team led by Lu is trying to reconnect blood vessels and nerves in penile tissue by injecting stem cells. It is believed that their findings will also provide an important reference for Atala’s future clinical trials. But for today at least, Atala has good reason to be uncontrollably excited about his discovery, and he’s certainly not the only one.