The future of medicine just might include prosthetic penises that can be printed on demand. In a study out this month, scientists have demonstrated that their 3D-printed penile implant can restore sexual function in animals. Researchers from the U.S., Japan, and China conducted the study, published last week in Nature Biomedical Engineering. In experiments with both pigs and rabbits that had damaged penile tissue, their 3D-printed gel-based implant allowed the injured animals to successfully mate and reproduce as usual. The technology could lead to better functional replacements for penises as well as other organs that are rich in blood vessels, the researchers say. The teams biomimetic model of a peniss head and corpus cavernosum. Wang et al/Nature Biomedical Engineering The penis is a complex organ, thanks to the intricate network of blood vessels and tissues needed to engorge it. Scientists have historically struggled to create models in the lab that can accurately replicate the structures of vessel-rich organs like the penis, but the researchers said theyve made a major step forward with their latest work. First, they created a model of the glans, the head of the penis, and the corpus spongiosum, the spongy column of tissue along the penile shaft that surrounds the urethra and contains the blood vessels responsible for making the penis erect (blood flows into the arteries of the penis, which also presses up against the veins there, keeping the blood in place and the penis rigid). The teams model even mimicked the urethral structures found in a typical penis. Secondly, they 3D-printed a gel-based scaffold modeled after the corpus spongiosum, one designed to withstand the enlargement of a penis during sex. These implants were then transplanted into rabbits and pigs that had a partly damaged corpus spongiosum. The researchers also seeded some of their implants with endothelial cells (cells that line the blood vessels) from the animals, hoping that the fusion would improve their odds of being functional. From top to bottom: Images showing a normal pig penis; a penis with a damaged corpus cavernosum; and a pig penis repaired with the teams implant fused with endothelial cells two weeks after the transplant. Wang et al/Nature Biomedical Engineering The implants seemed to significantly improve the animals erectile function within weeks, especially when they were seeded with endothelial cells. Overall, the animals with fused implants had improved tissue regeneration and their erectile function essentially returned to normal, even allowing them to reproduce with 100% effectiveness. The fertility of the [endothelial cell] groups demonstrates the recovery of erectile function and the ability to ejaculate, suggesting the restoration of the cavernous tissue in the treated males, the researchers wrote. The results only show off a proof-of-concept for now. The scientists note that more research will be needed to develop implants capable of regenerating and restoring more severely damaged penises in humans. But they say that their model should make it easier to study erectile dysfunction, and they believe that their work can foster the creation of truly impressive replacements for the penis and similar organs. Our findings support the further development of 3D-printed blood-vessel-rich functional organs for transplantation, they wrote.