Scientists at the South China University of Technology in Guangzhou have developed a synthetic tissue that can repair penile injuries and restore normal erectile function in pigs. The artificial tunica albuginea, a fibrous sheath of tissue that is essential for maintaining erections, was created from polyvinyl alcohol with a curled fiber structure similar to that of the natural tissue.
It was tested on pigs with injuries to the tunica albuginea and found to restore function to a similar level as normal penile tissue. The researchers said the synthetic tissue should not be harmful to other surrounding natural penile tissues, adding the repair results were “good, though not perfect”.
This breakthrough could be a game-changer for the millions of men suffering from penile injuries and erectile dysfunction. While previous studies have focused on repairing the urethra, there has been less research on restoring damaged tunica albuginea tissue.
Tunica albuginea (TA) injuries can occur due to mechanical impact and Peyronie’s disease, a connective tissue disorder thought to occur as a result of injury during sex. About 5% of men between the ages of 40 and 70 suffer from Peyronie’s disease, in which scar tissue forms in the tunica albuginea, causing pain and a range of other effects.
Currently, clinicians can treat patients with damaged tunica albuginea tissue by using patches made from other tissues in the patient’s body combined with an extracellular matrix, but these patches can be rejected by the immune system or cause complications at the site of surgery. The ATA, on the other hand, is made from polyvinyl alcohol and has a microstructure similar to that of natural tunica albuginea, making it a more successful replacement for natural tissue.
“An ideal TA patch should comprehensively mimic natural TA tissue to reduce the sensation of foreign bodies and physical rejection. This work pursues this motivation. Additionally, most load-bearing soft tissues have aligned yet crimped fibers. This structure and the corresponding mechanical properties are critical for their physiological function. Therefore, the strategy for constructing ATA could be extended to biomimetic constructs of various materials and other load-bearing tissues, such as blood vessels, intestine, cornea, bladder, tendons, and myocardium,” Xuetao Shi, a researcher at the South China University of Technology in Guangzhou, China, and an author of the study, told ZME Science.
To address the issue of repairing damaged tunica albuginea tissue, the researchers at the South China University of Technology developed the ATA using polyvinyl alcohol, which has a curled fiber structure similar to that of the natural tissue. This allows the synthetic material to have biomechanical properties that mimic those of tunica albuginea. The researchers conducted laboratory experiments to investigate the toxicity and blood compatibility of the ATA, as it is designed to remain in the body for a long period of time. They found that it should not be harmful to other tissues.
Humans and pigs
Next, the researchers moved on to test their new synthetic tissue in an animal model — something that proved quite a bit more challenging than they initially bargained for. You see, many males in the animal kingdom have a bone in their penis, called a baculum, which is thought to support and prolong copulation. In a 2016 study, Matilda Brindle and Christopher Opie at University College London analyzed the size of bacula in nearly 2,000 species of mammal, including primates and carnivores, finding that the baculum first evolved 145–95 million years ago.
The baculum disappeared from the human lineage after our ancestors split with chimpanzees, and this may have coincided with the switch towards a more monogamous lifestyle, which is a fascinating story in its own right. Needless to say, the fact that so many mammals have a penis bone made this research particularly cumbersome.
“Rabbits and rats are commonly used experimental animals for penile defects, but their small size makes experimental manipulation more difficult and they are not easily observed after erection. The penile bone is an important influencing factor when considering large animals. Dogs, goats and monkeys have very pronounced penile bones, and the penis still does not bend significantly after constructing TA defect models, so they are not suitable as experimental animals,” Shi said.
Eventually, the researchers selected the Bama pig as the perfect animal model for testing the efficacy of the new ATA.
“Pigs are similar in size to humans and have a similar penis length, while there is no obvious penile bone, which we think is a more ideal choice,” Shi said.
After surgically implanting the ATA onto Bama miniature pigs with injuries to the tunica albuginea, the researchers found that patches made from the artificial tissue were able to restore erectile function to a level similar to that of normal penile tissue, suggesting that the patch successfully replaced the natural tissue’s function. The researchers also analyzed the effect of the ATA patches after one month and found that while the artificial tissue did not completely restore the microstructure of surrounding natural tissue, it developed fibrosis similar to that in normal tissue and was able to achieve a normal erection after the penis was injected with saline.
According to clinicians consulted by Shi, there are about 100,000 to 300,000 patients with a severe tunica albuginea injury in need of surgery worldwide each year. As the proportion of elderly people is expected to grow, so will the number in dire need of such treatment.
“Although TA-related disorders are not fatal, they may lead to problems such as penile curvature, painful erections and even erectile dysfunction, which can seriously affect the quality of life of patients and may also lead to psychological aspects. We hope to provide a new treatment option that will minimize the suffering of patients,” Shi told ZME Science.
While these findings are promising, the researchers note that in penile injuries, the tunica albuginea is not the only tissue that is often damaged. Nerves and the corpus cavernosum may also be damaged, making repairs more difficult. Therefore, the researchers plan to focus on the repair of overall penile defects or the construction of an artificial penis from a holistic perspective in future studies. A similar technique may be used to repair other sensitive tissues, including those in the heart and bladder.
Before the ATA is introduced to operating rooms in hospitals across the world, the synthetic tissue needs to pass a number of validation steps. First and foremost, the researchers need to guarantee that the material will work long-term, meaning it should remain stable even after 3 to 5 years of use. In the meantime, the researchers say they are constantly tweaking and improving both the tissue and the surgical technique.