MPU: Learning more about new (and old) forms of male contraception

I first became interested in birth control after I got a pulmonary embolism from my daily oral contraceptive in the fall of my freshman year. After that experience, I was intrigued by the effects of birth control and the various contraceptive mechanisms that were currently being researched, which was when I came across the Male Contraceptive Initiative. Having taken Mandarin since sixth grade, this project immediately appealed to me. I am currently pursuing a degree in Computational Biology and Comparative Literature with English and Chinese at Brown University, so this project was the intersection of my academic and personal interests: biology, Mandarin translation, and birth control. 

Understanding the technology

There are two vas deferens that sit behind the long muscular tube that runs from the epididymis into the pelvic cavity. The vas deferens is surrounded by the spermatic cord and transports mature sperm to the urethra before ejaculation. With some parts coiled and some parts straight, the vas deferens can be anywhere from 30 to 45 centimeters. 

The medical polyurethane elastomer (MPU) plug hopes to regulate birth control by blocking the vas deferens, causing azoospermia, an absence of sperm ejaculated. The elastomer is formed with the mixture of two solutions that form a smooth elastomer plug by chain extension. To inject this solution, the vas deferens is gripped with a vas-fixation clamp, then an eight-gauge hypodermic needle is used to puncture the vas deferens. A six-gauge blunt-ended needle is inserted and tested to ensure it is in the lumen. This procedure is repeated on both vas deferens, then procaine is released. After residual fluid has left the needle, 0.16-0.22 ml of the mixture of the two solutions is injected through the needle. The polymerization is reported to take 1-3 minutes, but requires 24 hours for complete setting. ​

History of the technology

First popularized in China in the 1990s, the intravascular injection of a medical polyurethane (MPU) plug was a highly researched form of male contraception. The procedure includes a percutaneous injection of medical polyurethane in order to plug the vas deferens. 

The idea plugging the vas deferens first populated in 1983, and in the following 10 years, 33 different embolization agents were tested in China. As the technology progressed, limitations prevented its widespread use and implementation. Notably, China served as the perfect pivot for male birth control given the relatively high receptiveness of males in China to fertility regulation. To that end, male contraception was a key aspect of many of China’s “Five-year plans.” 
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After the method was first used by Zhao Shengcai of Shanxi Provincial People’s Hospital, many modifications were made in hope to reduce the complications and toxicological complications that were associated with the procedure. The changes are listed below:

1. Finding the appropriate injection dose: If the dose was too small, the embolus formed from injection would fail to occlude the vas deferens. If the dose was too large, the vas deferens will rupture and overflow, not only failing to achieve contraception, but also causing the pain. The results of one study confirmed that the most effective embolic agent was 0.14 +/- 0.03ml, which was 10-19 times the volume of vas deferens. Zhao Sheng Cai developed a dosage metric based on the thickness of the vas deferens.. For a thicker vas deferens, 0.17 ml was suitable. For a medium vas deferens, which is most vas deferens, 0.15 is suitable. For a thinner vas deferens, 0.10 to 0.15 ml is suitable. 
2. Gentamicin was also tested as a co-infusion agent to lower the risk of complications. In 1993, Lu Yan He et. al found that gentamicin remains in the embolus due to gravity, and therefore inhibits the growth of perigastric bacteria. 

However, in 1992, despite a 96.2% sperm disappearance rate, the complication rates reported by authors were not consistent, which Chen Zhen-Wen et. al attributed to different techniques, specifically the mixing of plugging agents. Because of the toxicological concerns of the MPU plug, researchers began to test a similar method, but with silicone rubber. Ultimately, research surrounding the MPU came to a halt due to conflicting reports of complications. 

In 2010, Gu Yuqun reported that while Zhao Shengcai had reported successful results, other researchers were not able to replicate these results, marking the ultimate decline in the research and application of the MPU. The study ultimately determined that the MPU could not be used for future research due to the potential rupture of the vas deferens and the toxicity of the potential release of amines when the solution is injected into the vas deferens.