The University of Michigan's sperm sorter consists of a penny-size silicon chip divided into two channels. Semen is dripped onto one side, a saline solution on the other. Where the channels meet, the healthy, or motile, sperm swim over to the saline channel, leaving the dead or slow sperm behind. The healthy sperm are then collected for in vitro fertilization. University of Michigan scientists have developed a new technique to sort out the swimmers from the duds in semen, which could lead to a more efficient way for men who suffer from low sperm counts to make babies.
Current methods use centrifugation, which spins the sperm at very high speed. But the technique isn't efficient because live sperm are pelted with dead ones, causing a significant number of viable sperm to die in the separation. "We can harvest motile sperm from samples where there is a low number without causing any damage to the sperm," said team member Dr. Gary Smith, associate professor of obstetrics and gynecology at the University of Michigan Health System.
In men with healthy sperm counts, each ejaculation contains about 200 million to 400 million sperm. For these men, in vitro fertilization using centrifugal separation is relatively easy because it only takes 10 million to 20 million motile sperm to fertilize an egg in a petri dish. But men with low sperm counts have had less success. "For men with very low sperm count, these other techniques are often unable to recover any motile sperm," said Shuichi Takayama, assistant professor in the Biomedical Engineering program at the University of Michigan, where the new sorter is being developed. Other methods to pinpoint live sperm in a low sperm sample require a microscope and a lot of patience. The new sperm sorter may put an end to this laborious hand sorting. "It may mean that instead of having a well-trained technician, you could have one that is not so well-trained," said Dr. Mark Surrey, of the Southern California Reproductive Center in Beverly Hills.
So far the sorter has fared well in trials. In one test the team used a sample in which only 44 percent of the sperm was motile. After going through the sorter, the count of motile sperm went up to 98 percent. The sorter employs microfluidics, a branch of physics and biotechnology that examines the microscopic flow of fluids. Within the device everything is pushed downstream by gravity and surface tension. The Michigan team notes, however, that more tests are needed before the sorter becomes a mainstay in doctors' offices. Smith said he expects it will be ready for clinical use in one to two years.
