An engineering team from the University of Toronto discovered a human sperm's ability to tweak their swimming style to best suit their current environment. The human sperm's slithering, snake-like motion can benefit infertility treatments by adopting a new way to choose the best sperm for the job.

Six years ago, when he and his wife were having troubling conceiving, mechanical and industrial engineering professor David Sinton first studied the human sperm's movement. The couple's fertility treatment was successful but the experience was eye-opening, especially for Sinton who thought how an engineer like him could help in improving the infertility treatments.

Factors such as DNA damage, malformed tails and poor motility are few of the common human sperm defects among men who suffer from infertility. Using his knowledge in microfluidics, the study of how to manipulate fluids in tight space, Sinton and his research team created channels where they could 'race' sperms and dubbed it the "sperm Olympic marathon."

In their previous study, they found that winning sperms have higher DNA integrity which enables them to produce an embryo. The team continued their study and noticed that some of the sperms tend to hangout near the channel walls. Lead by engineering doctoral candidate Reza Nosrati, the second phase of the study began.

The researchers created a method called the total internal reflection fluorescence (TIRF) microscopy that enabled them to see what's going on 100 nanometers on a surface that is flat. Using the TIRF method, the researchers found that the sperm cells of both humans and bulls have a slithering, snake-like movement. It was the first time sperm cells were observed in 2D. The researchers noticeed that the closer the sperm cells are to the channel walls, the higher the chances they will switch to slither mode.

"When you look at the TIRF microscopy images, you see that the head is actually aligned very closely with the surface," said Nosrati. He added that when observing them in 2D, the sperms swim by at least 50 percent faster.

For the human sperm, the environment's thickness is also a factor. The harsher the environment, the more they slither, an ability that gives them a competitive advantage in the female reproductive tract.

The study was published in the Nature Communications journal on Nov. 10.

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