Ultrasound found to boost motility of 'lazy' sperm

Engineering researchers at Monash University have shown that exposing ‘lazy’ human sperm to 20 seconds of ultrasound at 800 mW and 40 MHz increased measures of sperm motility (their swimming ability) by up to 266% and reduced the proportion of inactive or ‘non-progressive’ sperm from 36% to just 10%. Their study, published in the journal Science Advances, suggests a promising new treatment for asthenozoospermia — a condition where sperm have reduced ability to move, and a major cause of reduced fertility in men.

Drugs such as pentoxifylline have already been developed to increase sperm motility, but their application has been limited due to potentially harmful side effects, such as damage to sperm DNA. A recent study has shown that ultrasound can improve sperm motility in humans and bulls by boosting mitochondrial metabolism, but it’s been difficult to evaluate the effectiveness of this technique at the single-cell level.

In this latest study, researchers at Monash’s Applied Microfluidics and Bioengineering (AMB) Lab constructed a system to trap single sperm cells in microdroplets within which they could be exposed to sound waves while being examined and filmed at high speed under a microscope. Initially, 36% of sperm were graded as non-progressive (grade C), 38% slow progressive (grade B) and 26% rapid progressive (grade A).

After ultrasound exposure, only 10% of sperm remained in grade C, with 42% in grade B and 48% in grade A. Furthermore, the testing showed no detrimental effects of ultrasound on the integrity of DNA in the sperm or their viability.

“Ultrasound not only increased the swimming velocity of sperm but also promoted almost two-thirds of lower grade sperm to a higher motility grade,” said PhD candidate Ali Vafaie, lead author on the study.

“Sperm with low motility before we applied ultrasound showed the greatest increase in motility after ultrasound exposure, and we know from clinical data that even a 10% increase in sperm motility leads to an increase of 8% in pregnancy rate.”

“The ultrasound technique has tremendous potential to boost success rates in even the most challenging cases,” added Dr Reza Nosrati, Director of the AMB Lab. He said higher sperm motility allows for the use of assisted reproduction options that are less invasive, and have higher success rate with lower risks to the health of offspring.

“By making immotile sperm motile and motile sperm more motile, we can help more patients meet the minimum requirements to have conventional IVF rather than more invasive and costly options like intracytoplasmic sperm injection (ICSI), which involves injecting a single sperm into each egg using a very fine needle.”

The effects of ultrasound exposure, and particularly the consistency and duration of the improvement in motility seen in the donor samples, will now need to be tested on the sperm of men whose fertility is low due to asthenozoospermia. Commentators have also noted that, in instances where we don’t know why sperm are moving less, increasing their motility might not help with overall fertility.

“Future research should focus on clinical outcomes, such as fertilisation, blastulation and pregnancy rates, to ascertain the clinical utility of this innovative technique,” noted Associate Professor Alex Polyakov, a fertility specialist at The Royal Women’s Hospital and Medical Director of Genea Fertility Melbourne.

Image credit: iStock.com/Alexandr Mitiuc