The research team combined acoustic waves with fluid dynamics to sort high-quality sperm from semen samples, which they hope could eventually improve IVF success in patients. The method selects sperm cells on the basis of size, shape, and DNA integrity, rather than just motility.
'Sperm preparation or selection is a key step in assisted reproduction, being performed right before fertilising the egg,' said Dr Reza Nosrati, joint senior author at Monash University in Melbourne, Australia. 'Our process aims to select better sperm within a faster time frame, so hopefully this can lead to improved outcomes in assisted reproduction.'
The study, published in the journal Lab on a Chip, described a new type of 'microfluidic chip' device designed by the researchers. Raw bull semen was loaded on to the chip and allowed to flow through a channel, while acoustic waves were applied at different frequencies. The waves directed the most favourable sperm cells to a collection chamber, while sperm with low motility or poor DNA integrity was left behind and discarded. Images taken by the researchers showed that lower quality sperm, which harboured DNA damage, had distinct physical characteristics and so were affected differently by the acoustic waves.
Lead author Dr Junyang Gai at Monash University explained: 'The acoustic forces direct and push high-quality sperm out of the mainstream, across the microchannel and isolates them in a separate outlet, leaving the general population of sperm in the raw sample.'
The device could process up to 140 sperm cells per second, and isolated 60,000 high-quality sperm in 50 minutes – roughly the same number of sperm used in IVF and ICSI procedures. As well as being high-throughput, the researchers claim their technology is roughly four times faster than existing methods of sperm selection. In addition, the research team observed a 38 percent improvement in DNA integrity and a 60 percent increase in motility in the filtered sample compared with the raw sample.
Current methods of sperm selection focus solely on motility, and have remained largely unchanged since the advent of IVF. The authors noted that these methods are often labour-intensive and time-consuming, and may be partly responsible for low IVF success rates.
Although IVF success depends on multiple factors other than sperm quality, the researchers hope their approach could go some way towards treating infertility.
Dr Nosrati concluded: 'We hope that with further testing, our "acoustofluidic" sperm selection process can provide new opportunities and be of benefit to the assisted reproduction industry, and help remove the fear, anxiety and negative stereotypes associated with infertility.'