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Human sperm remains viable in microgravity, paving the way for space colonisation

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Human sperm retains it reproductive viability even when exposed to microgravity conditions in space, a boon for possible space colonies in the future.

The study saw researchers from Dexeus Women's Health in Barcelona work with microgravity engineers from the Polytechnic University of Barcelona.

They said that the lack of difference in a range of sperm characteristics observed in frozen sperm samples exposed to microgravity and those maintained in ground conditions “open the possibility of safely transporting male gametes to space and considering the possibility of creating a human sperm bank outside Earth”.

The study builds on previous research from 2017 which saw healthy mice being produced from mouse sperm that were held aboard the International Space Station (ISS) for nine months.

Dr Montserrat Boada, a researcher on the project, explained that, while the effects of microgravity on the cardiovascular, musculo-skeletal and central nervous systems are well known and tested in space flight, relatively little is known about the effects of different gravitational environments on human sperm and eggs.

“Some studies suggest a significant decrease in the motility of human fresh sperm samples,” she said, “but nothing has been reported on the possible effects of gravitational differences on frozen human gametes, in which state they would be transported from Earth to space.”

The study was performed using a small aerobatic training aircraft, which can provide short-duration hypogravity exposure. The plane executed a series of 20 parabolic manoeuvres, providing eight seconds of microgravity for each parabola.

Overall, ten sperm samples obtained from ten healthy donors were analysed after exposure to the different microgravities found in space and ground gravity.

The sperm analysis comprised a full range of measurements currently performed for fertility testing - concentration, motility, vitality, morphology and DNA fragmentation - and results found no difference whatsoever in any of the parameters between the microgravity space samples and the control group samples from Earth.

There was 100 per cent concordance in DNA fragmentation rate and vitality and 90 per cent concordance in sperm concentration and motility.

These minor differences, Boada added, “were probably more related to heterogeneity of the sperm sample than to the effect of exposure to different gravity conditions”.

She described this as a preliminary study and her group will now move on to validate the results and then to larger sperm samples, longer periods of microgravity and even fresh sperm.

“We do need to know,” she added. “If the number of space missions increases in the coming years, and are of longer duration, it is important to study the effects of long-term human exposure to space in order to face them. It’s not unreasonable to start thinking about the possibility of reproduction beyond the Earth.”

One reason for using frozen sperm in this study was the known effect of radiation on fresh sperm.

“Radiation impairs the quality and viability of human sperm,” Boada explained. “These effects are expected to be greater on fresh sperm than on frozen samples, which are cryopreserved in special cryostraws and transported in cryotanks. So our first step was to investigate gravity conditions and frozen sperm samples. Our best option will be to perform the experiment using real spaceflight, but access is very limited.”

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