One of the first effects that we notice as we move away from the Earth is that gravity decreases. Several studies have proved that weightlessness affects cellular and molecular structures and the cardiovascular, musculoskeletal, nervous and endocrine systems, but its impact on germ cells, such as sperm and eggs, and human reproduction remains mostly unknown. A group of researchers from Dexeus Dona in Barcelona, a pioneering centre for assisted reproductive technology in Spain, in collaboration with engineers from the Universitat Politècnica de Catalunya · BarcelonaTech (UPC), has conducted a study to investigate the impact of microgravity on the motility and vitality of frozen sperm by analysing several samples exposed to short-duration hypogravity in parabolic manoeuvres. The results, which were presented in late June at the 35th Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) held in Vienna, revealed that microgravity does not affect the viability of frozen human sperm, since there were no significant differences in concentration, motility, vitality and DNA fragmentation parameters between the microgravity samples and the control group on Earth.

“This is just a preliminary study, which is part of a wider project aimed at studying the viability of human gametes in microgravity conditions more thoroughly”, explained Dr Montserrat Boada, who is leading this research. “Previous tests on animal models and fresh human sperm samples suggested a significant decrease in sperm motility. Additionally, last year NASA announced that they would launch a study along the same lines called Micro-11 to investigate the effects of microgravity at the International Space Station, but they haven’t published any results so far. This is the first study of the impact of microgravity on frozen human sperm samples”, added Dr Boada.

The researchers obtained 10 sperm samples from 10 healthy donors. Each sample was split into two fractions: one to perform the study in microgravity conditions and a control one. All of them were frozen in liquid nitrogen at −196ºC and stored until the day of the experiment. The space fractions were inserted in a tank designed for air transport inside a plane (CAP-10B) from the Barcelona-Sabadell Aeroclub that is specialised in aerobatic flights for scientific studies.

The plane executed a series of 20 parabolic manoeuvres to expose the samples to short-duration microgravity conditions (8 seconds for each parabola) using the free-fall technique. “This manoeuvre produces conditions of weightlessness that are totally comparable to those that occur in space flights and that are experienced by an astronaut in orbit”, explained the researcher Antoni Pérez-Poch, who has participated in the study as an expert in microgravity from the UPC’s Multimedia Applications and ICTs Laboratory and a professor at the Barcelona East School of Engineering (EEBE). “Technically, we never reach zero gravity because of atmospheric vibrations and friction; that is why we call it microgravity or hypogravity”, added Pérez-Poch.

After executing these manoeuvres, the sperm samples were thawed and analysed to check whether temporary exposure to microgravity conditions had had any impact on their function and parameters in comparison with the control group fractions, which were then thawed and analysed too. The analysis comprised a full range of measurements normally performed for fertility testing: concentration, motility, vitality, morphology, apoptosis and DNA fragmentation.

The results revealed that there were no significant differences in any of these parameters between the microgravity samples and the control group from Earth: “There was 100% concordance in DNA fragmentation rate and vitality, 90% concordance in sperm concentration and motility, in accordance with the standards established by the World Health Organization, and 80% concordance in morphology”, explained Dr Boada. “These minor differences are probably more related to the heterogeneity of the sperm samples than to the effect of exposure to microgravity conditions”, she added.

Dr Boada described this study as just a first step in a wider project that aims to confirm these results by conducting new experiments with more samples and longer exposure to microgravity. “We started with sperm because there was no legal restriction to using it in our study. Our project also aims to analyse the effects of microgravity on oocytes and embryos, but first we will have to seek permission from the Spanish Commission for Assisted Human Reproduction”, she added. “These results open the door to safely transporting sperm into space and creating human semen banks outside our planet”.

Pérez-Poch added, “The UPC has been the leader in Spain in conducting scientific studies in parabolic flights using acrobatic aircraft and we have published several works on alterations in human physiology, but this is the first study to ever obtain and publish data on frozen sperm samples exposed to microgravity conditions”. The UPC’s Multimedia Applications and ICTs Laboratory and Solidworks have developed an ad hoc flight simulator to optimise the parabolic manoeuvres of the plane. The results have been disseminated through several scientific publications.