Sperm filmed in 3D for the first time
A team of researchers from four European institutions have developed a method to record 3D movies of living sperm. This could improve the chances of success of in vitro fertilisation where assessing the health of the sperm is very important. Soon doctors may have a technique to help them sort the good sperm cells from the less viable ones.
In addition to showing the sperm's movement and behaviour in real time, the method simultaneously provides detailed 3D imaging of the sperm's form and structure to detect potential infertility-causing anomalies, such as the ‘bent tail’ that prevents the cells from swimming straight.
The researchers say this is the first technique for collecting data on sperm cell motility - a key predictor of IVF success - in three dimensions and over time. They describe their method in a paper published in The Optical Society’s (OSA) open-access journal Biomedical Optics Express.
To create the technique, the team of researchers from Italy and Belgium combined microscopy and holography to visualise live sperm. Another achievement of the project was that ‘by acquiring a video of the moving sperm in 3D, we add a fourth dimension -- time,’ explained lead author Giuseppe Di Caprio of the Institute for Microelectronics and Microsystems of the National Research Council (NRC) in Naples, Italy, and Harvard University in Cambridge, Massachusetts.
To achieve their new tracking system, the researchers first separated laser light into two beams. They transmitted one beam through a dish containing live, swimming sperm cells and then recombined it, after magnification through a microscope, with the second beam.
‘The superimposed beams generate an interference pattern that we can record on camera,’ Di Caprio explained. ‘The resulting image is a hologram containing information relative to the morphologies of the sperm and their positioning in three-dimensional space. Viewing a progressive series of these holograms in a real-time video, we can observe how the sperm move and determine if that movement is affected by any abnormalities in their shape and structure.’
Di Caprio says that the 3D imaging technique, known formally as digital holographic microscopy (DHM), yields morphology and motility data on sperm consistent with that found in previous studies, but with the unprecedented bonus of seeing cause and effect relationships between the two.
‘For example,’ Di Caprio said, ‘we found that most of the sperm cells we observed swim along in one plane as expected. However, with the more detailed analysis provided by DHM, we also were able to show that this "in-plane" movement - which we believe is linked to higher potential for fertility - does not occur when there are morphological anomalies such as sperm with misshapen heads or bent tails.’
Now that the efficiency of sperm tracking via DHM has been demonstrated, Di Caprio says that the international research team will next attempt to exploit its capabilities for defining the best-quality sperm for IVF.
The other institutions involved in this research are the National Institute of Optics of the NRC and the Center for Assisted Fertilization, both in Naples, and the Free University of Brussels in Belgium.