CONICET | Buscador de Institutos y Recursos Humanos

In vitro fertilization (IVF) techniques allow to fertilize an oocyte in artificial conditions to obtain a viable embryo. IVF has changed the reality of millions of infertile couples in the last 4 decades, with more than 7 million babies born thank to these techniques. Besides, they are also widely used in the production of animals of commercial interest. However, IVFs techniques only have a 35% of efficiency in obtaining born babies. One of the main problems relies in the particularities of the sperm physiology. After ejaculation, spermatozoa are not able to fertilize the oocyte. First, they must complete a maturation process called "capacitation", that could be achieve under proper in vitro culture conditions. However, in mammal, capacitation is not synchronized in all spermatozoa and at any given time, only a small subpopulation of is capacitated (e.g., 10% in human). Few techniques have been developed to select only capacitated sperm based on physiological parameter. For instance, the Sperm Selection Assay (SSA) is a selection method based on a sperm orientation mechanism were only the capacitated spermatozoa can follow an attractant molecule concentration gradient (chemotaxis) accumulating them in the attractant compartment. However, the SSA only achieves an enrichment of the sperm suspension with capacitated sperm (3 to 4 times). Due to the large size of the cell?s compartments (mm to cm), the SSA chamber, fails to handle the no capacitated sperm which randomly ?reaches? to the well containing the attractant solution. Despite this, the use of an enriched suspension improves the embryo quality obtained by IVF in bovine, supporting the importance of the use of highly concentrated capacitated sperm suspension on IVF. Hence, how microfluidic devices can help to improve the sperm capacitated selection? In a shallow chamber ( 20 m of deep), sperm movement is limited by the top and bottom surfaces of the device. However, they move alternating forward progressive trajectories with large circular paths. But, when they reach the border of the chamber (or a lateral wall) the sperm path is modified and continues swimming next to the wall, following the chamber boundaries independently of sperm physiological status. This ?wall-driven? movement was observed in other micro-swimmers with different propulsion systems however, spermatozoa presents some particularities. Since, they move forward without sudden changes in their trajectory, when they reach the wall, the sperm velocity drops proportionally to the incidence angle and then is partially restore. Besides, sperm swimming next to the wall tend to be trapped in corners with angles lowers than 90. This sperm behaviour was accurately simulated with a simple phenomenological computational model and tuned with parameters experimentally obtained. This allow us to have a tool for optimizing sperm selection chambers designs. Then, we combined sperm ?wall-driven? movement chamber designs with sperm chemotaxis toward a physiological attractant, in order to separate capacitated and non-capacitated sperm. Preliminary results suggest that a proper chamber design combined with chemotaxis may improve the capacitated sperm separation, which in turn may improve the IVF efficiency.