What have we learned from sperm behaviour under micro-confinement conditions and how can be used to improve the in vitro fertilization techniques?

CUBILLA, MARISA A.; BETTERA MARCAT M.A.; G.L. MIÑO; A. J. BANCHIO; V. I. MARCONI; GIOJALAS, LAURA C.; A. GUIDOBALDI

Congreso; II Brazil-Argentine Microfluidics Congress; 2019

In vitro fertilization (IVF) techniques allow to fertilize an oocyte in artificial conditionsto obtain a viable embryo. IVF has changed the reality of millions of infertile couplesin 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 ofthe 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 maturationprocess called "capacitation", that could be achieve under proper in vitro culture condi-tions. However, in mammal, capacitation is not synchronized in all spermatozoa and atany given time, only a small subpopulation of is capacitated (e.g., 10% in human). Fewtechniques have been developed to select only capacitated sperm based on physiologicalparameter. For instance, the Sperm Selection Assay (SSA) is a selection method basedon a sperm orientation mechanism were only the capacitated spermatozoa can follow anattractant molecule concentration gradient (chemotaxis) accumulating them in the attrac-tant compartment. However, the SSA only achieves an enrichment of the sperm suspensionwith 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 en-riched suspension improves the embryo quality obtained by IVF in bovine, supporting theimportance 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 shallowchamber ( 20 μm of deep), sperm movement is limited by the top and bottom surfacesof the device. However, they move alternating forward progressive trajectories with largecircular paths. But, when they reach the border of the chamber (or a lateral wall) thesperm path is modified and continues swimming next to the wall, following the chamberboundaries independently of sperm physiological status. This ?wall-driven? movement wasobserved in other micro-swimmers with different propulsion systems however, spermato-zoa presents some particularities. Since, they move forward without sudden changes intheir trajectory, when they reach the wall, the sperm velocity drops proportionally to theincidence angle and then is partially restore. Besides, sperm swimming next to the wall◦ Thursday 10:05 - 10:25 Auditoriotend to be trapped in corners with angles lowers than 90 . This sperm behaviour was ac- curately simulated with a simple phenomenological computational model and tuned withII Brazil-Argentine Microfluidics Congress 43WednesdayWednesday Contributed Talks 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 ca- pacitated and non-capacitated sperm. Preliminary results suggest that a proper chamber design combined with chemotaxis may improve the capacitated sperm separation, whichin turn may improve the IVF efficiency.