Mechanical characterisation at cell level
Oocytes are cells, whose sizes are big enough to allow a micro-mechanical characterisation. In our research, we study porcine oocytes with a diameter of about 140 µm. The Zona pellucida is the membrane surrounding the ooplasm, whose thickness is about 14 µm. This membrane ensures that only one sperm can penetrate the cell, to prevent polyspermy. The glycoproteins in the membrane form filaments in approximately three layers. In literature different orientations of these filaments are discussed. For a better understanding of the mechanical behaviour, the anaylsis of the filament orientation is of major interest.
One possibility to determine the orientation of filaments is a technique based on polarisation microscopy called PolScope. Further, we investigate the mechanical behaviour by oocyte indentation. The oocyte is hold by a pipette and is then compressed at a force sensor. Combining the results from the different characterisation techniques, we can provide parameters sets for a mechanical model. A Finite element framework is used to study strains and stresses of the oocytes during cell compression.
The proposed mechanical model serves us as an additional tool to support in vitro fertilization research. After a gentle testing, it may be possible to get information about healthiness and stage of maturity, to raise the rate of successful fertilizations. So the results of mechanical tests could be used as an additional source of information to prevent an implantation of unsuitable oocytes in the female organism.