Robotic Picking Up of Polar Body for Biopsy: Localization and Approach

Polar body biopsy has been widely applied in the preimplantation genetic diagnosis and oocyte screen for assisted reproductive technology. The key step in the polar body biopsy is picking up the polar body using a micropipette. However, the almost transparent appearance of the polar body and its dynamic motion with the micropipette moving inside the oocyte makes it a challenging task to pick up the polar body. In this paper, a defocus imaging method is proposed to locate the polar body with an almost transparent appearance. Then, the dynamic drift of the polar body with the micropipette moving inside the cell is analyzed to determine a trajectory of the micropipette suitable for picking up the polar body. Finally, a PID-based motion control of the micropipette is developed to move the micropipette tip along the above trajectory to approach the polar body. The experimental results on porcine oocytes show that the success rate of polar body localization based on defocus imaging technology reaches 90%. Moving along the determined trajectory inside the oocyte, the micropipette is capable of approaching the polar body with an average error less than 5 μm, success rate can reach 90% (18/20), paving the solid ground for robotic picking up of the polar body.