An Automatic System for Manipulation and Rotation of Early Stage 2-Cell Mouse Embryos

Micromanipulation of biological cells such as embryos during preimplantation genetic diagnosis (PGD) requires delicate handling of cells. Specifically, accurate control of the embryo orientation is essential to gain a more favourable position for zona breaching and blastomere biopsy, ensuring embryo survival. Manual embryo reorientation is achieved by aspirating and releasing the embryo arbitrarily using a vacuum-equipped micropipette until the embryo reorients itself in a favourable manner. Unfortunately, this trial and error approach heavily relies on the operator’s skill, ultimately reducing biopsy success rates due to reduced precision in reorientation and ablation. In this study, an automatic image-based feedback orientation controller for early-stage embryos, using conventional IVF lab equipment, is proposed to automate the process of cell reorientation. Rotation of the embryo is achieved by rolling the embryo using a micropipette which grasps the embryo but allows slippage to permit the embryo to roll while in contact with a glass slide substrate. The substrate is mounted on a variable speed x,y stage which is controlled using one of two image-based rotation controllers investigated. The proposed control algorithms estimate the angular velocity of the embryo to determine the rotation angle, creating an error signal when differenced from the reference angle to drive a PID controller that changes the speed of the substrate. The first proposed controller uses the optical flow of the image feed to detect the cell rotation event and uses the kinematic model of the setup to determine the rotation angle. The second proposed controller uses the optical flow as a feedback signal in real-time to estimate the embryo rotation angle. Experimental results with both proposed controllers demonstrate accurate reorientation of the blastomeres, to lay the first steps towards a fully automated cell manipulation system.