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The eggs and sperm are manipulated using fine glass pipettes, made of thin capillary tubing, which are even finer than a human hair. These are custom made, the injection pipette being designed to hold a single sperm. Live sperm are placed in a drop of viscous polyvinyl pyrrolidone (PVP) solution, which serves to slow down the activity of the sperm. (It is helpful to slow down the sperm, so that they can be picked up more easily by the injecting needle.) A single sperm is then selected and its tail is pinched or broken to immobilize it. This is usually done by crushing the sperm tail by rolling it between the injection pipette and the base of the petri dish. It is essential to immobilize the sperm, so that it cannot move after it has been injected into the egg. Sucking it into the injection pipette then picks up a single immobile sperm.
The egg is secured in place by applying gentle suction to its shell (the zona) with a holding pipette. The sperm is then injected directly into the center (cytoplasm) of the egg by moving the injection pipette very precisely with the help of the micromanipulator into the egg, and then blowing the sperm out very gently into the cytoplasm of the egg. In order to do this, it is important to breach the zona and the outer membrane of the egg. The skill of the embryologist is a critical factor in the success of the ICSI process. After injecting the sperm, the pipette is withdrawn. Remarkably, once the injecting pipette is withdrawn, the egg will close and assume its original shape within 60 seconds. One can visualize ICSI as the sperm being given a "piggyback" ride into the egg, so that what the sperm cannot accomplish on its own, the laboratory embryologist does for it! The only requirement for ICSI is that the sperm should be alive, and there should be as many sperm as there are eggs.
Fig 1. A view of the micromanipulator
Fig 2. A single sperm is being injected into an egg during an ICSI procedure
© Dr. Aniruddha Malpani and Dr. Anjali Malpani www.drmalpani.com
Credits: How to Have a Baby: Overcoming Infertility
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