There are two different methods of embryo culture as below:

Open System: Embryo culture is performed in an in-vitro or a plate and a culture medium directly exposes to the environment inside an incubator.
Closed System: Embryos are placed in microdroplets of culture media covered by the culture oil.

Benefits of Closed System:
1. The culture oil can protect droplets of culture media from pathogen and microorganism floating inside the incubator.
2. Prevent fluid evaporation of a medium droplet
3. Slow down the CO2 diffusion from culture media
4. Increase the stabilization of temperature, pH and osmolarity
5. Absorb some lipid-soluble toxins that may include in culture media

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Reference: Prime Fertility Center Co., Ltd.