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Avoid disrupting the Matrigel matrix layer or coating by carefully aspirating and adding medium. When aspirating the spent medium, tilt the vessel to pool the medium to one side minimizing contact with the Matrigel matrix layer. When adding medium, if possible, rest the tip along the side of the vessel and allow the liquid to slowly flow down and across the growth surface.
Cell culture medium should be changed as necessary to maintain the proper culture environment.
Below are a few resources that give guidance on general cell culture best practices: