Different mineral oils used for embryo culture microdrop overlay differentially impact media evaporation

Abstract

Mineral oil is an important component of the embryo culture system; serving as a means to avoid media off gassing and stabilizing pH, providing temperature stability and helping avoid evaporation and harmful osmolality increases. Stability of media osmolality is especially important considering the increased use of non-humidified benchtop incubators and uninterrupted embryo culture media system. Several types of mineral oil are available for use during embryo culture, which can vary in viscosity and density. To compare different mineral oils during microdrop overlay in dry benchtop incubators and resulting impact on media evaporation. Microdrops of culture media (25ul) were prepared in a laminar flow hood by pipetting 25ul of media onto the surface of a 35mm dish and covering with 3.5ml of 1 of 4 types of mineral oil (Sigma Light Mineral Oil 0.84g/ml, Sigma Heavy Mineral Oil 0.88g/ml, OvOil™ paraffin oil and Hypure™ Heavy paraffin oil). All dishes were placed into a gassed, non-humidified benchtop incubator and cultured for 6 days. Dishes were removed and osmolality of microdrops measured using a vapor pressure osmometer (Wescor). Positive controls included media directly out of the bottle. The resulting 5 treatments were measured 3 times each. Data were analyzed using ANOVA and Tukey analysis and presented as the mean ± SEM, p<0.05. Mean osmolality of control media was 266 ± 0.88mOsm. Compared to control, evaporation and resulting significant increase in osmolality occurred in all microdrop treatments regardless of the type of oil used for overlay. However, the amount of osmolality change varied based on the type oil used. Use of Heavy Mineral Oil resulted in the least evaporation, while Light Mineral oil had the most. Both paraffin oils showed similar osmolality increases at levels between light and heavy mineral oils.Tabled 1Mineral Oil UsedOsmolality (6 days of Culture)Sigma Light Mineral Oil311 ± 2.3mOsmcSigma Heavy Mineral Oil289 ± 0.6mOsmaOvOil™ (100% pure paraffin oil)298 ± 1.2mOsmbHypure™ Heavy (paraffin oil)297 ± 1.5mOsmb Open table in a new tab Different minerals oils used for microdrop oil overlay result in different rates of media evaporation and resulting osmolality increase. Density of mineral oil seems to be an important factor to consider in terms of media evaporation. Differing nomenclature used to characterize oils used for embryo culture can be confusing and it may be beneficial for companies to list oil density as part of descriptive materials.