Why Can A Frozen Embryo Survive 30 Years But A Regular Cell Dies?

Ice crystals are basically tiny glass daggers. They punch holes in cell walls and kill everything inside. But scientists figured out a clever trick called vitrification. They replace the water in an embryo with a special syrup (called a cryoprotectant) and freeze it SO fast that the liquid turns to glass, not ice. No spikes. No holes. Time literally stops at -196°C. Frozen for 30 years or 300 years makes no difference. Embryos at the 5-8 cell stage are tiny enough that the syrup reaches every single drop of water. A skin cell is too big. The syrup can't get to the centre in time, ice forms, and it dies. It's not the cold that kills cells. It's the ice spikes.

Sources:
• Rall & Fahy, Cryobiology 1985, original vitrification paper
• Coticchio et al., Human Reproduction Update 2020
• Mazur, Life in the Frozen State, CRC Press 2004
• ESHRE, Cryopreservation of embryos, 2023

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