Ice formation and its elimination in cryopreservation of oocytes.

Damage from ice and potential toxicity of ice-inhibiting cryoprotective agents (CPAs) are key issues in assisted reproduction of humans, domestic and research animals, and endangered species using cryopreserved oocytes and embryos. The nature of ice formed in bovine oocytes (similar in size to oocytes of humans and most other mammals) after rapid cooling and during rapid warming was examined using synchrotron-based time-resolved x-ray diffraction. Using cooling rates, warming rates and CPA concentrations of current practice, oocytes show no ice after cooling but always develop large ice fractions-consistent with crystallization of most free water-during warming, so most ice-related damage must occur during warming.

Ice formation and its elimination in cryopreservation of oocytes.

Damage from ice and potential toxicity of ice-inhibiting cryoprotective agents (CPAs) are key issues in assisted reproduction of humans, domestic and research animals, and endangered species using cryopreserved oocytes and embryos. The nature of ice formed in bovine oocytes (similar in size to oocytes of humans and most other mammals) after rapid cooling and during rapid warming were examined using synchrotron-based time-resolved x-ray diffraction. Using cooling rates, warming rates and CPA concentrations of current practice, oocytes show no ice after cooling but always develop large ice fractions - consistent with crystallization of most free water - during warming, so most ice-related damage must occur during warming.

Ice formation and its elimination in cryopreservation of bovine oocytes.

Unlabelled: Damage from ice and potential toxicity of ice-inhibiting cryoprotective agents (CPAs) are key issues in assisted reproduction using cryopreserved oocytes and embryos. We use synchrotron-based time-resolved x-ray diffraction and tools from protein cryocrystallography to characterize ice formation within bovine oocytes after cooling at rates between ∼1000 °C/min and ∼600,000°C /min and during warming at rates between 20,000 and 150,000 °C /min. Maximum crystalline ice diffraction intensity, maximum ice volume, and maximum ice grain size are always observed during warming.