Fig. 3: Development of an elastomer case used for slow cell freezing.

a A photograph for slow freezing of solutions using EPDM elastomer or paper towel wrapping in −80 °C freezer. Label 1, 6 mm EPDM elastomer case; label 2, paper towel; label 3, 10 mm EPDM elastomer case; label 4, without case and wrapping. b A typical plot of decreasing rate in the temperature of the solution in tubes of the 6 mm EPDM elastomer case (blue), the 10 mm elastomer case (red), paper towels with ~10 mm thickness (black), or without wrapping (gray) at −80 °C. A green dot line indicates 0 °C. The orange shade indicates the temperature range exhibiting nearly linear cooling rates. Arrows indicate the time points at which freezing starts and the linear cooling phase begins. c Summary of durations during which the temperature changed from the freezing point to the linear cooling phase (durations between two arrows in Fig. 3b). One-way ANOVA and Tukey’s test. ***P < 0.001. NS indicates not significant. N = 5 for no wrapping, N = 10 for paper towel wrapping, N = 7 for 6 mm EPDM elastomer, N = 5 for 10 mm EPDM elastomer. Average values are shown as boxes, and bars indicate standard deviation. d Summary of cooling rates in the nearly linear temperature range. One-way ANOVA and Tukey’s test. ***P < 0.001. NS indicates not significant. N = 5 for no wrapping, N = 10 for paper towel wrapping, N = 7 for 6 mm EPDM elastomer, N = 5 for 10 mm EPDM elastomer. Average values are shown as boxes, and bars indicate standard deviation.