Fig. 4: Drosophila embryos cryopreservation using joule heating.

a Images of the Drosophila embryos on the stainless steel (SS) mesh after cooling. Embryos were loaded with different ethylene glycol (EG) concentrations. b Geometry and dimensions of the SS mesh and embryos used in the heat transfer modeling. Points A, B, and C represent the top, middle and bottom of the embryo, respectively. Point D and E represent the SS mesh in contact with the embryo and outside the embryo, respectively. c Temperature profile at different locations for 1 ms joule heating. d Warming rate distribution at the middle plane of embryos. e Warming rate of the embryo for different joule heating pulse widths. f Images of embryos on the SS mesh acquired by a high-speed camera at 3000 fps. The cryoprotective agent (CPA) was 27% EG + 9% sorbitol. The voltage was 290 V. g Normalized grayscale intensity of the embryos was plotted from the high-speed camera videos. Ice (i.e., white color) showed a high intensity value. Different CPA concentrations (labelled as EG + sorbitol concentration) were tested. n = 5. Data presented as mean ± s.d. h Survival of embryos after exposure to different CPA concentrations. Hatch and adult rates represent the survival from embryos to larvae and larvae to adults, respectively. n = 4. i Temperature of the embryos after 1 ms joule heating using different voltages. j Survival of embryos after 1 ms joule heating using different voltages. The CPA was 27% EG + 9% sorbitol. n = 8. k Comparison of embryo survival using convective warming and joule heating (290 V, 1 ms) for different CPA concentrations. n = 8. For a and f, scale bar is 500 µm. For g–j, n represent independent experiments. For h, j, and k, bounds and horizontal line of box represent standard deviation and mean respectively; whiskers represent max and min. For c–e, i modeling results were shown. Multivariate analysis of variance (MANOVA) and Tukey’s post hoc were used for statistical analysis. ns, p > 0.05.