Figure 4.
Presentation of results. (a) Survival with HIFU according to warming rate and exposure time. Low warming rates show worse results in the recovery of C. elegans. The experiments were always done with plates containing groups of nematodes. These showed the following average composition: 20% individuals in stage L1, 30% in L2, 25% in L3, 15% in L4 and 10% adults. For the optimal parameters, survival by growth stages was not homogeneous, as more L1–L3 nematodes were recovered than L4 and adults. L4 survival was 70%. Adult survival was between 40 and 60%. (b) and (c) Show survival for the highest warming rates, and , as a function of exposure time. Short (less than 50 s) and excessively long (more than 70 s) exposure times resulted in very low survival rates. (d) Dependence of with the warming rate for the optimum exposure time. For low warming rates the recovery rate is close to 0%, reaching 90% for the highest warming rates. These results must be compared with the Brenner’s protocol, with only 35% for the most favorable stages (L1–L2) and close to 0% for adults. The dashed line is not an interpolation of results, but a trend line. (e) Finite element simulation of the acoustic pressure in a 2D section of the experiment. The region of highest acoustic pressure, 270 dB, is reached at the geometric focus of the transducer. (f) Simulation by finite elements of the temperature field. in a 2D section of the experiment, after 60 s of exposure to HIFU. The highest temperature is reached at the focus. The Petri dish is placed inverted, with the black rectangle representing the well containing the worms, to avoid any air gap between the ultrasounds and the nematodes. (g) Dead nematode after insufficiently rapid rewarming (). (h) Nematodes a few hours after being recovered by HIFU heating. All stages of growth are appreciated. (i) C. elegans egg after the recovery of the nematodes: their reproductive capacity is preserved after cryopreservation and HIFU rewarming.