Figure 4.

To determine if cavitation is a factor in the observed reduction in C. elegans’ motility, we exposed the worms to 10 s of 500 mW 20-MHz SAW in $10\mu \ell$ droplets of either polyvinyl alcohol or M9 solutions in the chamber configuration (see Fig. 1(a,b)). Polyvinyl alcohol, as prepared, is far more viscous than the M9 buffer solution with a consequent reduction in any ability to induce cavitation. The (a) effects of the SAW on the worms’ average speed in the two solutions were statistically identical (ns, p > 0.5), whether exposed to SAW or not. For (a), significance was based upon a two-way ANOVA upon data from $N=12$ independent experiments for the control and for the SAW-exposed worms, with n = 150–200 worms tested in each experiment, defining **p < 0.002. By increasing the SAW power to 1500 mW and switching to the (b) free fluid film configuration (see Fig. 1(c)), many of the worms were found to be paralyzed after only 5 s exposure, whether in M9, PVA 5% wt, or PVA 15% wt solutions. The (c) ratio of paralyzed to total number of worms in each experiment shows that switching from the less viscous M9 to the more viscous PVA produces a significantly (**p < 0.01) greater amount of paralysis, with insignificant (ns, p > 0.5) differences in paralysis between 5% wt and 15% wt solutions of PVA. Significance was based upon a two-way ANOVA upon $N=6$ independent experiments for each of the three liquid media choices, with n = 100–150 worms tested in each experiment, where ns implies p > 0.05, *p < 0.05, and **p < 0.01. In both (a,c) experiments, the normality of the data was assessed using the Shapiro-Wilk test with *p > α = 0.05 indicating the data were normally distributed.