Effect of low-intensity ultrasound on the colonization of spermatogonial stem cells

Background: Low-level-intensity ultrasound waves contribute to the proliferation, differentiation, and increasing the number of cells in vitro. However, the interaction of ultrasonic waves involving thermal effects, mechanical vibration, or cavitation as a cell proliferation factor has not been determined. Therefore, the aim of this study was to investigate the effect of cavitation (mechanical index) on spermatogonial stem cell proliferation and colonization by removing heat effects caused by ultrasound radiation. Isolated spermatogonial stem cells from neonatal mice were cultured in a DMEM culture medium with 10% FBS. Spermatogonial stem cells were stimulated by low-level ultrasound for five days and colonization and viability were evaluated on the 7 th day. Results: : Regarding the low intensity of ultrasound, the Rayleigh integral model was used for acoustic pressure computation. According to the results of modeling, the intensities of 0.28, 0.45, 0.96, and 1.34 W/cm 2 were selected at 0.5 cm of distance with the mechanical indices of 0.40, 0.51, 0.75, and 0.89. The mechanical indices of 0.40 and 0.89 resulted in 93±4 and 32±4 colonies, respectively. An increase in colony diameter was observed for the mechanical index of 0.40 during all days of the culture. In the culture on the 7 th day, it had the largest average colony diameter of 134.05±1.22 μm in comparison with other groups (p<0.05). Cell viability did not significantly differ across groups (p=0.08). Conclusion: The results suggest that a low-intensity ultrasound of 40 kHz with a 0.40 mechanical index can be effective in increasing the proliferation and colonization of spermatogonial stem cells during culture. In other words, a mechanical index within the threshold of cavitation increases the proliferation and colonization of spermatogonial stem cells.