Optimization of therapeutic ultrasound stimulation to increase cells´ viability and proliferation

Abstract

Objective: Therapeutic ultrasound (US) has been suggested to treat several human tissues due to its potential to promote cells´ activity. This study envisaged the establishment of an optimized US protocol to enhance cellular viability and proliferation. Methods: Human-derived cells were exposed daily or every other day to US for three days. Different central frequencies (0.45, 0.66, 1.00, 1.25, 1.50 and 2.00 MHz) and power densities (30, 100, 200 and 250 mW/cm2) were applied in continuous and pulsed mode (1 Hz, 50% duty cycle) and the temperature rise was monitored. The most promising parameters were further optimized in terms of stimulation time (5, 10 and 20 min), pulse frequency (1, 2 and 4 Hz) and duty cycle (20 and 50%). After three days, metabolic activity and proliferation were evaluated. Results: Stimulating with 250 mW/cm2 at continuous 1.25 MHz for 5 min (every other day); at pulsed 0.45 MHz (daily) or 2.00 MHz (every other day) for 20 min (1 Hz, 50% duty cycle); at pulsed 0.45 MHz (50% duty cycle, daily) or 1.25 MHz (20% duty cycle, every other day) with 2 Hz pulse frequency for 10 min displayed significantly higher proliferation and metabolic activity. These ultrasonic waves induced vibrations at cells´ surface, which activated their mechanoreceptors and intracellular mechanisms, resulting in augmented proliferation and metabolism. US stimulation did not increase the temperature during stimulation. Conclusions: Stimulating human cells with therapeutic US was efficient in increasing their viability and proliferation. These findings will improve the current knowledge of therapeutic US effectiveness.