The role of ultrasound-induced cavitation in the 'in vitro' stimulation of collagen synthesis in human fibroblasts.

Collagen synthesis by human embryonic fibroblasts in vitro was estimated using a collagenase-sensitivity assay. Collagen synthesis was stimulated by irradiation with ultrasound at a frequency of 3 MHz, a space-time peak intensity of 0.5 Wcm-2, pulsed at a mark-space ratio of 2:8 ms for 5 min at ambient pressure. This stimulation was suppressed by the application of a positive pressure of 2 atmospheres during irradiation of the cells. Increasing the pressure in the absence of ultrasound had no effect on the rate of collagen synthesis in control cells. This stimulation, therefore, appears to be due to ultrasound-induced cavitation, since it is unlikely that increasing the pressure could modify any other ultrasonic parameter. Collagen synthesis is apparently stimulated to the same extent as general protein synthesis.