Effect of therapeutic ultrasound on the mechanical and biological properties of fibroblasts

Conventional doses of therapeutic ultrasound alter the mechanical behavior of ligament fibroblasts to improve the regenerative and remodeling stages of the wound healing process. Using a multidisciplinary approach, we applied ultrasound doses of 1.0 and 2.0 W/cm2 at 1 MHz frequency for five days on ligament fibroblasts. Atomic force microscopy showed a decrease in cell elastic modulus for both doses, but the treated cells were still viable based on flow cytometry. Finite element method analysis exhibited visible cytoskeleton displacements and decreased harmonics in treated cells. Colorimetric assay revealed increased cell proliferation, while scratch assay showed increased migration at low doses. An increase in collagen and fibronectin was detected by enzyme-linked immunoassay at high doses, and β-actin expression for both treatments was visualized through immunofluorescence imaging. Both doses of ultrasound altered the fibroblast mechanical properties due to cytoskeletal reorganization and enhanced the early and late stages of cell repair.