Optimizing ultrasound dosimetry for bone fracture healing: unveiling cellular response mechanisms

Low-intensity pulsed ultrasound is approved by the FDA and NICE as an adjunct treatment for non-union bone fractures, but efficacy is not always demonstrated, suggesting that optimal conditions may not yet be established. To address this, in-vitro studies have investigated how ultrasound parameters, including intensity, duty cycle, and frequency, influence cell behavior. Despite these efforts, there is considerable variation in the reported outcomes, and the optimal combination of parameters required for achieving therapeutic effects remains undefined. We previously demonstrated that standing waves present in conventional culture ware can significantly alter the overall ultrasound dosage experienced by cells during in-vitro studies, potentially contributing to variability in experimental outcomes. This study investigates the influence of pulsed ultrasound stimulation on cellular responses to mechanical stimuli and cytoskeletal dynamics in a controlled manner. Pulsed ultrasound was investigated at peak-to-peak pressures ranging from 160 to 180 kPa, examining actin cytoskeleton and vinculin expression, which are key regulators of focal adhesions formation and cytoskeletal organization both of which are essential for bone repair. An increase in the expression of both actin filaments and vinculin was observed at 160 kPa. This pressure notably enhanced cellular responses in osteoblast-like cells compared to controls, confirming the beneficial role of ultrasound as a non-invasive treatment option for non-union fractures. Future investigation is necessary to elucidate the cellular pathways involved as a route to further optimization of low-intensity pulsed ultrasound treatments for non-union fractures.