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Ultrasound is considered a safe and non-invasive tool in regenerative medicine and has been used in the clinic for more than twenty years for applications in bone healing after the approval of the Exogen device, also known as low-intensity pulsed ultrasound (LIPUS). Beyond its effects on bone health, LIPUS has also been investigated for wound healing of soft tissues, with positive results for various cell processes including cell proliferation, migration and angiogenesis. As LIPUS has the potential to treat chronic skin wounds, we sought to evaluate the effects produced by a conventional therapeutic ultrasound device at low intensities (also considered LIPUS) on the migration capacity of mouse and human skin mesenchymal precursors (s-MPs). Cells were stimulated for 3 days (20 minutes per day) using a traditional ultrasound device with the following parameters: 100 mW/cm2 with 20% duty cycle and frequency of 3 MHz. At the parameters used, ultrasound failed to affect s-MP proliferation, with no evident changes in morphology or cell groupings, and no changes at the cytoskeletal level. Further, the migration and invasion ability of s-MPs were unaffected by the ultrasound protocol, and no major changes were detected in the gene/protein expression of ROCK1, integrin β1, laminin β1, type I collagen and transforming growth factor β1. Finally, RNA-seq analysis revealed that only 10 genes were differentially expressed after ultrasound stimulation. Among them, 5 encode for small nuclear RNAs and 2 encode for proteins belonging to the nuclear pore complex. Considering the results overall, while the viability of s-MPs was not affected by ultrasound stimulation and no changes were detected in proliferation/migration, RNA-seq analysis would suggest that s-MPs do respond to ultrasound. The use of 100 mW/cm2 intensity or conventional therapeutic ultrasound devices might not be optimal for the stimulation the properties of cell populations. Future studies should investigate the potential application of ultrasound using variations of the tested parameters., Competing Interests: The authors have declared that no competing interests exist.

Silicone is used widely for tissue augmentation in humans. However, late complications, such as delayed inflammation and capsular contracture, remain uncharacterized, despite their importance. In the present study, we aimed to determine whether mechanical and thermal damage induce capsular inflammation around a foreign body, and elucidate the biological mechanism underlying this phenomenon. We injected silicone into the subcutaneous layer of the skin of New Zealand white rabbits. The rabbits were divided into two groups: the control group received no treatment; in the experimental group, external force was applied near the injection silicone using high-intensity focused ultrasound (HIFU). Tissues near the injected silicone were harvested from both groups on Days 4, 7, and 30 after HIFU treatment for comparative analysis. Visual and histological examinations showed clearly increased inflammation in the experimental group compared with that in the control group. Furthermore, capsular tissue from the experimental group displayed markedly increased collagen production. Immunofluorescence revealed marked activation of macrophages in the early stages of inflammation (Days 4 and 7 after HIFU treatment), which decreased on Day 30. Assessment of cytokine activation showed significantly increased expression of heat shock protein (HSP)27, HSP60, HSP70, toll-like receptor (TLR)2, TLR4, and interleukin-8 in the experimental group. The expression of transforming growth factor-β1 did not increase significantly in the experimental group. In conclusion, damage to tissues around the injected silicone induced capsular inflammation. Macrophages and damage-associated molecular pattern molecules were involved in the early stages of inflammation. HSP release activated TLRs, which subsequently activated innate immunity and induced the inflammatory response., Competing Interests: The authors have declared that no competing interests exist.