Mechanism of Action
As MFU is a focused ultrasound device, at certain energy levels, it produces heat over 55ºC at the focal point, which leads to thermal coagulation points (TCPs) in the target tissue. The creation of TCPs leads to a healing cascade, ending with neocollagenesis and neoelastogenesis. This healing is regulated and described as an “orchestra playing” by Reinke and Song,14 which begins immediately after the first phase of the injury and lasts for 1 to 3 days. This is the most important phase for the purpose of collagen stimulation.15,16 During this very early phase, mediators such as interleukins (IL-1 and IL-6), tumoral necrosis factor (TNF-α), and other factors (FGF-2, IGF-1, TGF-β, and VEGF) lead to the production of new collagen and elastin, as well as neovascularization within the extra cellular matrix (ECM).
The second phase of proliferation lasts for 5-10 days. Under the control of regulating cytokines (IFN-α, TGF-β), fibroblasts synthesize collagen, fibronectin, and other basic substances needed for wound healing. These represent the basis for the new connective tissue matrix, serving to close tissue gaps and to restore the mechanical strength of the wound. Subsequently, the synthesis of collagen increases throughout the wound, while the proliferation of fibroblasts declines successively, adjusting to a balance between synthesis and degradation of the ECM.17 The third phase can last from 21 days to 1 year, depending on the scar tissue.
One of the most important factors is sufficient stimulation during the first phase to have enough fibroblasts to produce organized collagen and elastin. Organized collagen formation (scar tissue) is the physiological endpoint of mammalian wound repair. There is some evidence that inflammation during the process of wound healing is directly linked to the extent of scar formation.15 First, fetal wound healing, which lacks the typical inflammatory response, is scarless until a certain age.18,19 In addition, scar formation does occur when inflammation is induced in fetal wounds.20 Also, reproductive hormones have been shown to have an influence on inflammation and the formation of scars. Studies show that low estrogen levels in mice resulted in an impaired rate of healing with excessive inflammation and scarring.15,21,22
To summarize, a TCP induces tissue coagulation and necrosis and starts the healing cascade. To achieve the desired quantity and quality of collagen, a certain amount of inflammation is needed under certain basic conditions such as the required levels of mediators, hormones, and cell migration. The aging