Biological Characteristics And Mechanism Of Collagen Remodeling Induced By Fractional Photothermolysis

Fractional photothermolysis (FP) as a new concept is generallyconsidered to be an effective and low-risk option for the repair of mostphotodamaged tissue. In contrast to traditional laser resurfacing, FP treatsfractions of the skin instead of the entire area of the skin. Typical side effectssuch as edema, oozing, crusting, pigmentary changes and scarring areunacceptable for many patients receiving ablative skin resurfacing. Whileepidermal damage can be avoided with the use of nonablative dermalremodeling, the major drawback of this technique is limited efficacy. FPovercomes some of the problems with these two conventional modalities in adigital manner since it is based on the density of microscopic treatment zonesinstead of causing homogeneous thermal damage at a particular depth in theskin. Fractional lasers distribute microscopically small volumes of thermaldamage within the skin. The heat-induced wound healing associated withcollagen synthesis may result from different growth factor profiles. Normalwound healing includes a vigorous proliferative response during which anabundance of growth factors and cytokines are released to promote theproliferation of various cell types within the wound. In spite of clinicalsuccess and some experimental data, few in vivo studies have investigatedthe exact mechanisms involved in the different phases underlying fractional laser effects.In this paper, we conduct an in vivo study on Kun-Ming (KM) mousemodel to evaluate the collagen remodeling process and mechanism inducedby fractional photothermolysis. Firstly, we compared quantitatively thebiophysical parameters of mouse skin after fractional laser, ablative laser andnon-ablative laser treatments. Then, skin histology, fibroblast number andcollagen-genesis were studied by comparing the treatment sites and controlsites after fractional laser treatment. The last, we evaluated and comparedquantitatively the changes of vascular endothelial growth factor (VEGF),basic fibroblast growth factor (bFGF) and transforming growthfactor-β1(TGF-β1) during damage repair process after fractionalphotothermolysis.Our results demonstrated fractional photothermolysis led to markedimprovements in skin elasticity with less erythema and no barrier damage. Inskin histology, dermal layer thickness, fibroblast number and typeⅠ andⅢcollagen showed significant increases compared with their untreated controls.The efficacy of fractional photothermolysis favored the formation of typeⅠmore than type Ⅲ collagen. Additionally, we found the levels of VEGFincreased on days1and3(P<0.05, P<0.01, respectively), TGF-β1on days1,3and7(P<0.01, P<0.01, P<0.05, respectively), and bFGF on days3,7,14and21(P<0.05, P<0.01, P<0.05, P<0.05, respectively). The amount offibroblasts, typeⅠand Ⅲ collagen showed significant correlations withVEGF in the early stages, and with TGF-β1, bFGF in the whole process.The results indicated fibroblasts proliferation, collagen synthesis andremodeling were induced effectively by FP and suggested VEGF, TGF-β1,bFGF might be all involved in the skin repair and collagen remodelingprocess after fractional photothermolysis.