Effects Of Laser Parameters On Biophysical Properties, Histology And Collagen Metabolism Of KM Mouse Skin

Skin rejuvenation is an important area in the medicine. Compared to traditional methods for wrinkle reduction, laser non-ablative rejuvenation can improve aged structural changes in skin without damage of the epidermis, so it becomes a major topic of interest in the aesthetic medicine. Though the effectiveness of laser nonablative treament has been confirmed in the clinic, but the results are somewhat less than entirely satisfactory. The reason may be that the mechanism underlying the non-ablative treatment is unclear, which leads to the blindness of clinical treatments. Facing the problems mentioned above, we studied the effects of 595-nm pulsed dye, 1064-nm Q-Switched Nd:YAG and 1320-nm Nd:YAG laser irradiation on skin biophysical properties, histology, type I and type III collagen by using an animal model. We aspired to reveal the link between laser-tissue effect and collagen synthesis and discuss the primary mechanism of laser nonablative rejuvenation.The main results are as follows:1. Established the animal model for the study of laser non-ablative rejuvenation. KM mice are inexpensive, easy to feed, available in large numbers and convenient for the long-term research. Our results demonstrated the KM mice denuded enabled us not only conduct noninvasive biophysical test but also perform histo-pathological and molecular studies at any moment. Moreover, this animal model has been acceptted by the domestic and foreign specialists.2. In vivo experimental study of the 595-nm pulsed dye, 1064-nm Q-Switched Nd:YAG and 1320-nm Nd:YAG laser nonablative rejuvenation to discuss the mechanism of laser nonablative rejuvenation at the histological and cellular level. The results demonstrated all three lasers had the capacity to improve the structure and fuction of mouse skin and accelerate fibroblast proliferation and new collagen synthesis. It was found that the degree of histological improvement and the increase of collgen synthesis produced by laser irradiation were related to the laser fluences applied.3. It was the first to make the measurement of biophysical properties as one of the methods for evaluation of nonablative rejuvenation and compared the effects of 595-nm, 1064-nm and 1320-nm laser on the biophysical properties of KM mouse skin. The 1064-nm laser was more effective in increasing skin elasticity, while the 1320-nm laser was better in enhancing skin barrier function and increasing skin hydration. This result showed that every laser has its merit, so optimized treatment might be performed according to patients'requirements.4. Compared the effects of 595-nm, 1064-nm and 1320-nm laser on histology, dermal thickness and collagen content of mouse skin. The 1064-nm laser induced more increase of fibroblast number, dermal thickness and collagen fibers than the other two lasers. Moreover, the collagen content in the irradiated areas of the 1064-nm laser was also superior to the other two lasers. The results showed the 1064-nm laser was more effective in improving skin structure and stimulating collagen synthesis. All three laser treatments led to the increase of dermal thickness. In addition, marked collagen synthesis was observed according to hydroxyproline content assay. Therefore, the increase of dermal thickness mainly depended on collagen synthsis and remodeling.5. Revealed the possible link between laser-tissue reactions and collagen synthesis. The 1064-nm laser resulted in more increase of collagen type III than the 595-nm and 1320-nm lasers, while the 595-nm and 1320-nm lasers induced more increase of collagen type I. It was apparent that the photomechanical reaction was helpful to synthesize collagen type III while the photo-thermal effect was in favor of the formation of type I collagen.6. In this study, several methods, including biophysical measurement, histology, sirius red technique and hydroxylproline content analysis, were together used to evaluate skin changes after laser irradiation, which made it possible to compare the efficiency of laser nonablative rejuvenation scientifically; three laser irradiation were performed on the same mouse so that the errors caused by different individuals disappeared; skin hydration, dermal thickness and hydroxyproline content were quite different in the control areas of three lasers, showing the discrepancy of sites. We used a protocol that combined every laser treatment with a control on each side of the spine at the same level. This decreased the spatial error of different sites.We believe that our in vivo experiments have clinical relevance and may provide scientific guidances for clinical treatments. Moreover,our work established a basis for further understanding of the molecular mechanisms of laser rejuvenation.