Non-Ablative Laser Induced Collagen Remodeling And Non-Invasive Detection: An Experimental Study

The effectiveness of collagen remodeling induced by laser skin treatment can be attributed to the unique physical properties of laser technology. By wavelength selection, the laser can effectively target the specific chromospheres, such as melanin, oxygen-hemoglobin and water, and defines the penetration depth, which affects the extent of the laser treatment in the skin. The laser pulse duration determines the mechanism of laser-tissue interactions (photo-thermal vs. photo-mechanical effect), which may result in different repairing mechanisms once the local damage is induced by the laser treatment. The laser energy density affects the degree of specific laser effect set by the laser pulse duration. The optimal combination of those parameters may lead to the most effective collagen remodeling while minimizing side-effect during the non-ablative laser skin rejuvenation.In this paper, we conduct a comparative in vivo study on Kun-Ming (KM) mouse model to evaluate the collagen remodeling process induced by the different non-ablative laser treatment parameters: namely, the 595-nm pulsed dye laser (10 ms), 1320-nm Nd:YAG laser (0.35 ms), 1064-nm Nd:YAG lasers with long-pulsed (0.3 ms) and Q-switched (5 ns).Each modality exposed one side of the mouse dorsal skin leaving the other side as the contralateral control. Then skin histology, fibroblast number and the genesis of typeⅠa ndⅢcollagen were studied by comparing the treatment site and control site at one hour, one day, one week, three weeks, four weeks and eight weeks after laser treatment. Hydroxyproline content of the skin tissue was measured four weeks and eight weeks after laser exposure.In our study, all laser treatments led to marked improvements in dermal layer thickness, collagen fiber density and increase in fibroblast number and hydroxyproline content compared with their own controls. Collagen synthesis and remodeling induced by the Q-switched 1064-nm laser were most effective four weeks after treatment, while there was no significant difference among the other three modalities. While 1320-nm Nd:YAG laser was most effective in holding skin hydration. four weeks after the laser treatments, increase of collagen typeⅠandⅢwas respectively observed with the 595-nm (52.7±5.6% vs 24.4±2.8%), 1320-nm (48.9±3.7%vs 22.5±4.2%), 1064-nm long-pulsed (46.4±4.6%vs15.9±2.9%) and Q-switched(45.1±6.1% vs 50.3±5.4% ) lasers. We found that the efficacy of photo-mechanical effects promotes the synthesis of collagen typeⅢmore effectively, whereas the photo-thermal effect favored the formation of collagen typeⅠ. And systematical study proved that Q-switched 1064-nm Nd:YAG laser was the best in collagen remodeling.Additionally, we found confocal laser scanning micrioscopy could image the changes of the collagen before and after laser treatments clearly and measure the thickness of collagen, verifying the value of confocal laser scanning microscopy in imaging the effects of laser induced collagen remodeling.