Skin Penetration Of Chemical Sunscreens Based On Confocal Raman Imaging

Exposure to UV light for long time can result in sunburn,skin aging,and even skin cancer.The topical role of human use of UV filter-containing products is to avoid these risks.On the one hand,to ensure sun protection,UV absorbers should adhere to the skin surface like a protective film with a high affinity for the stratum corneum(SC).On the other hand,to ensure safety,the UV absorber should penetrate the skin as little as possible.Ideally,the stratum corneum would block as much UV filter as possible and not accumulate any amount of UV filter in the active skin.Confocal Raman spectroscopy is an effective tool for studying depth-related physiological parameters of the skin by obtaining distribution maps containing depth chemical information using confocal Raman imaging techniques,allowing real-time,non-invasive characterization of various skin parameters such as stratum corneum thickness,skin chemical component distribution and transdermal penetration of UV-filtering agents.Therefore,this thesis effectively visualizes the penetration of UV filters in the skin by characterizing the stratum corneum thickness and visually evaluating the penetration behavior of UV filters in situ and in real time by confocal Raman imaging.Two widely used UV filters were also used to evaluate the safety of sunscreens by designing two different blocking schemes.The details of the study are as follows.Part 1.In this work,the individual tissue components of the skin were first characterized by confocal Raman technique.We used the distribution of amide protein(C=O stretching,about 1653 cm-1)in skin tissues to characterize the skin by Raman imaging in depth direction.The thickness of the stratum corneum was also successfully separated with the help of two algorithms,PCA principal component analysis and K-mean clustering.Part 2.Based on the first part of the work on the thickness of the stratum corneum and the distribution of its chemical composition,the foundation for subsequent penetration studies was solidified.Therefore in this work,we took the widely used hydrophilic UV filter phenylbenzimidazole sulfonic acid(PBSA)as the target of our study,and evaluated the safety of sunscreens by designing six different new sunscreens,mainly adding six different types of thickening agents to block the penetration of UV filter,while using the thickness of the stratum corneum as one of the penetration indicators.Meanwhile,we constructed a skin mathematical model by ourselves,which can analyze the diffusion coefficient of UV filter in the skin,and successfully achieved the blocking penetration of water-soluble UV filters.Part 3.Based on the second part of the work,in this part we targeted the widely used lipophilic UV filter ethylhexyl methoxycinnamate(EHMC)as a research target.In order to achieve the blocking of oil-soluble UV filter with bioaffinity and non-toxicity,we chose sodium alginate and bentonite as the blocking components and used an oil-in-water(O/W)strategy to prepare spherical sunscreen particles,which can successfully achieve the blocking of oil-soluble UV filter.