Study On Anti-Ultraviolet Function Of Bombyx Mori Silk Fibroin Microspheres

Ultraviolet(UV)is the prime factor that damages the skin in our daily life.Overexposure to UV could bring about excessive reactive oxygen species(ROS)in the epidermis,leading to the incrassation of the epidermis,the deposition of melanin and the premature aging of the skin.As a consequence,a great number of sunscreens has been developed to resist UV.However,commercial organic or inorganic sunscreens have been reported to be generating extra reactive oxygen species(ROS)and entering the deep tissues for triggering a serious skin inflammation and other side effects.Thus,there is a great demand for developing new,non-toxic and efficient sunscreens.Recently,sunscreen developing with bio-sourced ingredients are attracting more and more attentions.Silk fibroin(SF),spun from Bombyx mori,is a potential candidate due to its unique functions such as biocompatibility,UV absorbing and ROS-eliminating ability.However,there are still challenges in applying SF as a sunscreen.Regenerated SF is difficult to be preserved in room temperature for a long time,and its UV-inhibition efficiency is also limited.Thus,modification is warrant here for improving the UVprotection efficiency and the stability of SF.Herein,silk fibroin microspheres(SFMP)were applied as a biocompatible and highefficient anti-ultraviolet sunscreen agent.This work investigated the UV resistance,free radical scavenging ability and biosafety performance of SFMP to evaluate SFMP’s feasibility as a sunscreen.The main results of this study are as follows:(1)Preparation of silk fibroin microspheres by self-assembly methodIn this work,ethanol was used to induce the self-assembly of silk fibroin in aqueous solution.The silk fibroin microspheres were further formed and dispersed by ice crystallization at low temperature.Finally,the SFMP suspension was freeze-dried and the silk fibroin microspheres in a diameter of about 1.3 μm were obtained.Absorption spectroscopy showed that the increase of particle size significantly enhanced the UV shielding ability of silk fibroin.Infrared spectroscopy showed the β-sheets of silk fibroin in SFMP increased,slowing down its degradation.Hydroxyl radical clearance showed that the antioxidant property of SFMP was excellent.Therefore,silk fibroin microspheres have the feasibility in anti-UV application.(2)Anti-UV ability of silk fibroin microspheres in vitroThe UV resistance of silk fibroin microspheres in vitro was verified with L929 cells.The results showed that SFMP had excellent biocompatibility and could significantly reduce the UV damage in cells.Specifically,during UV exposure,the protection of SFMP reduced the intracellular γ-H2 AX by 80% and decreased the ROS positive cells by 85.28%,which are significantly better than the results in the titanium dioxide group.(3)Anti-UV ability of silk fibroin microspheres in vivoThe UV resistance of silk fibroin microspheres in vivo was studied with healthy BALB/c nude mice.The adhesion characteristics of silk fibroin microspheres were observed by fluorescence rendering.The results showed that the silk fibroin microspheres did not produce skin penetration,and only exhibited a shedding of 8.98%after adhered to the skin for 8 hours,meeting the requirements of daily application.The nude mouse skin was topically covered with SFMP and commercial sunscreen agent,and the untreated group as the control group,following a high dose of UV radiation on dorsal skin.It was found that the epidermis thickness of unprotected mice was significantly thickened,and the relative thickness reached 217.39% of that of control group,while the relative thickness of silk fibroin microspheres treated mice was only114.33% under the same conditions.The result demonstrated that silk fibroin microspheres can protect skin from UV damage effectively.Moreover,the SFMP treatment reduced inflammatory response,which happened in commercial sunscreen treatment groups.In conclusion,this work verified the new strategy towards the facile construction of nature-inspired sunscreens with high anti-UV efficiency,ROS elimination ability,application stability,and low inflammatory response.