Preperation Of Titanium Dioxide Composite Nonaparticles And Their Application In Sunscreen

In consideration of the traditional small molecule sunscreens which have the problems of large addition and easy to penetrate through the skin into the blood vessels,causing potential health risks,this thesis designs and prepares a series of high molecular broad-spectrum sunscreens.Biomacromolecules with excellent UV absorption,free radical scavenging and adhesion properties were selected and used to prepare a highly effective sunscreen without skin penetration by synergistic UV absorption with titanium dioxide.The sunscreen retains the antioxidant and sun protection functions of biomacromolecules while reducing skin permeability.The main elements are as follows:（1）Titanium dioxide（TiO₂）precursors were prepared by sol-gel method,and（polydopamine-titanium dioxide）（PDA-TiO₂）hybrid nanoparticles were prepared by co-blending TiO₂ with dopamine hydrochloride.PDA nanoparticles with different particle sizes were also prepared to compare the properties of both.The PDA-TiO₂ hybrid nanoparticles were found to have efficient UV protection properties under the synergistic effect of PDA and TiO₂.The basic chemical structure,morphology,UV absorption properties and skin penetration properties of both were investigated.The SPF and cytotoxicity of the sunscreen were also investigated by preparing the nanoparticles as the only sunscreen efficacy ingredients.The results showed that PDA-TiO₂ hybrid nanoparticles had better UV absorption effect than pure PDA nanoparticles,and the higher the PDA content,the more PDA and TiO₂could play a synergistic role.The commonly used benzophenone small molecule sunscreens reach a penetration depth of 18-30μm in the skin and have the risk of penetrating into the blood vessels,while the skin penetration depth of PDA-TiO₂ hybrid nanoparticles is significantly lower at 7-12μm,which is mainly attributed to the adhesion of polydopamine.PDA-TiO₂ hybrid nanoparticles（25 wt%）sunscreen achieved the sun protection factor（SPF）of 33.7±2.9,which can meet the daily sun protection needs,and the cell viability of mouse embryonic fibroblasts were all observed to be over 100%within 48 h.This indicates that the sunscreen is non-cytotoxic,beneficial to cell proliferation and growth,and stable in the long term.（2）PDA@TiO₂ composite nanoparticles were prepared by blending rutile titanium dioxide with dopamine hydrochloride and adding tris（hydroxymethyl）aminomethane to adjust the p H of the reaction.By adjusting the mass ratio of titanium dioxide with dopamine hydrochloride and the p H of the reaction,the thickness of the encapsulated PDA layer（1～7nm）could be regulated.The chemical structure,microscopic morphology,UV absorption properties and skin penetration properties of the particles were investigated.And the PDA@TiO₂ composite nanoparticles were prepared as the only sunscreen efficacy component to explore the SPF and cytotoxicity of the sunscreen.The results showed that the UV absorption performance of PDA@TiO₂ composite nanoparticles was closely related to the thickness of the covered PDA layer under the synergistic effect of PDA and TiO₂.The thinner PDA layer,the better UV absorption effect of the nanoparticles.The skin penetration depth of PDA@TiO₂ composite nanoparticles was within 10μm.When the thickness of the coating layer of PDA increased,the skin penetration depth decreased to a minimum of about 4μm.The SPF of PDA@TiO₂composite nanoparticles（15 wt%）sunscreen reached 162.4±57.6,which was about 8 times of the SPF of TiO₂ sunscreen with the same content.3T3 cells can grow in the PDA@TiO₂ composite nanoparticles sunscreen,and the cell viability reached more than 100%within 48 h with good cytocompatibility and stability.（3）Alkaline lignin（AL）was reacted with dopamine hydrochloride to obtain AL-PDA composite particles,which were then co-blended with titanium dioxide to prepare AL-PDA/TiO₂ composite nanoparticles.The chemical structure,microscopic morphology,UV absorption properties and skin permeation properties of the composite nanoparticles were investigated.AL-PDA/TiO₂ composite nanoparticles were prepared as the only sunscreen efficacy component of the sunscreen,the SPF and cytotoxicity of the sunscreen were investigated.The results showed that the lignin-modified AL-PDA/TiO₂ composite nanoparticles had more significant UV absorption effect than PDA@TiO₂ composite nanoparticles due to the synergistic effect of AL and PDA,and the skin penetration depth was lower,both reaching below 4μm.The SPF of AL-PDA/TiO₂ composite nanoparticles（15wt%）sunscreen reached 241.3±76.7,and the sunscreen was safe and stable with cell viability more than 100% within 48 h.