| Vitamin C also known as ascorbic acid,is necessary for the human body and can only be obtained exogenously as a micronutrient.Studies have shown that its antioxidant ability is very significant,and can protect the human body from free radicals damage caused by oxidative pressure,topical application of vitamin C can achieve whitening of skin,vitamin C is also important in treating skin pathologies ranging from the mild skin inflammation to skin cancer.But the practical application in the field of cosmetics has been greatly limited due to it is extremely sensitive to oxygen,alkali,high temperature and other external factors.Therefore,the preparation of hydrogels containing solid lipid microparticles(SLM)dispersion loaded vitamin C was to improve the restriction of vitamin C applied in the cosmetics.a-lipoic acid is a coenzyme exist in mitochondria of the cell involved in a number of redox metabolism process,it is also the essential nutrients in the human body,and can remove the free radicals that accelerated the aging and pathogenic process of human cells,a-lipoic acid is known as the "universal antioxidant" widely used in the treatment and prevention of heart disease,diabetes and other diseases,and can regenerate other antioxidants.But it is also limited in the application of topical skin because of its poor water solubility,sensitive to light and heat,so the preparation of hydrogel containing a-lipoic acid loaded nano-structured lipid carrier is also necessary.In this paper,vitamin C SLM was prepared by a modified two-step method.Orthogonal experiment was designed to determine the factors influencing the preparation of primary emulsion of SLM,and then select the hydrophilic emulsifier to finally determine the composition of SLM,ALA as the protective agent to further avoid the oxidation of vitamin C.It showed that the system has better chemical and physical stability,and the structure of the w/o/w multiple emulsion can be observed by the optical microscope after SLM self-emulsify in water.Then,a natural xanthan hydrogel matrix and a synthetic carbomer gel matrix were prepared respectively,and then the aqueous dispersion of the vitamin C SLM was mixed with the gel matrix to prepare the vitamin C SLM hydrogels.The physical stability and simulated skin retention rate of SLM loaded xanthan gum hydrogel were better than those of carbomer hydrogel system.In the study of chemical stability,the content of vitamin C in gel was almost not reduced within 5 weeks,which indicated that the system had a good protective effect on vitamin C.Moreover,in the in vitro release experiment,the vitamin C SLM xanthan gum hydrogel showed a better sustained-release effect.Secondly,based on the SLM of vitamin C in the previous chapter,two kinds of composite hydrogel matrix were selected,including xanthan gum and carbomer composite gel,xanthan gum and locust bean gum compound gel.The storage stability and spreadability of two kinds of composite hydrogels were compared and the optimal xanthan and carbomer composite hydrogel were subsequently characterized.The results showed that vitamin C has a good stability in the complex gel.In the viscosity test,the gel exhibits a phenomenon of remarkable shear thinning,which makes it easy to spread on the skin.Both in vitro release and transdermal tests showed good experimental results.DPPH free radical experiments indicated that the gel system of vitamin C can still play a role in scavenging free radicals.Tyrosinase inhibition experiments showed that vitamin C still can play a role in inhibit the production of melanin to whiten skin after encapsulated.In vitro the cytotoxicity experiments of skin fibroblast L929 showed that low concentrations of vitamin C SLM composite hydrogel is almost non-toxic to the human cells.At the same time,it has a good biocompatibility because the pH value of the gel is close to neutral.Finally,a-lipoic acid loaded nanostructured lipid carriers(NLC)were prepared through high-pressure homogenization method after screening of lipid and emulsifier.The particle size of obtained system was 88.5 ± 0.75 nm,the PDI was 0.172 ± 0.06,the zeta potential was-10.80 ± 1.32 mV and the encapsulation efficiency was 94.87 ± 0.43%.The stability of the system is good,and a regular spherical structure was observed under transmission electron microscope(TEM).The particle size increased to 96.75 ± 0.83 nm with a PDI to 0.198 ± 0.05 and zeta potential to-20.30 ± 0.93 mV.In the viscosity test,the gel also exhibits a shear thinning phenomenon.In vitro release experiment showed that the sustain-release phenomenon of lipoic acid loaded NLC hydrogel was very obvious.In addition,the pH value and moisturizing properties is also accorded with the requirements of cosmetic formulations.All in all,the two kinds of micro/nano carrier-loaded hydrogels have shown a great potential in cosmetics. |
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