Study On The Preparation And Properties Of EGCG Loaded Niosomes And Its Cryogels

Epigallocatechin gallate（EGCG）,as the main component of tea polyphenols in tea,has anti-aging and whitening effects.However,with multiple phenolic hydroxyl groups in molecular structure,EGCG has the disadvantages of poor stability and low bioavailability,which limit the application of EGCG in cosmetics.With a bilayer structure,niosomes can encapsulate both lipophilic and lipophobic drugs and improve their stability and bioavailability.Meanwhile,compared with liposomes,niosomes have many advantages,such as low cost and good stability.Therefore,in this thesis,firstly,the EGCG loaded niosomes（EN）were prepared by encapsulating EGCG into niosomes,and their stability,transdermal effect and biological activity were characterized.On this basis,polyvinyl alcohol（PVA）and hyaluronic acid（HA）were chosen as gel matrix and PVA/HA/EN cryogels were prepared by freeze-thaw method,only to solve the application limitation of EGCG and broaden its application prospect in cosmetic field.Firstly,EN were prepared by ethanol injection method,the speed and time of high-speed homogenization as well as hydration medium of EN were optimized respectively,with particle sizes,polydispersity index（PDI）,encapsulation efficiency and loading capacity as indexes.The optimal preparation condition was determined as follows.The optimal hydration medium was deionized water and the optimal speed and time of high-speed homogenization were 12000 r/min and 1 min.Under the optimal conditions,the particle size of EN was around 60 nm,PDI was 0.189±0.020,encapsulation efficiency was 79.4%and the loading capacity was 7.97%.In addition,the increase of salt concentration or the decrease of pH in the hydration medium could lead to the increase of the particle size of EN,and EN was unstable under alkaline conditions.According to the storage experiment at room temperature,it was found that the retention rate of EGCG increased from 0 to 61.2%after storage of 60 days under dark conditions.Secondly,Franz diffusion cell was used to investigate the transdermal effect of EN on pig skin.Human skin fibroblasts（HSF）were selected to investigate the cell antioxidant activity（CAA）and anti-UVA damage ability of EN.The transdermal test results showed that compared with EGCG solution（ES）and a mixture of blank niosomes and EGCG（NE）,EN had the best transdermal effect with the highest content of EGCG measured in stratum corneum and skin below stratum corneum.The transdermal mechanism of niosomes was investigated by using total reflection infrared spectrometer.The results showed that EN could improve the hydration of keratin and change the secondary structure of keratin,thus reducing the barrier function of the stratum corneum and promoting the transdermal penetration of drugs.Meanwhile,with the penetration of niosomes,the lipid content of stratum corneum increased and the lipid fluidity declined.The results of CAA experiments showed that,compared with ES,the EC₅₀ value of EGCG decreased from 2.6μg/mL to 1.2μg/mL after EGCG was encapsulated with niosomes,which meaned that cell antioxidant activity was enhanced.UVA-induced cell damage experiments showed that,compared with cells incubated with ES,when the cells were incubated with EN,the cell viability increased from 88.0%to103.4%,indicating that the anti-UVA damage ability of cells was improved.Finally,EN was loaded into PVA/HA composite gels by freeze-thaw method and PVA/HA/EN cryogels were prepared.The results indicated that,with the increase of freeze-thaw cycles,the crosslinking degree of PVA/HA/EN cryogels increased,the structure became denser,the gel strength were improved,and the release speed of the cryogels became slower.When the mass fraction of HA was 0.5%,the storage modulus G’is the largest,reaching 687 Pa,and the structure is the densest.Compared with the control group PVA/HA/ES cryogels,the release rate of PVA/HA/EN cryogels within 24 h reduced from69.04%to 53.96%,the retention rate increased from 83.53%to 98.13%after storage at room temperature for 2 months,and the total transdermal amount increased from 0.22μg/cm² to0.49μg/cm².