The Effect Of Pluronic Modification On The Structural Characteristics,Stability And Cytotoxicity Of Liposomes

Liposomes are widely studied in biomedicine and food science as delivery systems.However,the application of liposomes were limitied due to their physicochemical instability and lack of active targeting specificity.The modification of liposomes,neither on surface or in membrane,offers solution to solve the above issues.Pluronic is a non-ionic surfactant,composed of hydrophilic poly(ethylene oxide)(PEO)blocks and hydrophobic poly(propylene oxide)(PPO)blocks.They are arranged in triblock structure: PEO–PPO–PEO.Previous studies have shown that Pluronic can effectively bind on the surface of liposome and improve its stability.However,the effect of Pluronic modification on the structural characteristics of liposomes,mechanical behavior and the interaction mechanism has not been fully understood.This project mainly focused on the following subjects:(1)Three Pluronic with different PEO and PPO blocks were used to modify liposomes.The influence of Pluronic modification on the physicochemical properties and structural characteristics of liposomes were studied.Curcumin was then selected as a model drug to study the effect of Pluronic modification on the physical stability and digestive properties of curcumin in liposome.(2)Pluronic F127 was used as modifier,the effect of Pluronic F127 concentration on the physicochemical properties,structural properties and carrier properties of liposome were discussed.Moreover,the effect of dynamic high pressure microfluidization(DHPM)treatment on the interaction between Pluronic F127 and liposome was also discussed.(3)Folic acid targeted Pluronic F127 curcumin liposomes were prepared to study its targeting behavior of in human oral epidermal cancer cells(KB cells).The results were displayed as following:1.Three different Pluronic(F127,F87 and P85)were choosen as modifiers.These Pluronic modified liposomes were prepared by traditional thin film evaporation combined with DHPM technology.The control liposomes(without any modification)were also prepared by the same method.The DLS results showed that the particle size of liposomes decreased after the modified with Pluronic F127,F87 and P85.The TEM observation comfirmed that the modified liposomes were all spherical in shape,and membrane fluidy study showed that the membrane stability of these liposomes increased in the following order: Lps < F87-Lps < F127-Lps < P85-Lps.Cytotoxicity test showed that F127-Lps and F87-Lps possessed good biocompatibility.Curcumin was choosed as a model drug to study the effect of Pluronic modification on the carrying capacity of liposome.The results showed that the encapsulation efficiency of curcumin were about 89%,Non-Fickian transport was the main release mechanism for cur-Lps,cur-F127-Lps and cur-F87-Lps,and first-order model was the main release mechanism for cur-P85-Lps.In addition,Pluronic modification can enhance the pH stability and thermal stability of curcumin.The in vitro simulated gastrointestinal tract studies suggested that Pluronic modification could significantly improve the absorption of cur-Lps.Bioaccessibility of curcumin liposomes increased in the following order: cur-Lps < cur-F87-Lps < cur-P85-Lps < cur-F127-Lps.2.Pluronic F127 was selected as a modifier,liposomes with different mass ratios of phospholipid and F127(1:0,1:0.25,1:0.5,1:1,1:2)were prepared by thin film evaporation combined with DHPM technology.The results of TEM indicated that Pluronic F127 at low concentration may incorporate into liposomes and form spherical and lamellar structure,while Pluronic F127 at high concentration can form mixed aggregates with spherical micelles and lamellar vesicles.With the increasing of Pluronic F127 concentration,the membrane stability of liposomes was enhanced.Curcumin was encapsulated into F127-Lps(cur-F127-Lps)with an entrapment efficiency of 89%.The higher the ratio of Pluronic F127 was,the slower the release rate of curcumin.Non-fick diffusion is the main release mechanism of cur-Lps and curF127-Lps(1:0.25),and the first-order kinetic model is the release mechanism of curF127-Lps(1:2).In addition,DHPM treatment could obviously reduce liposomal particle size.At the same time,the microstructure of liposomes was transferred from irregular multilamellar to unilamellar membrane structures,and the functional groups of liposomes change slightly.The subtle difference of structure might be attributed to the incorporation of PPO chains.Furthermore,the storage and membrane stability of liposomes can be improved by DHPM treatment.3.FA-F127 was synthesized by solution polymerization.The NMR and FTIR results indicated that FA-F127 was successfully synthesized.The cur-FA-F127-Lps was prepared by thin film evaporation combined with DHPM,and the cur-F127-Lps without folic acid was also prepared as a control.The in vitro release study indicated that the release of curcumin from cur-FA-F127-Lps presented initial burst release and then slow release,which was similar to the release behavior of cur-F127-Lps.Which means the modification of folic acid on F127 could not change the in vitro release behavior of cur-F127-Lps.MTT experiments indicated that the blank liposomes F127-Lps and FA-F127-Lps without curcumin had no cell cytotoxicity,indicating that the blank liposomes had good biocompatibility.However,after loading curcumin,the cytotoxicity of cur-FA-F127-Lps containing folate was stronger than that of nontargeted cur-F127-Lps,demonstrating that folic acid could effectively transport curcumin liposomes to KB cells which overexpressed folate receptor.Moreover,the longer the action time,the more obvious the targeted effect.