Study On Preparation And Property Evaluation Of Chitosan/Carboxymethyl Chitosan Coated Vitamin E Liposomes

Liposomes are microvesicles, the structure of liposomes is similar to biofilm double-layer structure since liposomes are made of phospholipids which are the same material as the cell membrane. Phospholipids molecules have a head group and a tail group. The head is hydrophilic, the tail, which is made of a long hydrocarbon chain, is hydrophobic. In the presence of water, the heads are attracted to water and line up to form a surface facing the water. The tails are repelled by water, and line up to form a surface away from the water, and thus liposomes formed.Chitosan is prepared by deacetylation of chitin, and it's positively charged and soluble in acidic aqueous solution. Carboxymethyl chitosan is one of the most important derivatives of chitosan, the advantage of carboxymethyl chitosan compared to chitosan is carboxymethyl chitosan can be dissolved in neutral aqueous solution while chitosan can only be dissolved in acidic aqueous solution.Liposomes, Chitosan and Carboxymethyl chitosan, all of them can be used as drug delivery system. Liposomes are normally more biocompatible than the chitosan and carboxymethyl chitosan since phospholipids which are used to prepare liposomes are the same material as the cell membrane, besides liposomes have non-immunogenicity. The disadvantage of liposomes is instable, while chitosan and carboxymethyl chitosan are normally rather stable compared to phospholipids which are used to make liposomes; In order to combine their advantages and avoid the disadvantages, the liposmes are coated by chitosan and carboxymethyl chitosan respectively. The chitosan and carboxymethyl chitosan coating can improve the stability of liposomes.Preparing negatively charged vitamin E liposomes, and then the vitamin E liposomes are incubated with chitosan which is a kind of macromolecule with polycation to make chitosan coated vitamin E liposomes; Preparing positively charged vitamin E liposomes, and then the vitamin E liposomes are incubated with carboxymethyl chitosan which is negatively charged in aqueous solution to make carboxymethyl chitosan coated vitamin E liposomes. Transmission electron microscope pictures and Zeta potential analyses showed both chitosan and carboxymethyl chitosan were successfully coated on the two kinds of liposomes respectively.In the preparing period of vitamin E liposomes, 5 methods for preparing vitamin E liposomes are used and compared. The results showed the film hydration method has the highest coating efficiency (82.5%) and higher retention rate (91.4%), and the optimal proportion of preparing vitamin E liposome is confirmed (phospholipids : vitamin E : cholesterol= 20:1:1.87). Transmission electron microscope pictures show the vitamin E liposomes are spherical or approximatively spherical and have typical fingerprint characteristics. The vitamin E liposome particles are well distributed and the mean particle size is 35.2nm.Coating efficiency, yield and drug loading rate of vitamin E of chitosan/carboxymethyl coated liposomes and uncoated liposomes were determined. To compare the coated and uncoated liposomes, the results show that both chitosan and carboxymethyl lead to the decrease of the coating efficiency, yield and drug loading rate, and for each MW of chitosan/carboxymethyl chitosan, the coating efficiency, yield and drug loading rate of vitamin E are similar, i.e. MWs have no effect on them. The concentrations of chitosan/carboxymethyl chitosan affect the coating efficiency, yield and drug loading rate remarkably, with the concentrations increase, the coating efficiency, yield and drug loading rate decrease, for the minimum concentrations(0.1%) of chitosan/carboxymethyl chitosan, the coating efficiency decrease 9.3%/4.3% after coating. Conserving rate and sedimentation volume rate of chitosan/carboxymethyl coated liposomes and uncoated liposomes are also determined and compared. The results show both chitosan and carboxymethyl lead to conserving rate increase and sedimentation volume rate decrease, for each MW of chitosan/carboxymethyl chitosan, the conserving rate increase and sedimentation volume rate are similar, i.e. MWs have no effect on both of them, but the concentrations of Chitosan/Carboxymethyl chitosan affect the conserving rate and sedimentation rate obviously, with the concentrations increase the conserving rate increase but sedimentation volume rate decrease. Storing at 4℃under the condation of avoiding light for 7 days, the vitamin E conserving rate of 0.8% chitosan-coated liposomes is 37.0% higher than the uncoated liposomes, and the sedimentation volume rate is 6.6% lower. Storing at 37℃under the condation of avoiding light, the vitamin E preserving rate declines fast, in the 7th day, the vitamin E conserving rates of both the two kinds of vitamin E liposomes decline to 0%, while vitamin E conserving rate of the 0.8% chitosan coated liposomes is 9.9%, and for the 0.8% carboxymethyl chitosan coated liposomes is 13.5%. Comprehensively considering, the stability of vitamin E liposomes is improved effectively after the Chitosan/Carboxymethyl chitosan coating, although coating efficiency, yield and drug loading rate of vitamin E decrease slightly, i.e. Chitosan/Carboxymethyl chitosan coating improves the applicability of liposomes.