Effect Of Membranes With Different Phospholipids On The Stability Of Liposomes

Liposomes are superfine spherical particles of bilayer, which are formed by dispersed phospholipid in water. It has been concerned as drug carriers for a long time because of its good biological activity. However, liposomes are susceptible to light, heat, oxygen, metal ions and other factors, these poor stability have limited the widespread use of liposomes greatly, thus, how to increase the stability of the liposomes become a hot research field. In this study, phosphatidylcholine(PC), dipalmitoyl phosphatidylcholine(DPPC) and palmitic acid-modified PC are used as the membrane material for the preparation of liposomes. Taking average particle size, particle size distribution, Zeta- potential, encapsulation efficiency(EE) as the stability factors of the liposomes, and provide a theoretical basis for improving the stability of the liposomes.Take Novozym435 enzyme catalyze powder phospholipids and explore the best reaction conditions of phospholipids and palmitic acid,the optimal conditions are : substrate concentration(phospholipid/n-hexane, g/mL) 20%,enzyme dosage(enzyme/phospholipids, g/g) 20%, reaction temperature 50℃, the reaction time 50 h, under these conditions, the catalyzed reaction prepare high palmitic acid content of PC, the content of palmitic acid of PC was increased from 14.37% to 33.8%.Prepared Vitamin E(VE) liposomes and laetrile liposomes through thin-film method, dispersion method, ethanol injection method, reverse evaporation method, fusion method respectively. Compare the advantages and disadvantages of various preparation methods of different drug liposome by taking size, Zeta-potential, EE as the stability factors of the liposome: the EE of VE(fat- soluble)liposome by the ethanol injection method is highest,was 28.32%, PDI was 0.294, particle size was105.22nm; the EE of laetrile(water-soluble)liposome by reverse evaporation method was highest,was15.28%, PDI was 0.201, the particle size was 182.7 nm。Using ethanol injection method to prepare VE liposome, The optimal preparation conditions were obtained by single factor experiment and orthogonal array testing, as follows: the ratio of phospholipid to cholesterol was3:1(g/g),phosphate buffer pH=7.4, Tuwen80 dosage27.3%(based on the total mass of raw material).Under these conditions, the EE of VE was 29.78%,Zeta-potential was-5.5mv。The Zate-potential and stability of liposomes were improved by using glycol fatty acid succinic acid monoester,the Zete-potential of liposomes increased almost twice more than before and the EE increased to 43.6%.Using reverse evaporation method to prepare laetrile liposomes, taking EE as index, Optimize the preparation method by single factor and orthogonal experiments, the best preparation conditions as follow: the ratio of PC and cholesterol 3:1, oil-water ratio 3:1, PBS pH = 7.0, ultrasonic emulsification time 4 min, under those conditions, the EE of laetrile liposome was 23.34%. At 4 ℃, 25 ℃, The EE fell by 64% and 81.8% within two weeks, respectively. At 40℃, the EE of liposome was fell 53.1% in three hours, the test results show that high tempreature accelerates the oxidation of liposome membrane easily, hence the stability of liposomes reduced.PC, DPPC, modified PC and modified PC including free fatty acid were used to prepare liposomes respectively for investigating the effect of phospholipids saturation on the stability of liposomes. Measured the change of the size, PDI, Zete-potential, EE, lipid peroxide, the EE dropped 64.12%、43.88%,51.09%,76.45%, respectively,within two weeks; the maximum change of the absorbancy of lipid peroxide at A500 nm were:0.223,0.164,0.104,0.301, respectively. Liposome patterns were observed by TEM, and it was found that the liposomes prepared by modified PC containing free fatty acids have the biggest morphological change, the liposomes prepared by DPPC or modified PC had legible border and regular patten yet. Study the release of Liposomes in simulation artificial gastric juice, the concentration of the drug increased 11.74%, 0.81%, 9.4% and 11.74% in two hours, respectively, the results show that the liposomes which build on DPPC have the best stability in gastric juice.