Effect On Stability Of The Amphiphilic Diblock Copolymers Pluronic Interact With PC Liposome

Liposomes have the qualities of low toxicity, breakable in the bodies and good biocompatibility. As the drug carriers, they can increase the targeting effect and bioavailability of the drug, and improve effect and decrease toxicity. Liposomes are prepared from mixtures of PC, cholesterol and Pluronic by film-supersonic method and freeze-drying. Isothermal titration calorimetry, Dynamic light scattering, Differential scanning calorimetry and Contact angle method are employed to measure the stability of liposomes.1. Isothermal titration calorimetry and Thermodynamics model are combined to deduce the values of the second virial coefficient b2 which can describe the interaction between any two liposomes. The results indicated that the values of Pluronic-grafted PC liposomes are all positive and larger than pure PC liposomes, which shows that Pluronic can improve the stability of liposomes. Of all kinds of Pluronic, F108 (PEO)132(PPO)50(PEO)132 has the largest value.2. The size of liposomes at different days are detected by Dynamic light scattering. Pluronic-grafted PC liposomes show the lower increase rate of size than pure PC liposomes. The study shows that Pluronic can effectively inhibit the fusion of liposomes. F108(PEO)132(PPO)50(PEO)132 shows the best effect which accords with the results of Isothermal titration calorimetry.3. Differential scanning calorimetry is applied to measure the transition temper-ature of liposomes. The transition temperatures of Pluronic-grafted PC liposomes are higher than than pure PC liposomes. F88(PEO)103(PPO)39(PEO)103 with two tran-sition temperatures indicates that there are two patterns in the interaction between F88 and PC liposomes. F127-modified liposomes have single phase and the higher transition temperature. So we conclude that F127(PEO)100(PPO)65(PEO) 100 with the longest PPO chains is a good stabilizer.4. The contact angle of F88 and PC mixed film are measured by redistilled water and diiodomethane. The contact angles of diiodomethane correlate with the NPEO:NPPO ratio and concentration of Pluronic. While the NpPE: NPPO ratio or concentration increases, the contact angle of diiodomethane decreases. Comparing with other Pluronic, F108 has the smallest contact angle of diiodomethane.