The Study Of Stability And Nano-mechanical Characteristics Of Liposome Modified By PVP

Liposomes have been widely used as a carrier in drug targeting and long-time cycling transportation, as well as in experiments of molecular biology. The stability is very important to liposome. Nowadays, how to improve the stability and how long it kept in vivo is a significant issue. The stability of liposome are related to its nano-structure and biophysics attributes, and has become a hotspot of study for years.In this paper, we prepared normal and PVP (Poly vinylpyrrolidone) modified liposomes are prepared by film scattered method. Then we measured the EE (entrapment efficiency) of two types liposomes were measured by ultra-high speed centrifugation separation liposomes and free drugs. The results showed that, the EE of liposome which is prepared when phospholipids:cholesterol=6:1(m/m) is the highest. But its stability is poor, and the EE will reduce quickly. The EE and stability of liposome modified by PVP were measured through the same method. It turned out; the EE of liposome modified by PVP is lower than normal liposome prepared with same materials. But the liposome stability has been obviously improved. It proves that stability of liposome can be improved when it modified with PVP.Liposomes were studied by AFM (atomic force microscope) imaging observation. The results show that, the stereo structure of normal liposome is poor on mica. Liposomes appear to have concave phenomenon, and gather together and fusion. At same time liposome modified with PVP appears to be great stereo structure on mica. And they are hemispheres. The dispersive of liposomes great. This part shows that, nano-structure of liposome modified with PVP has been changed by PVP, and it will improved its stability. The structure attribute of liposome on mica can be characterized by "rigid". The calculate method of rigidity has been found by Koji Nakano et. Rigidity is the ratio of particles’diameter measured by DLS (Dynamic Light Scattering) and the height of liposome on mice measured by AFM. The results show that, the rigidity of normal liposome on mice is0.3893while liposome modified with PVP is0.5085. This result agrees with atomic force microscope imaging. The enhancements of the rigidity of liposome can improve the stability of liposome in vivo.Force curve of AFM can be used to analyze nano-mechanical properties of liposome. The effect of PVP modification to liposome was analyzed by force curve. The results show that, the elastic force of normal liposome is lower than liposome modified by PVP. The height of liposome on mice decreased after it had been modified by PVP. And abundant surface charge of liposome interfered the retract of the probe. The study revealed that, nano-structure of liposome has changed and the elastic force will be improved when it has been modified by PVP. It will contribute to keep its well stereo structure. The most importantly, the surface charge of liposome can be reduced obviously after modifying. And it will weaken the gathering and fusion of liposomes effectively; thereby/accordingly the stability of liposome will be improved...