| dc.description.abstract | The behavior aggregation and fusion of loposome, both the structure of lipid bilayer and the interactions between liposomes play a very important role. In this research, the stability of lipid bilayer structure is discussed by using the shear stress coupled with the lipid released from the liposomal bilayer. At the same time, the dilution heat of liposomal suspension can be measured by isothermal titration calorimetry (ITC). In addition, the second virial coefficient b2 in the system of liposomeal suspension are also determined by using a mathematical model plus the measurement data from dilution heat, moreover, the behavior of interactions between liposomes can be explained from the standpoint of the second virial coefficient. Furthermore, the energy barrier parameter (b2/B0) relating to the aggregation and fusion behavior of liposomes can be interpreted in conjunction with Square-Well energy equation.
Our experimental data indicates that the net interaction force between PC liposomes are repulsive. Also, the effective range of repulsive force between PC liposomes can reach as faraway as 80 times of their diameter (around 8 x 10-4cm). So far as the incorporation of cholesterol into the PC bilayer, our experimental results also indicates that the absolute zeta potential becomes more negative, this data indicate that the repulsive electrostatic force between liposomes have become larger. In addition, the values of b2 and b2/B0 have become larger as well. Another way of explaining this data that incorporating cholesteril into the PC bilayer promotes the net repulsive force (2.5 times of its effective repulsive force) between PC liposomes, in addition to the increment of energy barrier in respect of the behavior of aggregation and fusion. Moreover, incorporating cholesterol into the PC bilayer make the liposome more rigid and sustains more severs shear stress in our shear forces studies; in other words, incorporating cholesterol into the PC bilayer can promote the stability of PC bilayer structure. More importantly, incorporating cholesterol into the bilayer can reduce the amount of free lipid, pointing out that this incorporation can increase the interactive force of lipid molecules and enhancing the stability of PC bilayer. Finally, our experimental results also indicated that the incorporation of cholesterol into the bilayer would reduce the liposomal size changes. In other words, incorporation of cholesterol can inhibite the behavior of aggregation and fusion and enhance the physical stability of liposome.
This work also reveals that temperature and PC liposomal stability are correlated with each other. The stability of PC liposomes are likely to decline with a rise in the temperature, and the elevated temperature effect is evidence of the rigidity or curvature of the PC liposome. Furthermore, the repulsive interaction potential (or energy barrier) between the PC liposome declines with a rise in temperature
The second part of this research is to examines how PEG2000-grafted lipid affect the surface properties of the PC liposomal bilayer membrane by the zeta potential and interaction potential measurement by microcalorimetry. In this studies Liposome were prepared from mixtures of egg- phosphatidylcholine (PC), cholesterol and distearoyl-phosphatidylethanolamine covalently attached poly (ethylene glycol) of molecular weight 2000 (DSPE-PEG2000).
Experimental results demonstrated that the absolute value of the zeta potential of PEG2000-grafted liposome decreased from | en_US |