Size Separation And Characterization Of Chitosan Decorated Liposomes

Liposomes having colloidal structures formed by self-assembly phospholipids have been used as drug carriers for the treatment of various diseases due to its excellent biocompatibility. However, the liposome stability and specificity of targeting need to be improved to achieve higher performance with minimum side effects. Although passive targeting of stealth liposomes to tumor tissue can be achieved by enhanced permeability and retention effect, modified liposomes that can actively target a certain organ or tissue, a particular cell, or even an intracellular compartment, are highly attractive but still elusive. Chitosan is a biodegradable and biocompatible cationic polysaccharide which can bind to and stabilize liposomes. In this thesis, the band broadening of gel permeation chromatography(GPC) was studied by coupling with a multi-angle laser light scattering(MALLS) detector. The molecular weight distribution of chitosan was determined by GPC-MALLS. Chitosan samples of different molecular weight were employed to decorate liposomes, and the size distribution of the resulting chitosan-decorated liposomes(chitosomes) was studied. The main results are as following:1. The band broadening of aqueous GPC columns was studied by coupling with a multi-angle laser light scattering detector, using narrow polyethylene glycol(PEG) and polyethylene oxide(PEO) samples. The determined spreading factor of PEG/PEO increased with increasing molecular weight between 4.0×103 and 1.3×106. True molecular weight distributions of these samples were obtained with band broadening correction. Despite the presence of band broadening in the columns, the monodisperse scaling law between radius of gyration and molecular weight of PEO is established to be Rgz(nm) = 0.0272 Mw0.56, indicating that the long PEO chains take a swollen random coil conformation in water due to the presence of excluded volume effect.2. The colloid titration, element analysis and 1H NMR methods were employed to measure the degree of deacetylation(DD) of chitosan samples. The molecular weights of these chitosan samples were determined by GPC-MALLS. The established scaling law between molecular size and molecular weight indicated a random coil conformation for chitosan in the HAc-Na Ac buffer. We also performed asymmetrical flow field flow fractionation with multi-angle light scattering(AF4-MALLS) studies on these chitosan samples to establish a new method for the separation and characterization of chitosan.3. Chitosan samples of different molecular weight were employed to decorate DOPC liposomes. The size distributions of the resulting chitosomes were studied by dynamic laser light scattering and AF4-MALLS. It was found that the size of the chitosomes increases with increasing molar ratio between chitosan and DOPC lipids. Such an increase is more significant for chitosan with higher molecular weight. The results from AF4-MALLS indicated that chitosan was successfully decorated on the surface of liposomes, but there are still some free chitosan unattached to the liposomes in the solution.