Stable liposomes containing carboxymethyl chitosan (CMC) were prepared and characterized. CMC was introduced in the phosphatidyl choline (PC) liposomes by different methods; firstly, CMC in a free state in the aqueous phase; secondly as a coat (coupled); and finally as a conjugate of dapsone. The stability of liposomes was assessed by their disintegration in ethanol and surfactants. Both hydrophilic bromothymol blue and lipophilic dapsone were encapsulated in these liposomes and their in vitro release studies were carried out at 37 degrees C using different media, namely, phosphate buffer (pH 7.4), 0.02 N-HCl and 1% mouse plasma. The conjugate of dapsone with CMC present in PC liposomes gave the best results in its stability as compared to other modified liposomes. The release data of dapsone also confirmed the results of the stability studies on liposomes. CMC-dapsone conjugate released the dapsone much slower in all three media than did PCCMC and PCCMC-coat liposomes.
Disintegration by surfactants on egg-yolk phosphatidyl choline (PC) vesicles, stabilized with polycholesteryl methacrylate and carboxy methyl chitosan, was investigated by measuring the amount of marker dye (bromothymol blue) released from the vesicles. In all the studies at pH 7.4 anionic and nonionic surfactants caused vesicle disintegration at low concentrations while cationic surfactants produced breakdown of vesicles at high concentrations. It was found that the modified liposomes disintegrated in the following order: Polymeric liposomes less than carboxymethyl chitosan coated/stearic acid/oleic acid containing PC liposomes less than cholesteryl methacrylate monomer containing PC liposomes/PC liposomes Polymeric liposomes were found to be the most stable compared with all other types. This may be explained due to the filling of the pores in the lipid structure which in turn block the surfactant penetration into phospholipid bilayers. In contrast to unsaturated fatty acid (oleic acid) saturated fatty acid (stearic acid) containing liposomes are more stable.
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