Tan, Hsiao Wei (2014) Rheological evaluation of chitonated fatty acid liposome in carbohydrate-based gel / Tan Hsiao Wei. PhD thesis, University of Malaya.
Abstract
Liposome in gel preparation has opened up a new dimension in pharmaceutical formulation especially topical application as gels usually have longer contact time with the skin. In this study, the liposomal gel was prepared by mixing surface modified oleic acid (OA) liposomes into a carbohydrate based gel. The surface of oleic acid liposomes was modified using different molecular weight of chitosan (Ch1 and Ch2) and Npalmitoyl chitosan with different degree of acylation (Ch2P1 and Ch2P2) thereby providing a cloak structure on the surface of the liposomes. The surface modification of the OA liposomes by the Chs (Ch1 and Ch2) and Ch2Ps (Ch2P1 and Ch2P2) was characterized using microscope images and physicochemical properties such as zeta potential and the size of the liposomes. The micrographs obtained from the transmission electron microscope (TEM) showed that the Chs-modified and Ch2Ps-modified OA liposomes were spherical in shape and appeared to be dark in colour. It was mainly due to the present of the Chs and Ch2Ps on the lipid surface of the OA liposome that thickened the lipid layer and increased its opacity. The surface modification has also enhanced the OA liposome rigidity. After surface modification, the size of the Chs- and Ch2Ps-modified OA liposomes was decreased by at least 20 nm as compared to the unmodified OA liposomes. The decrease in the liposome size was also accompanied with the increase of their zeta potential. The increase of the zeta potential of the surface modified OA liposome from -86 mV to -60 mV indicated that the Chs and Ch2Ps had successfully modified the surface of OA liposomes. The carbohydrate based gel was prepared from the mixture of iota carrageenan (ιC) and carboxymethyl cellulose (CMC). The presence of CMC in ιC gel showed the improvement of the flexibility and cohesive energy of the gel. The gel mixture with 5:5 iii ιC to CMC ratio has been found to be the optimum composition. Under this optimum composition, the gel matrix showed optimum flexibility and elasticity. The liposomal gels were prepared by dispersing the liposomes into the optimized gel matrix. Based on the rheological results, the presence of liposomes enhanced the elasticity and viscosity of the liposomal gel. The liposomal gels showed greater shear thinning effect indicating a better spreading ability of the liposomal gels as compared to the pure 5:5 ιC-CMC mixed gel. However, the changes in the viscous modulus (G”) and the n value obtained from creep test that described the physical entanglements within the liposomal gel were negligible. These results indicated that the liposomes do not alter the internal gel network structure, but accommodated in the void spaces in the gel. At the same time, the gel matrix could act as a protective layer for the liposomes towards disruption effect from the environment.
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