Unusual in vitro degradation behavior of physically cross-linked liposome gel network

In this study, the in vitro degradation behavior of self-assembled liposome gel was investigated, especially in comparison with rheological studies. The liposome gel, physically cross-linked by hydrophobic interactions, was obtained by mixing liposome solution with cholesterol-end capped polyethylene glycol. The liposome gel was found to have rheological behavior similar to that of Maxwell model. The plateau modulus of the liposome gel, an important value to reflect the effective cross-linking density among the network, was dependent on both the liposome concentration and the polymer concentration. When the liposome gels were exposed to an aqueous solution, they first showed a period of swelling phase due to adsorption of water and then a dissolution phase began, leading to the full degradation of the network. The liposome gel with higher plateau modulus (i.e. higher effective cross-linking density) was found to degrade more slowly, indicating that the degradation behavior of the gel was closely related with the rheological properties. In order to study the gel degradation mechanism more directly, dextran blue-loaded liposome gel was prepared. In the initial period of the liposome gel exposure to the aqueous solution, the dextran blue release was of Fickian diffusion transport behavior. After that period, the release mechanism was found to be of Super Case II transport, which was gel matrix relaxation controlled.