| Liposomes have long been thought as potential drug delivery systems. One of the major problems with liposomes was their quick uptake by the phagocytic cells of the circulatory system. The advent of sterically stabilized or "stealth" liposomes, with their long circulating property, has opened the door for increased use of liposomes as targeted delivery vehicles in vivo. Poly(ethylene glycol) (PEG) is the main stealthing molecule used these days. Stealth liposomes, in different form and mechanism, are being used for a variety of purposes like drug and gene delivery, immunotherapy etc.; Another problem in using liposomes in vivo is the indiscriminate release of encapsulated materials resulting in ineffective delivery. Also the liposomes, being stealth, would not readily adhere to the site of interest and one way around that is to make them de-stealth at the site by some external manipulation. Several groups have attempted to locally release encapsulated material by external triggering such as temperature, pH or light. The advantage of such system is controlled release at the site of interest making the drugs more available there.; In this thesis, we have studied different polymer molecules that can cause temperature-sensitive steric protection to liposome surfaces as well as planar lipid bilayers. Additionally, these polymers can be used to unprotect a surface and trigger release of liposomal internal content by subjecting them to temperature change. We have used Pluronic molecules, which are tri-block copolymers of PEG and poly(propylene glycol) (PPG), as substitute of PEG lipid in order to form sterically protected surfaces against cell adhesion that can be made unprotected by thermal treatment in vitro. We have also studied the physical nature of interaction between Pluronic molecules and the liposomal bilayer during thermal treatment.; The important contributions of this work are temperature-sensitive steric protection and de-protection of conventional liposomes using Pluronic F127 molecule and precise temperature-controlled release of the encapsulated cargo of different molecular weights from these liposomes. |
