Polymer-coated liposomes structure

In designing polymer-coated liposomes containing peptide drugs, attention should also be paid to their structure. Drugs can be loaded into a liposomal... 

Partial to complete 3-0-octadecylated polysaccharides exhibited characteristic solution and solid properties based on hydrophilic-hydrophobic structures. These polymers are suggested to form micellar conformations in water and in chloroform polysaccharide-coated liposomes, polymeric membranes, and thermotropic liquid-crystalline mesophase, depending on the octadecyl content. Hydrolysis of 3-deoxygenat-ed, 3-0-methylated, and 3-0-octadecylated dextrans by an endo-acting dextrans is compared. The possibility of a combshaped branched polysaccharide toward cell-specific biomedical materials is discussed. 

The surfaces of liposomes have been coated [17] with thermosensitive pol5uners such as poly(A -isopropylacrylamide) [poly(NIPAM)] by taking advantage of the phase transition of polymers. The molecular structure of a hydrophobically modified poly(NIPAM), which has been studied in the preparation of temperature-sensitive Uposomes [17], is depicted in Fig. 7. Poly(NlPAM) exhibits a low critical solution temperature (LCST) around 32°C, and the LCST can be altered toward the body temperature by co-pol5unerization [56], The pol5uner is in an expanded form at low temperature, but above the critical temperature it is in a contracted form. The interactions of SUVs and hydrophobically modified poly(NIPAM) were studied by fluorescence spectroscopy [88]. More recently, sonicated DPPC and egg PC Uposomes coated with a copolymer of NIPAM and octadecylacrylate in a molar ratio of 100 1 were prepared [17,89], It was shown that above the LCST of the copolymer, the release of calcein and carboxyfluorescein from... 

First, the partition of hydrophobized polysaccharide (HP)-coated liposomes was investigated in aqueous two-phase systems such as polyfethylene oxide) (PEO) (top phase)/pullulan (bottom phase) and poly(ethylene oxide) (top)/ dextran (bottom phase). HPs such as cholesterol-bearing pullulan, dextran, and mannan nicely coated the liposomal surface. When conventional uncoated liposomes were added to the aqueous two-phase system, they mostly located at the interface between the two polymer phases. The HP-coated liposomes, on the other hand, were significantly partitioned into the bottom polysaccharide phase, depending on the structure of the HP on the liposomal surface. 

The effects of coating the liposomes with HPs on the partition in two different aqueous two-phase systems are summarized in Tables 1 and 2 and Fig. 2. The conventional liposomes without any HP coat locate mostly at the interface between the two polymer phases as reported previously [5-7]. On the other hand, the HP-coated liposomes were significantly partitioned to the bottom polysaccharide-rich phase. The extent of the partition depended on the chemical structure and density of HP on the liposomal smface. 

Principles to stabilize lipid bilayers by polymerization have been outlined schematically in Fig. 4a-d. Mother Nature — unfamiliar with the radically initiated polymerization of unsaturated compounds — uses other methods to-stabilize biomembranes. Polypeptides and polysaccharide derivatives act as a type of net which supports the biomembrane. Typical examples are spectrin, located at the inner surface of the erythrocyte membrane, clathrin, which is the major constituent of the coat structure in coated vesicles, and murein (peptidoglycan) a macromolecule coating the bacterial membrane as a component of the cell wall. Is it possible to mimic Nature and stabilize synthetic lipid bilayers by coating the liposome with a polymeric network without any covalent linkage between the vesicle and the polymer One can imagine different ways for the coating of liposomes with a polymer. This is illustrated below in Fig. 53. 

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