Comparison of polymerically stabilized PEG-grafted liposomes and physically adsorbed carboxymethylchitin and carboxymethyl/glycolchitin liposomes for biological applications.

The stabilities of two types of polymerically stabilized liposomes consisting of PEG-grafted (DSPC:CHOL:DSPE-PEG1900, 5:4:1) and physically adsorbed carboxymethylchitin (CMC) and carboxymethyl/glycolchitin (CO) are compared. The polyelectrolyte is adsorbed on positive (DSPC:CHOL:DMTAP, 5:4:1) and neutral (DSPC:CHOL, 1:1) liposomes at different molecular weights (Mw). In PBS buffer (c(s) = 154 mM, pH = 7.4) the theoretical stability ratios (W) calculated using the classical DLVO Theory, indicate that the CMC-coated vesicles and the negative liposomes (DSPC:CHOL:DMPG, 5:4:1) are highly stable (W >> 1) compared to the PEG-grafted (W = 0.9511) and CO-coated (W = 0.9550) liposomes. Meanwhile, experimentally determined values of W, prove that the PEG-grafted is the most stable suspension (W = 5.5). Computation of the theoretical values of W for liposome-red blood cell and liposome-macrophage indicates that the electrosterically stabilized suspensions and the negative liposomes are stable. Light scattering results show that the flocculation of liposomes in blood and plasma depends on polymer molecular weight, type of polyelectrolyte and surface charge of the uncoated liposome. Neutral liposomes coated with CMC of Mw = 1.01 x 10(5) and negative liposomes provide a more effective barrier to plasma macromolecular protein adsorption than the grafted PEG groups and are easy to resuspend in blood.