Stabilization of phosphatidylserine/phosphatidylethanolamine liposomes with hydrophilic polymers having multiple "sticky feet"

The ability of three novel polymers to protect phosphatidylethanolamine/pho sphatidylserine (1:1) vesicles against calcium-induced destabilization (dye leakage) has been investigated. The polymers are a telechelic, hydrophobic ally terminated poly(ethylene glycol) (PEG), a polymer of the macromonomer PEG(8000)-lysine-stearylamide, and a hydrophobically modified poly(acrylic acid). These polymers are predominantly hydrophilic but have multiple hydro phobic moieties which serve to anchor them in the lipid bilayers. Like sing ly anchored PEG, the two PEG-based polymers were able to provide effective stabilization at concentrations sufficient to produce a polymer ''brush'' o n the liposome surface. Interestingly, the poly(acrylic acid) polymer did n ot provide full stabilization even at concentrations that should have produ ced brush coverage, possibly owing to a more expanded polymer conformation. The potential advantages of stabilization with polymers having multiple "s ticky feet'' are discussed.