Poly(4-vinylpyridine)-coated liposomes: Stability studies and release of acetylsalicylic acid

Abstract

Liposomes of dimyristoylphosphatidylcholine (DMPC) and dicetylphosphate (DCP) reacted with 4-vinylpyridine (4-VP) to form a salt and, subsequently, autopolymerized for form poly(4-vinylpyridine) (poly(4-VP))-coated liposomes. The conditions for optimization of polymer coating have been determined; also, the effects of polymer coating on liposome stability, the encapsulation of ASA and its release kinetics have been measured. The coating efficiency was maximum at a DMPC: DCP 1: 1 mole ratio, at pH 4.0 in acetate buffer, and a polymerization time of 40min. The polymer-coated liposomes were stable in 2mM sodium cholate and 4 per cent isopropanol solutions, as determined from turbidity measurements, versus a 20–25% decrease in stability of uncoated liposomes. The encapsulation efficiency of ASA reached a maximum of 9 per cent at DMPC : DCP 1: 1 mole ratio. The release of ASA at 37°C., pH 70 was characterized by an initial fast release (85 and 63 per cent in 20min from uncoated and polymer-coated liposomes, respectively) followed by a slow, constant release rate up to 140min. Thus, autopolymerization of a polymerizable monomer at liposome surfaces represents a potentially feasible stabilization approach for liposomes exposed to sodium cholate solutions with greater retention of solute than uncoated liposomes.