Surface Modification of Liposomes with Various Hydrophilic Polymers Bearing Hydrophobic Anchors and Their Circulation Properties

Abstract

The objective of this study was to confirm the feasibility of polymer coating of liposomes with various hydrophilic polymers bearing hydrophobic anchors (HPMC-R, PVP-R, PVA-R) for designing injectable drug carriers for passive targeting of drugs. The small unilamellar liposomes (egg phosphatidylcholine: cholesterol= 5:5, 7:3 or DMPC: DCP: cholesterol= 7:1:3 in a molar ratio) were applied to the polymer coating. The polymer coating of liposomes was carried out by mixing the liposomal suspensions with the polymer solutions (sol-mixing method) or by hydrating the lipid film with the polymer solutions followed by sonication (pre-mixing method). The formation of a thick polymer layer with HPMC-R and PVA-R on the surface of the liposomes was confirmed by comparing the particle size and zeta potential of the liposomes before and after polymer coating. The coating layer formed with PVP-R was not as thick as that of HPMC-R or PVA-R. The HPMC-R coated liposomes showed a significantly improved circulation compared to that of non-coated ones as had been observed for the PVA-R coated liposomes (previously reported), while no significant improvement was observed for the PVP-R coated ones. It was concluded that a thick and flexible coating layer on the surface of liposomes with HPMC-R or PVA-R could prolong the circulation time of the liposomes and that PVP-R could not form such a steric coating layer owing to its molecular structure.