title: Temperature sensitization of liposomes by use of thermosensitive block copolymers synthesized by living cationic polymerization: effect of copolymer chain length.
abstract: We prepared block copolymers of (2-ethoxy)ethoxyethyl vinyl ether (EOEOVE) and octadecyl vinyl ether (ODVE) with the number average molecular weights of 6900, 9300, and 16 700 by living cationic polymerization. The poly(EOEOVE) block acts as a temperature-sensitive moiety, and the poly(ODVE) block acts as an anchor moiety. We also investigated the effect of chain length of the copolymer poly(EOEOVE) block on the ability to sensitize liposomes. The copolymers underwent a coil-globule transition at approximately 36 degrees C in the presence of a membrane of egg yolk phosphatidylcholine (EYPC), detected using differential scanning calorimetry (DSC). Liposomes encapsulating calcein, a water-soluble fluorescent dye, were prepared from mixtures of dioleoylphosphatidylethanolamine, EYPC, and the copolymers. While the copolymer-modified liposomes released little calcein below 30 degrees C, release was enhanced above 35 degrees C, indicating that dehydrated copolymer chains destabilized the liposome membrane. In addition, copolymers with a longer poly(EOEOVE) block induced a more drastic enhancement of contents release in a narrow temperature region near the transition temperature of the poly(EOEOVE) block. As a result, the copolymer with an average molecular weight of 16 700 generated highly sensitive liposomes that produced rapid and dramatic release of the contents in response to temperature.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan. kono@chem.osakafu-u.ac.jp
authors.forename: Kenji
authors.initials: K
authors.lastname: Kono
authors.forename: Taishi
authors.initials: T
authors.lastname: Murakami
authors.forename: Tomohide
authors.initials: T
authors.lastname: Yoshida
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Haba
authors.forename: Shokyoku
authors.initials: S
authors.lastname: Kanaoka
authors.forename: Toru
authors.initials: T
authors.lastname: Takagishi
authors.forename: Sadahito
authors.initials: S
authors.lastname: Aoshima
mesh_terms: D004987:Ethers / Q000737:chemistry; D005452:Fluoresceins; D008081:Liposomes; D044367:Phase Transition; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013696:Temperature; D014753:Vinyl Compounds / Q000737:chemistry
chemical_list: D004987:Ethers; D005452:Fluoresceins; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D011108:Polymers; D014753:Vinyl Compounds; C487325:poly(2-ethoxyethyl vinyl ether); C007740:fluorexon