Temperature sensitization of liposomes by use of N-isopropylacrylamide copolymers with varying transition endotherms.
Three kinds of copolymers of N-isopropylacrylamide (NIPAM) with the same conformational transition temperature and varying transition endotherms were synthesized with N-acryloylpyrrolidine (APr), N,N-dimethylacrylamide (DMAM), and N-isopropylmethacrylamide (NIPMAM) as the comonomers. Two dodecyl groups were incorporated into the termini of these copolymers as an anchor for the fixation to a liposomal membrane. Egg yolk phosphatidylcholine liposomes having these copolymers were prepared and their temperature-sensitive contents release and association properties were investigated. While these copolymer exhibited a conformational transition at ca. 40 degrees C, DeltaH for the transition increased in the order of poly(APr-co-NIPAM) < poly(DMAM-co-NIPAM) < poly(NIPMAM-co-NIPAM). The liposomes containing poly(NIPMAM-co-NIPAM) showed a drastic release enhancement of entrapped calcein above the transition temperature, whereas the liposomes with poly(DMAM-co-NIPAM) and those with poly(APr-co-NIPAM) exhibited moderate and slight enhancement of calcein release above that temperature, respectively. On the contrary, the liposomes containing poly(APr-co-NIPAM) showed significant aggregation above the transition temperature, but the aggregation was hardly observed for the liposomes having poly(NIPMAM-co-NIPAM), indicating that poly(APr-co-NIPAM) more efficiently made the liposome surface hydrophobic. Thus, we concluded that the copolymer with a large DeltaH is suitable for obtaining functional liposomes with a temperature-sensitive contents release property, whereas the copolymer with a small DeltaH is appropriate for preparing functional liposomes with a temperature-sensitive surface property.
Yoshino
Keisuke
K
Department of Applied Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan.
Kadowaki
Atsushi
A
Takagishi
Toru
T
Kono
Kenji
K
D000178:Acrylamides / Q000032:analysis / Q000737:chemistry*; D002151:Calorimetry / Q000379:methods; D008081:Liposomes / Q000032:analysis / Q000737:chemistry*; D011108:Polymers / Q000032:analysis / Q000737:chemistry*; D013696:Temperature
D000178:Acrylamides; D008081:Liposomes; D011108:Polymers; C067295:N-isopropylacrylamide