title: Novel Structural Changes during Temperature-Induced Self-Assembling and Gelation of PLGA-PEG-PLGA Triblock Copolymer in Aqueous Solutions.
abstract: The thermoresponsive amphiphilic block copolymer poly(d,l-lactic acid-co-glycolic acid)-block-poly(ethylene glycol)-block-poly(d,l-lactic acid-co-glycolic acid) (PLGA-PEGn-PLGA), which exhibits a reversible temperature-induced sol-gel transition at higher polymer concentrations in aqueous solution has attached a great deal of interest because of its potential in biomedical applications. In the present work, the length of the hydrophobic PLGA blocks is kept constant, whereas the length of the hydrophilic PEG block is altered and this variation has a pronounced impact on the phase behavior of the aqueous samples and the structure of the polymer. A short PEG block promotes gelation at a low temperature, whereas a longer PEG block shifts the gelation point to higher temperature. By using a combination of turbidity, rheology, and small angle neutron scattering (SANS) methods, the authors have revealed dramatic temperature effects. In dilute solution, the SANS experiments expose asymmetric ellipsoid structures for the copolymer with the short PEG-spacer, whereas spherical core-shell structure is observed for the polymer with long PEG-spacer. In the semidilute concentration regime, SANS measurements disclose similar profiles for the two copolymers. In a broad temperature interval, the transition from spherical core-shell micelles to cylindrical structure and packing of cylinders is observed.
authors.affiliation: Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315, Oslo, Norway.
authors.forename: Neda Khameh
authors.initials: NK
authors.lastname: Khorshid
authors.affiliation: Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315, Oslo, Norway.
authors.forename: Kaizheng
authors.initials: K
authors.lastname: Zhu
authors.affiliation: Department of Physics, Institute for Energy Technology, P. O. Box 40, N-2027, Kjeller, Norway.
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Knudsen
authors.affiliation: Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315, Oslo, Norway.
authors.forename: Sara
authors.initials: S
authors.lastname: Bekhradnia
authors.affiliation: School of Pharmacy, Department of Pharmaceutics, University of Oslo, P.O. Box 1068, Blindern, N-0316, Oslo, Norway.
authors.forename: Sverre Arne
authors.initials: SA
authors.lastname: Sande
authors.affiliation: Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315, Oslo, Norway.
authors.forename: Bo
authors.initials: B
authors.lastname: Nyström
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D011092:Polyethylene Glycols / Q000737:chemistry*; D011098:Polyglactin 910 / Q000737:chemistry*; D012212:Rheology; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D020100:Hydrogels; D012996:Solutions; C528571:poly(lactic-co-glycolic acid)-polyethylene glycol-poly(lactic-co-glycolic acid); D014867:Water; D011098:Polyglactin 910; D011092:Polyethylene Glycols
keywords: SANS; ellipsoidal structures; hydrogels; temperature responsive triblock copolymer; transition to cylindrical structures