Novel Structural Changes during Temperature-Induced Self-Assembling and Gelation of PLGA-PEG-PLGA Triblock Copolymer in Aqueous Solutions

• Published in: Macromolecular bioscience 2016-12, Vol.16 (12), p.1838-1852
• Main Authors: Khorshid, Neda Khameh, Zhu, Kaizheng, Knudsen, Kenneth D., Bekhradnia, Sara, Sande, Sverre Arne, Nyström, Bo
• Format: Article
• Language: English
• Subjects: Acids; Biocompatible Materials - chemistry; Copolymers; ellipsoidal structures; hydrogels; Hydrogels - chemistry; Hydrophobic and Hydrophilic Interactions; Polyethylene Glycols - chemistry; Polyglactin 910 - chemistry; Polymers; Rheology; SANS; Solutions; Temperature; temperature responsive triblock copolymer; transition to cylindrical structures; Water - chemistry
• ISSN: 1616-5187; 1616-5195
• DOI: 10.1002/mabi.201600277

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. Thermo‐responsive amphiphilic block copolymers of poly(d,l‐lactic acid‐co‐glycolic acid)‐block‐poly(ethylene glycol)‐(PEG) block‐poly(d,l‐lactic acid‐co‐glycolic acid) type with different PEG length are prepared. These polymers have wide ranges of potential for biomedical applications. These copolymers exhibit very interesting structural features in both dilute and semidilute solutions. In the semidilute concentration regime, the structures change from core–shell to cylindrical shape as the temperature increases.