title: Core-shell structure, biodegradation, and drug release behavior of poly(lactic acid)/poly(ethylene glycol) block copolymer micelles tuned by macromolecular stereostructure.
abstract: Poly(ethylene glycol)-b-poly(L-lactic acid)-b-poly(D-lactic acid) (PEG-b-PLLA-b-PDLA) stereoblock copolymers were synthesized by sequential ring-opening polymerization. Their micelle formation, precise micelle structure, biodegradation, and drug release behavior were systematically investigated and compared with the PEG-b-poly(lactic acid) (PEG-b-PLA) diblock copolymers with various PLA stereostructures and PEG-b-PLLA/PEG-b-PDLA enantiomeric mixture. Stereoblock copolymers having comparable PLLA and PDLA block lengths and enantiomerically-mixed copolymers assemble into the stereocomplexed core-shell micelles, while the isotactic and atactic PEG-b-PLA copolymers formed the homocrystalline and amorphous micelles, respectively. The PLA segments in stereoblock copolymer micelles show smaller crystallinity than those in the isotactic and enantiomerically-mixed ones, attributed to the short block length and presence of covalent junction between PLLA and PDLA blocks. As indicated by the synchrotron radiation small-angle X-ray scattering results, the stereoblock copolymer micelles have larger size, micellar aggregation number, core radius, smaller core density, and looser packing of core-forming segments than the isotactic and enantiomerically-mixed copolymer micelles. These unique structural characteristics cause the stereoblock copolymer micelles to possess higher drug loading content, slower degradation, and drug release rates.
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University , 38 Zheda Road, Hangzhou 310027, China.
authors.forename: Chenlei
authors.initials: C
authors.lastname: Ma
authors.forename: Pengju
authors.initials: P
authors.lastname: Pan
authors.forename: Guorong
authors.initials: G
authors.lastname: Shan
authors.forename: Yongzhong
authors.initials: Y
authors.lastname: Bao
authors.forename: Masahiro
authors.initials: M
authors.lastname: Fujita
authors.forename: Mizuo
authors.initials: M
authors.lastname: Maeda
mesh_terms: D002152:Calorimetry, Differential Scanning; D046911:Macromolecular Substances / Q000737:chemistry*; D008823:Micelles; D015394:Molecular Structure; D011091:Polyesters / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D012542:Scattering, Radiation
chemical_list: D046911:Macromolecular Substances; D008823:Micelles; D011091:Polyesters; C499774:polyethylene glycol-polylactide-polyethylene glycol; D011092:Polyethylene Glycols