In situ formation and gelation mechanism of thermoresponsive stereocomplexed hydrogels upon mixing diblock and triblock poly(lactic acid)/poly(ethylene glycol) copolymers.

J Phys Chem B

State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China.

Published: May 2015

AI Article Synopsis

  • A novel gel system made from PLA/PEG copolymers shows promise for biodegradability and biocompatibility due to its rapid in situ gelation, occurring within 10 seconds after mixing.
  • The gel properties, including structure and mechanical traits, are significantly affected by the mixing ratio and the molecular weight of the PEG blocks in the copolymers.
  • The study suggests a gelation mechanism where PLA-PEG-PLA chains serve as connectors among micelles, enhancing the network through stereocomplexed crystallites that provide stability.

Article Abstract

A novel in situ formed gel system with potential biodegradability and biocompatibility is developed by mixing the diblock and triblock poly(lactic acid)/poly(ethylene glycol) (PLA/PEG) copolymers with opposite configurations of PLA blocks. In situ gelation of such system is extremely fast, which happens within 10 s after mixing. In situ gelation, gel-to-sol transition, crystalline structure, microstructures, and mechanical properties of PLA-PEG/PLA-PEG-PLA enantiomerically mixed gels are significantly influenced by the mixing ratio, degree of polymerization for PEG block in triblock (DPPEG,tri) and diblock copolymers (DPPEG,di). It is found that in situ gelation of PLA-PEG/PLA-PEG-PLA enantiomeric mixture just happen at relatively smaller PLA-PEG/PLA-PEG-PLA mass ratio and larger DPPEG,tri. Hydrodynamic diameters of PLA-PEG and PLA-PEG-PLA copolymers in dilute solution increase remarkably upon mixing, indicating the formation of bridging networks. Stereocomplexed crystallites are formed for the PLA hydrophobic domains in PLA-PEG/PLA-PEG-PLA enantiomeric mixtures. As indicated by synchrotron-radiation SAXS analysis, the enantiomeric mixture changes from a compactly to loosely aggregated structure and the intermicellar distance enhances with increasing DPPEG,tri, DPPEG,di, or PLA-PEG-PLA fraction. Gelation mechanism of PLA-PEG/PLA-PEG-PLA enantiomeric mixture is proposed, in which part of PLA-PEG-PLA chains act as the connecting bridges between star and flower-like micelles and the stereocomplexed crystallites in micelle cores act as physically cross-linked points.

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http://dx.doi.org/10.1021/acs.jpcb.5b03610DOI Listing

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