Aggregation and Gelation Behavior of Stereocomplexed Four-Arm PLA-PEG Copolymers Containing Neutral or Cationic...

Area of Science:

• Polymer Chemistry
• Materials Science
• Biomaterials Engineering

Background:

• Hydrogels based on poly(lactide) (PLA) and poly(ethylene glycol) (PEG) are of interest for various applications.
• Understanding the self-assembly and gelation mechanisms of these copolymers is crucial for controlling their properties.
• The chirality of polymer blocks can influence supramolecular organization and material properties.

Purpose of the Study:

• To investigate the gelation mechanisms of enantiomerically pure (PEG-PLA)2-R-(PLA-PEG)2 copolymers.
• To explore the influence of the linker molecule (R) on the self-assembly and hydrogel formation.
• To differentiate between reversible and irreversible hydrogel formation based on copolymer structure.

Main Methods:

• Preparation of four-arm (PEG-PLA)2-R-(PLA-PEG)2 copolymers with opposite PLA chirality.
• Utilized Dynamic Light Scattering (DLS), rheology, and fluorescence spectroscopy to study gelation.
• Investigated hydrogel formation in phosphate buffer saline (PBS) at pH 7.4.

Main Results:

• Mixing enantiomeric copolymers formed micellar aggregates with stereocomplexed PLA cores and PEG coronas.
• Aliphatic linkers (R) resulted in temperature-dependent reversible gelation via PEG chain entanglements above 5 wt.%.
• Cationic amine-containing linkers (R) led to thermo-irreversible hydrogels above 20 wt.%, driven by PLA stereocomplexation.

Conclusions:

• The nature of the linker (R) dictates the gelation mechanism and reversibility of PLA-PEG hydrogels.
• Stereocomplexation of PLA blocks is a key factor in forming thermo-irreversible hydrogels.
• PEG chain entanglements are responsible for reversible gelation in systems with aliphatic linkers.