Formation of Polyion Complex Aggregate Formed from a Cationic Block Copolymer and Anionic Polysaccharide

Area of Science:

• Polymer Chemistry
• Materials Science
• Biotechnology

Background:

• Block copolymers combining biocompatible poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC) and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC) were synthesized.
• These copolymers were designed to form polyion complex (PIC) aggregates with anionic sodium chondroitin sulfate C (CS) in aqueous solutions.

Purpose of the Study:

• To investigate the formation and characteristics of PIC aggregates, specifically vesicles and micelles, formed by PMPC-PMAPTAC block copolymers and CS.
• To explore the influence of block copolymer composition and environmental conditions (pH, salt concentration) on PIC structure and stability.
• To evaluate the potential of these PIC structures for encapsulating anionic molecules.

Main Methods:

• Controlled radical polymerization was employed to synthesize PMPC-PMAPTAC block copolymers with defined segment lengths.
• Polyion complexation was achieved by mixing cationic block copolymers with anionic CS in phosphate-buffered saline.
• Dynamic light scattering and zeta potential measurements were used to characterize the hydrodynamic radius, surface charge, and aggregation number of the formed PIC structures.

Main Results:

• A charge-neutralized mixture of P20M101 and CS formed PIC vesicles (97.2 nm hydrodynamic radius) with PMPC shells.
• A mixture of P100M98 and CS formed PIC spherical micelles (26.4 nm hydrodynamic radius) with a PIC core and PMPC corona.
• PIC micelle core density decreased at pH < 4 due to CS carboxylate protonation, and dissociation occurred at NaCl concentrations ≥0.6 M.

Conclusions:

• PMPC-PMAPTAC block copolymers effectively form PIC vesicles and micelles with CS, demonstrating tunable self-assembly based on copolymer composition.
• The pH-dependent structural changes and salt-induced dissociation highlight the responsive nature of these PIC materials.
• The ability of positively charged PIC micelles to encapsulate anionic dyes suggests potential applications in targeted delivery systems.