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

Block copolymers (PM; P₂₀M₁₀₁ and P₁₀₀M₉₈) comprising poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC, P) containing biocompatible phosphorylcholin pendants and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC, M) were synthesized via a controlled radical polymerization method. The degrees of polymerization of the PMPC and PMAPTAC segments are denoted by subscripts (PM). The mixture of cationic PM and anionic sodium chondroitin sulfate C (CS) with the pendant anionic carboxylate and sulfonate groups formed polyion complex (PIC) aggregates in phosphate-buffered saline. A charge-neutralized mixture of P₂₀M₁₀₁ with CS formed P₂₀M₁₀₁/CS PIC vesicles with a hydrodynamic radius (R_h) of 97.2 nm, zeta potential of ca. 0 mV, and aggregation number (N_agg) of 23,044. PMPC shells covered the surface of the PIC vesicles. The mixture of P₁₀₀M₉₈ and CS formed PIC spherical micelles with the PIC core and hydrophilic PMPC shells. The R_h, zeta potential, and N_agg of the PIC micelles were 26.4 nm, ca. 0 mV, and 404, respectively. At pH < 4, the carboxylate anions in CS were protonated. Thus, the charge balance in the PIC micelles shifted to decrease the core density owing to the electrostatic repulsions of the excess cations in the core. The PIC micelles dissociated at a NaCl concentration ≥0.6 M owing to the charge screening effect. The positively charged PIC micelles with excess P₁₀₀M₉₈ can encapsulate anionic dyes owing to electrostatic interaction.