Influence of different classes of crosslinkers on alginate polyelectrolyte nanoparticle formation, thermodynamics and characteristics

Complexation of linear alginate polyanions with different classes of crosslinkers (divalent cations, polycations, positively charged surfactants) was investigated, to unravel their effects on nanoparticle formation. The goal was to define the crosslinker-to-alginate molar ratios at which nanoparticles are formed, and to reveal the underlying thermodynamics and molecular interactions using dynamic and electrophoretic light scattering, isothermal titration calorimetry, and infrared spectroscopy. Alginate nanoparticles were formed across a limited range of molar ratios that was specific for each crosslinker, and had different size and stability. Thermodynamic parameters of alginate complexation with crosslinkers showed that nanoparticle formation was in all cases entropy driven, together with a minor enthalpic contribution. The crosslinking mechanism was based on ionic interactions, with accompanying weaker interactions specific for each crosslinker, and involved characteristic macroscopic association constants (Ka1) for complexation of alginate (range, 104-109 M−1). Additionally, the ionic strengths of the media influenced the characteristics and stabilities of the polyelectrolyte nanoparticles.