Macro bead formation based on polyelectrolyte complexation between long-chain polyphosphates and chitosan

Short chain polyphosphates (PP), mostly tripolyphosphates, have been extensively used in the literature for ionic gelation of polycations or simple cations. However, the literature around the use of longer chain polyphosphates is sparse. These longer chain PPs are of particular interest in biomedical applications as they are present in the human body, playing different roles including facilitating blood coagulation and bone formation. Here, we developed macro beads comprising longer PPs with a degree of polymerization of 22 utilizing a polyelectrolyte complexation reaction with chitosan (CS). A concentration of 15 mg mL(-1) was selected for both PP and CS solutions to produce the beads. To improve the diffusion of PPs into CS droplets and promote the complexation reaction in the beads, solution exchange following bead formation, injection size, sonication, and temperature were considered, though none improved the complexation of the beads significantly. However, addition of NaCl to the PP solution caused a significant change in the appearance of the beads and increased the P content of the beads from approximately 2.5 wt% to 18 wt%. ATR-FTIR showed that this increase was accompanied by the consumption of the protonated amine groups. Thermal analysis confirmed the interaction between the components through a notable shift in the exotermic peak of CS dissociation toward lower temperatures. Finally, the impact of curing time (5 min-24 h) on complexation within the beads was demonstrated using ICP, FTIR, and by visual observation. This work is one of the few studies recruiting moderately long chain PPs in a polyelectrolyte complexation strategy for bead formation and elucidates the significant factors affecting this interaction.