Hyaluronic Acid/Chitosan Coacervate-Based Scaffolds

Chitosan-chloride (CHI) and sodium hyaluronate (HA), two semiflexible biopolymers, self-assemble to form nonstoichiometric coacervates. The effect of counterions was briefly investigated by preparing HA/CHI coacervates in either CaCl₂ or NaCl solutions to find only a small difference in their tendency to coacervate. Higher water content in coacervates within CaCl₂ was attributed to the chaotropic nature of Ca²⁺ ions. This effect was also evidenced with smaller pore sizes for coacervates in NaCl. Besides, for coacervation of chitosan-glutamate (CHI-G) with HA, dynamic light scattering at different charge ratios indicated a wider coacervation region for the HA/CHI-G pair than the HA/CHI. This was attributed to the chaotropic and "soft" ion nature of glutamate compared to chloride as a counterion of chitosan. Positive zeta potential values for both coacervate suspensions were explained by the contribution of charge mismatch, chain semiflexibility, and intra- and intercomplex disproportionation. Finally, HA/CHI coacervates were used to encapsulate bone marrow stem cells. While cell viabilities in HA/CHI coacervates were remarkable up to 21 days, their well-spread morphology has proved that HA/CHI coacervates are promising scaffolds for cartilage tissue engineering.