High ionic strength-driven formation of pharmaceutically loaded alginate-chitosan films with tunable release dynamics

This work develops alginate-chitosan (Alg/Chit) polyelectrolyte complex films as pH-responsive, crosslinker-free drug delivery platforms for wound-relevant environments. Film formation was enabled by temporarily suppressing electrostatic complexation at high ionic strength using KBr, followed by salt leaching to generate transport pathways. Films prepared at different Alg/Chit ratios were evaluated by swelling in wound-relevant pH buffers (5.5, 7.2, 8.2), nitrogen sorption/desorption, FTIR, and SEM. The 1:1 Alg/Chit ratio provided the most favorable balance of mechanical integrity and pH-dependent swelling, and was selected as the optimized matrix for drug delivery studies. Porosity analysis confirmed that KBr acts as a transient porogen: salt leaching substantially increased accessible pore volume and internal surface area without markedly changing the dominant pore size, consistent with a denser pore network rather than pore widening. Two antibacterial preparations with a distinct ionic character (ethonium and ciprofloxacin) were incorporated either by entrapment during complexation or by post-formation sorption, yielding clearly different release mechanisms. Entrapped ciprofloxacin displayed sustained, pH-modulated release consistent with reversible electrostatic interactions within the matrix, whereas sorbed ciprofloxacin released rapidly from near-surface domains. Ethonium release was predominantly diffusion-controlled and sensitive to matrix relaxation. Antibacterial testing against two E. coli strains confirmed functional activity, with the strongest performance generally observed for entrapment-loaded films and effective activity also achieved with dual-drug loading. Overall, KBr-regulated complexation offers a simple route to tunable Alg/Chit films that link composition and pore architecture to pH-responsive swelling, programmable release, and antibacterial function.