Design and Evaluation of Alginate-Based Hydrogels for Controlled Release of Cationic and Anionic Model Compounds

Alginate-based hydrogels are well-known materials for drug delivery. However, their sensitivity towards chelators and burst release remain concerns. Polyelectrolyte coatings have been proposed to control drug release from hydrogels, but it remains unclear how the types of coating influence the release kinetics of drugs with varying ionic properties. Hence, we explored combinations of natural (chitosan, alginate) and synthetic (polyethyleneimine [PEI], polyacrylic acid [PAA]) polyelectrolytes to modulate the release kinetics of alginate-based hydrogel beads. Rhodamine B (RhB, cationic) and trypan blue (TB, anionic) were used as model drugs. PAA resulted in a less porous coating, and PEI effectively reduced swelling. While uncoated beads showed burst release, polyelectrolyte coatings slowed release to varying degrees. Chitosan+alginate and chitosan+PAA coatings showed limited impact on RhB release. In contrast, PEI+alginate and PEI+PAA coatings significantly reduced RhB release from 86% (uncoated) to 61% and 6% after 4 days, respectively. Alginate–TB displayed inherently slower release across all systems, with polymer coatings further reducing cumulative release from 49% (uncoated) to 7% in PEI+PAA-coated beads. Overall, polyelectrolyte coatings had a greater influence on the anionic payload, and PEI+PAA-coated beads emerged as promising carriers for controlled release of both cationic and anionic drugs.