Chitosan solubility in organic acid solutions under ultrasonication: A comparative perspective

Chitosan, a biopolymer derived from chitin, has broad biomedical, pharmaceutical, and environmental potential but is limited by poor solubility in neutral solvents. This study systematically compares the solubility and stability of chitosan in three biocompatible organic acids-acetic acid (AA), citric acid (CA), and glutamic acid (GA)-under ultrasonication. The influence of acid type and concentration (0.2-1.0 % v/v) on dissolution efficiency, colloidal stability, and structural integrity was investigated using Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, pH measurement, zeta potential, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Results showed that AA provided the most efficient solubilization, yielding homogeneous and transparent dispersions, while CA offered superior long-term stability but induced partial ionic crosslinking at higher concentrations. GA displayed limited effectiveness, with persistent aggregation attributed to its zwitterionic nature. Ultrasonication significantly enhanced dispersion across all systems, particularly in AA, by reducing particle size and improving homogeneity. This work presents the first direct comparative evaluation of chitosan solubility in mono-, tri-, and zwitterionic acid media under identical sonication conditions. The findings establish mechanistic links between acid chemistry, ultrasonic treatment, and solubility outcomes, providing a practical framework for designing tailored chitosan formulations. Potential applications include drug-delivery systems, antimicrobial food coatings, and environmentally friendly adsorbents.