Controlled release and enhanced antibacterial activity of salicylic acid by hydrogen bonding with chitosan

Microcapsules of salicylic acid (SA) with chitosan were prepared by spray drying method. Various analytical methods were used to characterize the nature of microcapsules. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of intermolecular interactions between chitosan and SA. Particle size analysis showed that the average size of microcapsules ranged from 2 to 20   μm. Scanning electron microscopy (SEM) studies indicated that the microspheres were spherical and had a relatively smooth surface. Microbiological assay of antibacterial activity for SA and its microcapsules was measured using different bacterial strains. It was found that the antibacterial activity of SA was improved after the formation of microcapsules. The in vitro release profile showed that the microcapsules could control SA release from 1   h to 4   h. Kinetic studies revealed that the release pattern follows Korsmeyer–Peppas mechanism. Enhanced antibacterial activity of the SA microcapsules was attributed to the synergistic effects of intermolecular hydrogen-bonding interactions N–H⋯O and O–H⋯O C between SA and chitosan. It was also confirmed by quantum chemical calculation.