Pectin/chitosan covalent crosslinked hydrogels with carboxylic acids esters for drug delivery applications

Pectin-chitosan hydrogels generally exhibit low network stability and rapid release of encapsulated drugs, which limits their applications. These limitations can be addressed with efficient crosslinking strategies. This study describes the formulation of pectin-chitosan hydrogels chemically crosslinked with carboxylic acid esters for controlled drug delivery applications. Esters of succinic, maleic, and citric acids were prepared by esterification with methanol and used as effective crosslinkers for pectin and chitosan through ester and amide bond formation. The obtained hydrogels were characterized by FTIR, ¹³C NMR, swelling tests, and SEM to evaluate the effects of polymer composition and ester concentration on the properties of hydrogels and drug release behavior. Increasing the chitosan content and ester concentration increased the apparent crosslinking density, reduced swelling and improved hydrogel stability. Swelling degrees ranged from approximately 120% to 675%, depending on the formulation. Notably, the hydrogel prepared with a pectin-chitosan mass ratio of 1:1 and 90 mM dimethyl succinate exhibited a swelling degree of 305% and drug release exceeding 90% within 48 h. Among all the tested compositions, this formulation's drug release profile showed the best fit to the Korsmeyer-Peppas model (R² = 0.9875), indicating a diffusion-controlled release mechanism. The results demonstrate that ester-based covalent crosslinking is a simple yet versatile method for fabricating pectin-chitosan hydrogels with tunable properties. Their adjustable swelling degree and release profile highlight their potential use as drug delivery systems and in broader biomedical applications.