Porous quaternized chitosan microspheres for heparin adsorption: preparation, characterization, and performance

This study aimed to develop a chitosan-based separation medium for efficient and highly selective adsorption of anionic molecules. Porous chitosan microspheres (PCM) were prepared via inverse emulsion crosslinking with chitosan as raw material, and quaternized chitosan microspheres (QCM) with high positive charge density were synthesized using glycidyl trimethyl ammonium chloride (GTMAC) as the quaternizing agent. The structure of the microspheres was characterized by FTIR, SEM, BET, and particle size analysis. Using heparin as a model molecule, the adsorption thermodynamics, kinetics, selectivity, and cyclic stability of QCM were systematically investigated. The results showed that QCM exhibited regular spherical morphology with an average particle size of 359 ± 10 μm, an average pore diameter of 10.2 nm, and a quaternary ammonium content of 0.976 mmol/g. The maximum adsorption capacity of QCM for heparin reached 37.0 mg/g with an adsorption efficiency of 87.4%, significantly superior to commercial Amberlite FPA98 Cl resin. The adsorption followed both the Langmuir and Sips models, indicating predominantly monolayer adsorption with a certain degree of surface heterogeneity; the kinetics followed the pseudo-second-order kinetic model, which are likely dominated by electrostatic interactions. Thermodynamic analysis revealed that the adsorption process was spontaneous, exothermic, and accompanied by entropy decrease. At pH 7.0 and 0.5 mol/L NaCl, QCM showed excellent selectivity toward heparin and could effectively repel BSA. After five adsorption-desorption cycles, the adsorption capacity remained at 72.1% of its initial value. Featuring simple preparation, low cost, and favorable biocompatibility, QCM as a novel green mesoporous separation medium shows promising application prospects in the separation and purification of anionic biomolecules such as heparin.