Investigation of the characteristics of protein adsorption on polysaccharide-based hydrogels

In this study, hydrogel beads were formed by dropping chitosan (2% w/v) and a separately prepared chitosan-clay mixture into tripolyphosphate (%2 w/v, pH 8.2). Some of the chitosan and chitosan-clay beads were separated and crosslinked with 1% (v/v) glutaraldehyde (GLA). Lyophilized hydrogel beads were used in the experimental studies. Protein adsorption properties of hydrogel beads were investigated with bovine serum albumin (BSA) selected as a model protein. Parameters such as contact time, pH, temperature, and initial BSA concentration were studied to optimize the adsorption of BSA on hydrogel beads. The hydrogels were analyzed by Fourier Transform Infrared Spectroscopy (FTIR), SEM (Scanning Electron Microscope) and TGA (Thermogravimetric Analysis). Optimization conditions for chitosan, GLA-chitosan, chitosan-clay and GLA-chitosan-clay hydrogels were found as 120 minutes of contact time, pH 5.5, 25oC and 25 mg/mL protein concentration. Adsorption isotherms, adsorption kinetics and adsorption thermodynamics were studied under the optimised conditions. The adsorption isotherms were found to be compatible with Langmuir Isotherm. Among the prepared hydrogel beads, maximum adsorption of BSA was observed in chitosan-clay hydrogels. The adsorption kinetics were found to be compatible with the pseudo-second order kinetic model. Thermodynamic calculations showed that ∆H and ∆S values were negative and ∆G value was positive. Accordingly, it was concluded that adsorption was exothermic and temperature increase had a negative effect on adsorption.