Dependence of water uptake and morphology of hyaluronan- and alginate-based hydrogels on pH and degree of crosslinking

Hydrogels of alginate and hyaluronan with 5%, 50% and 100% crosslinking, (percentage of polysaccharide carboxylate groups involved in crosslinking) are synthesized. Crosslinking and stoichiometry were varied by appropriate addition of chloromethylpyridine iodide (CMPI) to activate the carboxylic groups. Crosslinking percentage was determined by potentiometry, i.e., titrating the free carboxylate groups of the polysaccharide. Water uptake by the gels is studied in relation to crosslinking and pH. Hydrogen bonds in the three-dimensional network, as shown by FT-IR spectroscopy, are used to explain differences in water uptake and their dependence on pH. Scanning electron microscopy (SEM) analysis of the gels is performed at different pHs and the morphologies are compared with their chemical structures. Equilibrium water uptake of AA (gray) and HA (black) gels in relation to percentage crosslinking in 0.6 M NaCl.