Compressive stress-strain response of covalently crosslinked oxidized-alginate/N-succinyl-chitosan hydrogels

Novel injectable hydrogels have been formed at 37°C under physiological pH using a polymer-polymer crosslinking reaction. Three different formulations were tested. After 1-day cure time at body temperature, the elastic modulus of unswollen samples ranged between 3 and 5 kPa but after 11 additional days at 4°C exceeded the target modulus of 10 kPa. Modulus data showed good agreement with theoretical crosslink density, enabling the prediction of stiffer/faster curing gel formulations. Rubber elasticity theory provided a good fit to the experimental data up to 73% compressive true strain. Based on an analysis of modulus results, it was inferred that despite the presence of two aldehyde functional groups, only one mechanically significant crosslink can form per oxidized repeat unit on the alginate chain.