Swelling behavior of gelatin/dextran hydrogel crosslinked by Diels-Alder click chemistry

Hydrogels are three-dimensional network of hydrophilic polymers which are widely used in biomedical applications, such as tissue engineering, regenerative medicine, cellular immobilization, and drug delivery systems. The hydrogels could be chemically crosslinked or molecularly tangled, through ionic, hydrophobic and/or H-bonding interactions. However, most of the synthetic routes to promote chemical crosslinking in hydrogels use initiators and the sub-products of the reaction may introduce toxicity into the platform (1,2). In the last decade, the click reaction emerges as an alternative of crosslinking due to high selectivity and reactivity. In the present work, gelatin and dextran were derivatized to further chemical crosslinking by Diels- Alder click reaction to study the swelling properties in different media. The derivatization reaction was confirmed by 1H-NMR spectroscopy, which the peak at 6.28 ppm correspond to the maleimide group grafted on gelatin and the protons of furoic acid could be observed at 6.64, 7.26 and 7.72 ppm in dextran sample. The swelling property of Diels-Alder hydrogel was evaluated in water, phosphate buffer solution (PBS pH 7.4) and gastric fluid simulated (GFS pH 2.0). In water the hydrogel swells 377%, while in PBS and GFS the swelling capacities were 458% and 641%, respectively. This behavior could be attributed to surface charges of the polymer chains according to pH of solution medium. The swelling mechanism was studied based on Peppas equation (3), which results in non-Fickinian mechanism, where the diffusion and relaxation of the polymer chain occur simultaneously.