Influence of lignin modifications on physically crosslinked lignin hydrogels for drug delivery applications

So far, the possibility of synthesizing hydrogels based on multiple biopolymers has been investigated, and among them lignin has proven to be one of the potentials for this purpose due to the multiple advantages it offers. However, because of its high molecular weight, steric hindrance and few reactive sites on its structure, it is sometimes necessary to improve its reactivity though chemical modifications. On the basis of previous results, two chemical modifications were selected in order to enhance almond, walnut and commercial alkaline and organosolv lignins' reactivity: a peroxidation reaction for alkaline ones and a hydroxymethylation for organosolv ones. Both reactions were confirmed by multiple techniques (i.e. FTIR, GPC and TGA). Hydrogels were synthesized from these lignins according to previous works. The high lignin waste of the synthesized hydrogels suggested that despite the modification of the lignins, just the highest molecular weight fractions reacted with the matrix polymer. Moreover, the swelling capacity of modified alkaline lignin-based hydrogels was negatively affected, whereas the one for organosolv lignin-based samples improved. The SEM micrographs explained the aforementioned, and the results from the DSC and compression tests were in accordance with them. Self-extracted quercetin loading and release studies suggested that these samples could be used for controlled drug delivery.