The influence of the chemical and structural features of xylan on the physical properties of its derived hydrogels

Abstract

Xylan polysacccharides, both with and without acetyl substituents, were obtained from the specific hardwood Eucalyptus urograndis by controlled extraction processes and eventually post-acetylated. They were subsequently functionalized with well-defined levels of methacrylic monomers to thereby provide different degrees of substitution of the functional group. These modified xylans were the basis to successfully prepare for the first time xylan/poly(2-hydroxyethyl methacrylate)-based hydrogels via the radical polymerization of HEMA, used as a crosslinking agent. The tuning of the crosslinking density of the hydrogel network was accomplished by preparing hydrogels that had two composition ratios of xylan to HEMA (60 : 40 and 40 : 60) and was also done by varying the degrees of substitution. The resulting hydrogels were characterized according to their morphology, swelling and rheological properties by field emission scanning electron microscopy (FE-SEM), gravimetric measurements after immersion in water, and dynamical mechanical analysis. Surprisingly, the presence of acetyl moieties leads to stiffer hydrogels which have a reduced capacity for water uptake. A natural extension to the synthesis and characterization of the novel-based xylan hydrogels is examining one of their primary functionalities: encapsulation and release. This functionality was one of the drivers of this work when it was conceived given the inherent ability of hydrogels to act as cargo carriers. Therefore, a representative anticancer drug doxorubicin was loaded into these hydrogels and its release in different media was studied. Acetylated xylans showed high delivery ratios while non-acetylated samples leveled off at half the level of the acetylated samples.