Fabrication of mechanically tough and highly stretchable hydrogel from orange peel derived pectin

Abstract

Pectin is a high molecular weight naturalpolysaccharide. Ittypically forms hydrogel with weak mechanical strength compared to available synthetic polymeric hydrogels, which has limit various biomedical applications of it. Considering these, here we have developed a new pectin-based cross-linker (PBC) and took use of its functionality to improve the toughness and stretchability of an acrylic acid (PAA) hydrogel. To do so, de-esterification of orange peel derived pectin was performed via saponification. PBC was prepared by coupling DP with 2-aminoethylmethaacrylate hydrochloride (AEM) with the help of N-Hydroxysuccinimide (NHS) utilizing EDC coupling procedure. Pectin, DP and PBC were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and 1H Nuclear Magnetic Resonance Spectroscopy (1H-NMR). Pectin-based hydrogels were prepared by free radical polymerization reaction of AA with PBC in the presence of potassium persulphate (KPS) initiator. Surface morphology of the prepared hydrogel (PAA-PBC-0.3%) was analysed by Scanning Electron Microscopic (SEM) technique, which revealed rough surface along with micro spaces for water absorption. Following successful incorporation of PBC into the AA hydrogel,neat hydrogels of PAA, PAA-MBA-0.3%, PAA-DP-0.3%, PAA-PBC-0.1%, PAA-PBC-0.2%, PAA-PBC-0.3%, and PAA-PBC-0.5% were produced for comparison and the mechanical characteristics of prepared hydrogelswere exploredusing Universal Testing Machine (UTM).The Young’s modulus and toughness of the hydrogels were evaluated from the stress-strain curves.It was clearly observed that thetoughness value just augmentedfrom 1163 kJ/m3to 4830kJ/m3with the increases in the cross-linker percentage from 0.1 to 0.3, which indicate that the number of covalent crosslinking points increases with an increase in cross-linker percentages.However, it was only 164kJ/m3and 445kJ/m3for the incorporation of commercial cross-linker MBA (0.3%) and DP (0.3%) respectively.Furthermore, it was observed that the equilibrium swelling capacity of PAA hydrogels was reduced as PBC cross-linker content increased from 0.1% to 0.5%. In conclusion, the facile technique to attain a new type of cross-linker PBC, and PBC incorporated PAA hydrogels with improved mechanical performances broaden the practical applications of hydrogel materials.