Fabrication and characterization of mechanically strong hydrogel using modified nano-starch cross-linker

Abstract

Hydrogels are hydrophilic three-dimensional highly cross-linked polymer which has wide applications in a variety of fields but the inherent weak mechanical properties make them unsuitable for many practical applications. In addition, most of the cross-linker are used for the synthesis of conventional chemical hydrogels are toxic in nature and non-biodegradable. This work aim at facile fabrication of mechanically strong and biodegradable hydrogel using a chemically cross-linked nano-starch as a cross-linker. Here, we employ a uniform dispersion of nanoparticles for the synthesis of hydrogels using different amount of vinyl modified nano-starch cross-linker (MNSC). Mechanically strong hydrogel is prepared by free radical polymerization of N-isopropylacrylamide (NIPAAM) monomer in presence of MNSC as a cross-liking agent and potassium persulfate (KPS) as redox initiator. First, nano-starch particle (NSP) is synthesized from micro starch granules via acid hydrolysis. The synthesized NSP is then converted to carboxylated nano-starch particle (CNS) using 2,2,4,4-tetramethyl-1-oxyalpiperidine (TEMPO) mediated selective oxidation of NSP. MNSC cross-linker is synthesized by the coupling reaction between CNS and 2-Aminoethyl methacrylate hydrochloride (2-AEM) in presence of coupling agent N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC). The synthesized MNSC are able to act as cross-linker during free radical polymerizations of NIPAAM. The surface morphologies of NSP and MNSC are observed by the scanning electron microscopy (SEM) images. The superior mechanical properties of the hydrogels are established by the Universal Testing Machine (UTM) at room temperature. Here, MNSC-NIPA hydrogels can be prepared only by using a small amount of MNSC to overcome the inherent poor mechanical properties of the traditionally cross-linked polymeric hydrogels.