Strategies in Improving Properties of Cellulose-Based Hydrogels for Smart Applications

Abstract

Hydrogels are three-dimensional polymeric networks that are able to absorb and retain large volumes of water. Chemical or physical crosslinks are required to avoid dissolution of the hydrophilic polymer chains into the aqueous phase. Because of their sorption capacity, super absorbing hydrogels have been extensively used as water-retaining devices, mainly in the field of personal hygiene products and in agriculture. Moreover, in recent years, the possibility to modulate their sorption capabilities by changing the external conditions (e.g., pH, ionic strength, temperature) has suggested their innovative application as smart materials, drug delivery devices, actuators, and sensors. The presence of the polyelectrolyte NaCMC in the hydrogel network provides a Donnan equilibrium with the external solution, thus modulating material’s sorption capacity in relation to the external solution ionic strength and pH. An important focus of the research in this field is the material’s biodegradability. This material was obtained by chemical crosslinking of cellulose polyelectrolyte derivatives, carboxymethylcellulose (CMC) and hydroxyethylcellulose (HEC), using small difunctional molecules as crosslinkers (divinyl sulfone, DVS) which covalently bound different polymer molecules in a 3D hydrophilic network. Among the biopolymers, cellulose is of special interest due to its abundance and, hence, easy availability. It is easily derivatized to different cellulosics which can be used to obtain functionalized hydrogel beads for ion exchange and affinity chromatography. Various cellulose derivatives having nitrogen or sulfur-containing groups have been prepared, and their metal ion absorption behavior has been examined. Metal ions are reported to partition between cellulosics and liquid phase. However, the use of cellulose as membrane material is not fully realized due to low stability and poor interactions in water. These drawbacks can be improved by crosslinking, radiation grafting, and surfactant adsorption. In the current chapter, we have focused on the smart applications of cellulose-based hydrogels including drug delivery systems, absorption behavior, and swelling mechanism and their prospects.