A Review on Bio-Based Click Hydrogels Prepared by Diels-Alder Reactions

D ue to their hydrophilic network and their high ability to absorb and retain large amounts of water, hydrogels are widely used in medicine, industry, and the environment for different applications such as tissue engineering, drug delivery, and adsorption of pollutants. In addition to synthetic materials, hydrogels can be made from non-toxic, highly biocompatible, and biocompatible bio-based compounds. Recently, Diels-Alder cycloaddition reaction has been used to produce hydrogels with improved properties. Following Diels-Alder reaction, a six-membered ring is formed by the [4+2] cycloaddition between an electron-rich diene and an electron-deficient dienophile. To perform this reaction, no catalyst is required, and moreover no by-products are produced. Other important features of Diels-Alder reactions include insensitivity to various functional groups and thermal reversibility through retro-Diels-Alder reaction. However, by using the Diels-Alder reaction, it is possible to produce biocompatible bio-based hydrogels with an enhanced performance like stimulus-responsivity, self-healing property, and in-situ forming ability for a variety of applications. In this article, after a brief review of hydrogels and click reactions, recent studies and their objectives for the preparation of various biobased hydrogels using Dils-Alder reactions are discussed.