Preparation of hydrogels
The free radical polymerization is the most widely used method
to prepare hydrogels (Shinde et al., 2013; Thakur and Thakur, 2014).
In a typical hydrogel formulation, the monomer reacts with a
crosslinker to form a three dimensional crosslinked polymeric
network. The chemical structures of some commonly used monomers and crosslinkers are shown in Fig. 2. Free radical polymerization comprises three main stages: initiation, propagation, and
termination (Hasirci et al., 2011; Young and Lovell, 2011 ). In the
initiation stage, free radicals (R) are generated by the dissociation