Synthesis and characterization of a pH-responsive poly(ethylene glycol)-based hydrogel: acid degradation, equilibrium swelling, and absorption kinetic characteristics

We developed a pH-responsive, hydrogel based on poly(ethylene glycol) (PEG) covalently cross-linked with acrylic acid and N',N'-dimethylacrylamide along with acid-labile groups. In the hydrogel, PEG plays a role as the key constituent. If its chains break, the polymer networks are destroyed. The pharmacological potential of these hydrogels were demonstrated by determining their water transport profile, modulus of elasticity, and cytotoxicity assay. The hydrogels showed a pseudo-Fickian behavior, a transport mechanism that occurs when the diffusion coefficient changes with the time and the swelling equilibrium is never fully reached. At pH 2, the PEG-richer hydrogels degraded and the scanning electron microscopy (SEM) images illustrated less-defined shapes than at pH 7 and 10. This morphological characteristic results of the hydrogel deconstruction owing to cleavage of ether bonds of the PEG chains unmaking its 3D polymer network. The proposed hydrogels were shown to be compatible to cells, indicating acceptable biocompatibility and an appropriate level of security for use in the biological environments. Furthermore, they showed structural changes in their polymer network in response to pH, which is an important characteristic for stimuli-triggered release of guest molecules.