Degradation, swelling, and drug release behavior of injectable ETTMP/PEGDA hydrogels

The erosion and drug release behavior of an injectable hydrogel composed of ethoxylated trimethylolpropane tri-3-mercaptopropionate (ETTMP) and poly(ethylene glycol) diacrylate were determined under physiological conditions. Water and polymer mass changes were monitored over time to characterize the swelling/deswelling and erosion of the hydrogel tablets. Experimental data were collected for hydrogels with varying polymer fractions. These data were used to develop an empirical model to predict the eroding mass change and equilibrium water content across different compositions. Three easily detectable model drugs (methylene blue (MB), sulforhodamine 101, and chloroquine) were loaded into 25, 35, and 50 wt% polymer hydrogels to understand their drug release behavior. The gelation time and time for total drug release were dependent on the weight fraction of the polymer in the hydrogel and varied with the pH of the drug solutions, with more acidic drugs increasing gelation time. Complete drug release was not observed for MB because of the reaction with ETTMP thiol groups, demonstrating the importance of understanding the potential interactions between the drug and polymer. Drug-loaded hydrogels were also monitored for erosion and were found to swell more than their neat counterparts for all drugs tested, suggesting an effect of drug loading on the extent of hydrogel crosslinking.