Hydrophilic and Amphiphilic Polyethylene Glycol-Based Hydrogels with Tunable Degradability Prepared by Click Chemistry

Hydrogels with tunable degradability have potential uses in a range of applications including drug delivery and tissue scaffolds. A series of poly(ethylene glycol) (PEG) hydrogels and amphiphilic PEG-poly(trimethylene carbonate) (PTMC) hydrogels were prepared using copper-catalyzed Huisgen's 1,3-dipolar cycloaddition, or click chemistry as the coupling chemistry. The fidelity of the coupling chemistry was confirmed using Fourier transform infrared (FTIR) and H-1 magic angle spinning (MAS) NMR spectroscopy while thorough swelling and degradation studies of the hydrogels were performed to relate network structure to the physical properties. The cross-linking efficiency calculated using the Flory-Rehner equation varied from 0.90 to 0.99, which indicates that the networks are close to ideal at a molecular level. However, at the microscopic level cryogenic scanning electron microscopy (cryo-SEM) indicated that some degree of phase separation was occurring during cross-linking. At 37 degrees C and pH 7.4, the degradation rate of the hydrogels increased with decreasing cross-link density in the network. Introduction of PTMC as the cross-linker produced an amphiphilic gel with higher cross-link density and a longer degradation time. The degradability of the resultant hydrogels could thus be tuned through control of molecular weight and structure of the precursors.