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 1H 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 °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.