(15b) Development of a Hydrolytically Degradable PEG Hydrogel with Tunable Degradability and Solute Release

A degradable poly(ethylene glycol) (PEG) hydrogel with tunable physical properties is developed. A 3D scaffold is made by covalently cross-linking 4-arm PEG vinyl sulfone and PEG-dithiol ester. The hydrogel is then characterized in terms of degradation time and diffusion profiles and aimed towards solute delivery applications. This is one of the few degradable PEG-based scaffolds that does not utilize copolymers (e.g. PEG-polylactic acid), rely on UV exposure for polymerization (PEG-diacrylate), or have a non-specific cross-linking chemistry (PEG-amine). The hydrogel is biocompatible, inert, and has tunable mechanical properties. Protein diffusion from hydrogels is greatly influenced by the degradability of the polymer, the mesh size of the network, and the solute size. Therefore, the focus of our characterization is on these three parameters.

The degradability of the hydrogel is controlled by three distinct strategies: by varying the molecular weight of the cross-linker, by varying polymer density, and by using cross-linkers with different numbers of methylene groups between the ester and thiol groups. It should be noted that degradation gradually increases the mesh size and decreases stiffness until the network is highly disrupted and the degradation complete. Thus the change of mesh size is monitored continuously. The change in mechanical properties (i.e., shear modulus) and the solute release are also tested as a function of degradation time. Furthermore, three solutes of different molecular weight are used to test the dependence of solute release on the size of the solute.

The developed degradable hydrogel has a variety of applications in the area of drug delivery and tissue engineering due to its unique properties, tunability, and ability to form 3D matrices under physiological conditions.