Modeling of network degradation in mixed step-chain growth polymerizations

The ability to form degradable hydrogels having controlled network structure is important for applications related to both drug delivery and tissue engineering. Although significant advances have occurred, these applications cannot reach full potential without the availability of materials with tunable degradation behavior. Here, we present novel thiol–acrylate degradable networks, which provide a simple method for forming degradable networks having specific degradation profiles. Degradable thiol–acrylate networks are formed from copolymerizing a thiol monomer with PLA-b-PEG-b-PLA based diacrylate macromers. A theoretical model has been developed to describe the kinetic chain length distribution, the bulk degradation behavior, and the reverse gelation point of these thiol–acrylate hydrogels. Varying the thiol functionality, as well as the relative stoichiometries of the thiol and acrylate functional groups, provides a facile means to control the kinetic chain length distribution and the concomitant degradation behavior of these systems. The extent of percentage mass loss of the network at the reverse gelation point is controlled from as low as 30% to as high as 95%, thereby giving the unique ability to dictate the material properties of the hydrogel before the network becomes completely soluble.