Radical-Mediated Degradation of Thiol-Maleimide Hydrogels

Michael addition between thiol- and maleimide-functionalized molecules is a long-standing approach used for bioconjugation, hydrogel crosslinking, and the functionalization of other advanced materials. While the simplicity of this chemistry enables facile synthesis of hydrogels, network degradation is also desirable in many instances. Here, the susceptibility of thiol-maleimide bonds to radical-mediated degradation is reported. Irreversible degradation in crosslinked materials is demonstrated using photoinitiated and chemically initiated radicals in hydrogels and linear polymers. The extent of degradation is shown to be dependent on initiator concentration. Using a model linear polymer system, the radical-mediated mechanism of degradation is elucidated, in which the thiosuccinimide crosslink is converted to a succinimide and a new thioether formed with an initiator fragment. Using laser stereolithography, high-fidelity spatiotemporal control over degradation in crosslinked gels is demonstrated. Ultimately, this work establishes a platform for controllable, radical-mediated degradation in thiol-maleimide hydrogels, further expanding their versatility as functional materials. Thiol-maleimide Michael addition reactions are often employed in the synthesis of hydrogels. In this work, radical-mediated degradation of the Michael adducts formed between thiol and maleimide-functionalized poly(ethylene glycol) macromers is reported. Using both redox- and photo-initiated radicals, this common hydrogel formulation is shown to have rapid and spatiotemporally tunable degradability. image