Degradation of oligo[poly(ethylene glycol) fumarate] hydrogels through stimulus-mediated pendent group cyclization

Hydrogels are of interest for a wide range of applications including drug delivery, regenerative medicine, agriculture, and personal care products. Among the water-soluble synthetic polymers that can be processed to form hydrogels, oligo[poly(ethylene glycol) fumarate] (OPF) has attracted significant attention. The degradation of OPF can be tuned to some extent based on the poly(ethylene glycol) chain length and amount of cross-linker incorporated, but the degradation is generally quite slow, occurring over several months. Here we introduce a new approach to tune and trigger the degradation of OPF. Fumarate alkenes were functionalized to introduce protected pendent amines, that after deprotection could cyclize to 6-membered lactams, thereby cleaving the polymer backbone. Using light as a model stimulus, we demonstrated that the cleavage of an o-nitrobenzyl carbamate protecting group led to more rapid polymer degradation. Remaining unfunctionalized fumarates allowed the functionalized OPF to be cross-linked, forming a hydrogel. Treatment with light led to breakdown of the hydrogels, as indicated by a substantial reduction in the compressive modulus. The functionalization and stimulus-responsive cleavage mechanism should be applicable to other stimuli, providing a versatile approach to control OPF degradation for various applications.