Hydrogels formed by the crosslinking of macromolecular precursors are used in a wide range of applications from drug delivery depots to cell culture scaffolds. In the context of cell-laden scaffolds, the utility of the hydrogel often hinges on its ability to be degraded. Degradation can be achieved through bulk hydrolysis, enzymatic action, or photolysis. Photodegradable hydrogels possess many advantages stemming from their ability to be modified in space and time in a user-defined manner, and are used to exert spatiotemporal control over crosslinking density to create local or global modifications to gel mechanics and topography.<br/>Until now, photodegradation has been achieved based on incorporation of a photoactive species directly into the polymer backbone and cleavage of that molecule. This strategy suffers from slow kinetics because a single photon can cleave, at most, a single crosslink. We have developed a hydrogel platform that can be degraded through a radical addition-fragmentation chain transfer mechanism. Upon exposure to light in the presence of a photoinitiator, rapid exchange between network allyl sulfides and free monofunctional thiols results in network degradation. The kinetics of this reaction far surpass those achieved with hydrogels that rely on alpha photocleavage of a molecule in the polymer backbone, with apparent rate constants 10-1000 times higher than these systems. This photodegradation reaction also proceeds in a cytocompatible manner, and cells remain viable through encapsulation in the AFCT hydrogel and subsequent release. Additionally, the lower concentration and decreased attenuation of photoactive species allows the degradation of much thicker samples, and we demonstrate the photodegradation of a 1 cm-thick hydrogel in under two minutes using a cytocompatible photoinitiator concentration and light dose.<br/>The utility of this hydrogel can be seen by comparing to previously reported backbone cleavage-type hydrogels, where reverse gelation is achieved in ~10 minutes for a 20 μm thick sample under the same irradiation conditions. We propose that this new photodegradation strategy will broaden the scope of photodegradable hydrogels in regenerative medicine applications.

Amplified photodegradation of cell-laden hydrogels through an addition-fragmentation reaction

253rd National Meeting (2017)

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