Hydrogels have traditionally been static materials that can provide physical bulk and diffusion controlled drug delivery, heading towards advanced regenerative medicine by mimicking the extracellular matrix (ECM). However, the natural ECM is neither static nor uniform and instead varies spatiotemporally in chemical and physical nature. New materials are needed that can mimic this natural complexity. By utilizing orthogonal, thiol-norbornene click chemistry our group has developed a modular hydrogel system that can be modified spatiotemporally with stimuli responsive crosslinks. To this end, a series of α,ω-thiol-terminated poly(<i>N</i>-isopropyl acrylamide) (PNIPAM) polymers were synthesized as these thermally responsive crosslinks. The PNIPAM crosslinkers reacted with a norbornene-functionalized hyaluronic acid (NorHA) through a UV-light induced thiol-norbornene reaction to yield stimuli responsive hydrogels. Upon heating above the lower critical solution temperature (LCST), the collapse of the PNIPAM chains into nanoscopic domains yielded macroscopic changes to the hydrogels as measured by the changes in size and mass loss of water. The scale of the thermal response was controlled by the length of crosslinker and the degree of crosslinking, creating hydrogels that could lose up to 40% of their mass upon heating above 37 °C, while containing a majority of hyaluronic acid. The thermal response was reversible, suggesting that these hydrogels could be used as shape memory materials. Moreover, this thermal response could be photopatterned on the micrometer-scale to yield hydrogels with thermal- and non-thermal-responsive regions.

Modular assembly of spatiotemporally patternable, stimuli responsive hydrogels

251st National Meeting (2016)

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