Photodegradation actuated shape‐changing hydrogels

Abstract

Hydrogels are attractive materials for generating 4D shapes due to their ability to undergo pronounced volume changes in response to several stimuli, including light. We previously reported shape-changing hydrogels actuated by longwave UV and visible light in the presence of live cells using poly(ethylene glycol) macromers incorporating different photodegradable ortho-nitrobenzyl (o-NB) groups. In this comprehensive study, we determine the effect of chemical structure of different o-NB macromers (which influences molar absorptivity and rate constant of degradation), composition (macromer weight percent), fabrication design (initial gel thickness) and environment (ionic strength of solution) on light-induced hydrogel folding. We demonstrate successful photopolymerization and subsequent photodegradation of hydrogels, multistep folding, and live-cell encapsulation. This hydrogel system may be useful as new tool in stem cell differentiation and developmental biology research, facilitating the in vitro investigation of processes that are sensitive to both physical and temporal stimuli.

Fabrication of Photoprocessable Materials via Photopolymerization Using an Acid‐Induced Photocleavable Platinum‐Acetylide Crosslinker

“…Photoprocessable moieties that react only under high irradiation intensities, long irradiation times, and non-overlapping excitation wavelengths have been designed for being compatible with photopolymerization. [29][30][31][32][33][34][35][36] However, methods for designing such materials limit the available wavelengths for photoprocessing and exclude photoreactive moieties that react rapidly under weak light irradiation. Directly over- coming this problem would advance the design and utility of photocontrollable materials, including the photo-molding of photodegradable materials and the fabrication of photoadhesives that are detachable via photodegradation.…”

“…To overcome this issue, the photoprocessable moieties should remain intact during photopolymerization. Photoprocessable moieties that react only under high irradiation intensities, long irradiation times, and non‐overlapping excitation wavelengths have been designed for being compatible with photopolymerization [29–36] . However, methods for designing such materials limit the available wavelengths for photoprocessing and exclude photoreactive moieties that react rapidly under weak light irradiation.…”

Gelation Dynamics during Photo-Cross-Linking of Polymer Nanocomposite Hydrogels

“…Advances in photo-cross-linking have broadened the use of polymer hydrogels as tissue engineering scaffolds, − antifouling surfaces, − and photonic materials. − Polymer hydrogels are versatile materials comprising cross-linked polymer networks that are swollen in water. Polymer network formation by photo-cross-linking offers several advantages over conventional approaches such as thermal or redox-initiated cross-linking: it proceeds under mild reaction conditions including ambient temperature and moderate pH, and it enables spatiotemporal control upon tuning light intensity, exposure time, and illumination area. , This control is often leveraged to build complex hydrogel structures through additive manufacturing, , tunable photodegradation, − or surface patterning. − …”