Rapid Photogelation of Low‐Concentration Polymer Solutions via Photodimerization of o‐Ethylnitrobenzene

Abstract

ABSTRACT Polymers that exhibit significant property changes upon light stimulation are promising for biomaterials due to their minimally invasive nature and spatiotemporal controllability. In this study, o‐ethylnitrobenzene (ENB) was identified as an effective photocrosslinking motif and incorporated into poly(vinyl alcohol) (PVA), yielding a new class of photocrosslinkable, water‐soluble polymers. These polymers undergo rapid gelation (∼0.5 s) from dilute aqueous solutions (∼0.5 wt.%) upon UV irradiation to form flexible and elastic hydrogels. The resulting hydrogels exhibit high compressive resilience; for example, a cylindrical hydrogel prepared from a 1.5 wt.% solution withstands a compressive stress exceeding 10 MPa without fracture. Hydrogels formed from 2 wt.% solutions swell isotropically up to 200 fold in water while retaining sufficient mechanical strength for manual handling, even at a water content of 99.99 wt.%. Furthermore, the addition of the polymer to cell‐containing media, followed by photoinduced gelation in the presence of cells, preserves cell viability. Cells are instantaneously immobilized in 3D space within the hydrogel, forming a highly permeable culture system that enables long‐term culture through medium exchange and promotes the formation of large cellular spheroids. These results highlight the potential of ENB‐based hydrogels for spatiotemporally controlled 3D cell culture applications.