Hydrogels with photo-responsive mechanical properties have found broad biomedical applications, including delivering bioactive molecules, cell culture, biosensing, and tissue engineering. Here, using a photocleavable
protein, PhoCl, as the crosslinker we engineer two types of poly(
ethylene glycol)
hydrogels whose mechanical stability can be weakened or strengthened, respectively, upon visible light illumination. In the photo weakening
hydrogels, photocleavage leads to
rupture of the
protein crosslinkers, and decrease of the mechanical properties of the
hydrogels. In contrast, in the photo strengthening
hydrogels, by properly choosing the crosslinking positions, photocleavage does not
rupture the crosslinking sites but exposes additional cryptical reactive
cysteine residues. When reacting with extra
maleimide groups in the
hydrogel network, the mechanical properties of the
hydrogels can be enhanced upon light illumination. Our study indicates that photocleavable
proteins could provide more designing possibilities than the small-molecule counterparts. A proof-of-principle demonstration of spatially controlling the mechanical properties of
hydrogels was also provided.