Photodegradable Polyacrylamide Gels for Dynamic Control of Cell Functions

Cross-linked
polyacrylamide hydrogels are commonly used in biotechnology
and cell culture applications due to advantageous properties, such
as the precise control of material stiffness and the attachment of
cell adhesive ligands. However, the chemical and physical properties
of polyacrylamide gels cannot be altered once fabricated. Here, we
develop a photodegradable polyacrylamide gel system that allows for
a dynamic control of polyacrylamide gel stiffness with exposure to
light. Photodegradable polyacrylamide hydrogel networks are produced
by copolymerizing acrylamide and a photocleavable ortho-nitrobenzyl (o-NB) bis-acrylate cross-linker. When
the hydrogels are exposed to light, the o-NB cross-links
cleave and the stiffness of the photodegradable polyacrylamide gels
decreases. Further examination of the effect of dynamic stiffness
changes on cell behavior reveals that in situ softening
of the culture substrate leads to changes in cell behavior that are
not observed when cells are cultured on presoftened gels, indicating
that both dynamic and static mechanical environments influence cell
fate. Notably, we observe significant changes in nuclear localization
of YAP and cytoskeletal organization after in situ softening; these changes further depend on the type and concentration
of cell adhesive proteins attached to the gel surface. By incorporating
the simplicity and well-established protocols of standard polyacrylamide
gel fabrication with the dynamic control of photodegradable systems,
we can enhance the capability of polyacrylamide gels, thereby enabling
cell biologists and engineers to study more complex cellular behaviors
that were previously inaccessible using regular polyacrylamide gels.