Multivalent Cation-Triggered Folding of Hydrogel Sheets

Self-folding gels have been created for purposes such as drug delivery, biosensing, and tissue scaffolding. These gels typically exhibit short-side folding, i.e. folding occurs about an axis parallel to the short side of the rectangle. The only examples of long-side folding in gels involve applying a constraint, such as clamping the gel to introduce a bias. In this project, we report the fabrication of a self-folding hydrogel sheet that transforms from a flat sheet to a tube, via long-side folding, and characterize this folding behavior. We believe that long-side folding occurs due to the nonhomogenous stresses as crosslinking of the gel occurs to initiate folding. The bilayer consists of two components, one of which interacts with multivalent cations such that the swelling ratio is affected to create differential swelling. We explore the behavior of folding in response to various multivalent cation solutions and the concentration of a biopolymer. These parameters allow us to tune the folding axis and tightness of the curled structure. Long-side folding opens up more possibilities in 3-D structures that bilayer gels are able to fold into. The stimulus of cations is also important for biomedical applications, especially if the gel can be optimized to respond to physiological concentrations.