Improving the Robustness of Self-folding Gel Origami

Self-folding of responsive polymer networks represents a powerful tool to form arbitrary 3D shapes from an initially flat 2D sheet. For example, our groups have previously developed trilayer polymer films that reversibly fold into complex origami designs due to swelling of a temperature-responsive hydrogel mid-layer. However, the configuration space of even very simple origami designs features multiple branches bifurcating from the flat state, meaning that self-folding structures can easily become trapped in an undesired state. Here, we evaluate two methods to avoid such misfolding. First, as suggested by Tachi and Hull (J. Mech. Robot. 2017), we design a set of driving forces that renders the flat state a local minimum along undesired geometrically allowed branches. While we find the approach to be effective for a single degree-6 vertex, this approach is inherently limited to a highly restricted set of crease patterns. Second, we seek to locally program the buckling direction of each vertex by incorporating an orthogonally-addressable (pH-sensitive) element that pre-biases the structure along the desired branch. As this approach should be applicable for generic crease patterns of high complexity, it represents an important step in the design of robustly self-folding structures.