Adv. Mater. (2013)


Imagine a honeycomb made from thin, rectangular elastic strips, attached to a substrate. If the strips swell, their edges buckle and — for linearly elastic strips — adopt sinusoidal profiles. The symmetry of the network then depends on the number of sinusoidal nodes on each edge. For an even number of nodes, the structure remains achiral: the handedness of neighbouring vertices alternates. An odd number of nodes (pictured) makes the cellular structure chiral.

Sun Hoon Kang and colleagues have derived a theoretical stability diagram that relates the number of nodes to the aspect ratio and differential swelling strain of the strips. They fabricated supported cellular structures from silicone rubber and epoxy resin, and then made them swell by wetting them with appropriate liquids. The chiral and achiral buckled-edge motifs developed as predicted.

The transfiguration works for different geometries (honeycomb and square lattices), and for both millimetre- and micrometre-sized edges. Defect-free patterns can be created by starting the wetting gradually from a single spot. Furthermore, the procedure is reversible, with 'unwetting' achieved through evaporation, and also reproducible: wetting a given sample again after four months produced exactly the same buckling-induced, lowered-symmetry patchwork.