Swelling-induced surface instability patterns guided by pre-introduced structures

Swelling-induced, spontaneously generated surface instability patterns in substrate-attached hydrogel films can be harnessed for advanced applications, however, methods to control their formation and morphology are missing. Here we propose that their generation may be guided by intentionally pre-introduced line structures. While uniform gel films produce irregular polygonal instability patterns, instability patterns generated in pre-patterned films with hexagonal line structures are regular hexagons with long-range order. The pre-introduced line structures act as defects in the generation of the surface instability patterns, which determine the position of the creases, regulate their rearrangement and determine their final morphology. The contrast between the pre-introduced structures and the surrounding area should be high enough for the pre-introduced structures to act as defects. Only when the characteristic wavelength of the pre-introduced pattern matches with the one of the gel film, perfect hexagonal patterns can be obtained. The gel films with uniform topographic features may find various advanced applications.