Figure 3 : Spatially and sequentially programmable 3D gel shapes.

From: Reversible patterning and actuation of hydrogels by electrically assisted ionoprinting

Figure 3

(a) 3-mm thick gel ionoprinted with five lines. As a result of the stresses developed during ionoprinting, the gel initially bends perpendicular to the imprinted directions (green arrow). Once immersed in EtOH (ethanol), the stiffer ionoprinted regions guide the asymmetric shrinking and reshaping of the gel structure (blue arrow). The initial shape recovers when placed in water. Scale bars, 15 and 10 mm, respectively; (b) example of a controlled shape by differential ionoprinting and subsequent time-dependent shape transformation after immersion in EtOH and EDTA, respectively. Scale bar, 5 mm. (c) a sequentially imprinted gel cube. The ionic crosslinks bind the imprints at the joints and provide a rigid frame controlling the structure during shrinking and swelling. Scale bar, 2 mm; (d) repetitive ethanol/water cycles of bending of a hydrogel strip imprinted with a single line, showing ~30% reduction in bending after ten cycles as measured by the end-to-end distance.