A sheet of paper that gets wet and then dries becomes warped, with edges lifting. No one controls this movement, but it happens because some parts of the sheet shrink more than others. Scientists have learned to harness this effect so that a flat film folds itself into a desired 3D shape: a dome, a saddle, or even a complex gyroid cell.
After drying, the membrane shrinks by almost half, while the rods barely change in size. The membrane stretches over the rods like a tent over a frame, and the flat sheet transforms into a 3D shape. Previously, it was unclear whether such a pattern could be calculated in advance to achieve exactly the desired shape. Now it's clear: it can, and an ordinary LCD printer is sufficient.
The precision is astonishing: deviations from the desired shape are only 1–2% of its size. This means flat blanks could be folded into lightweight structures, robot parts, or surfaces resembling natural ones. And if the membrane is replaced with a material that responds to humidity, the transformation becomes reversible: the film could be stored flat and unfolded when needed.
Goethe, in 'The Metamorphosis of Plants' (1790), suggested that all plant organs are modified leaves. Modern mechanics confirms: the shape of an organ is determined by inhomogeneous deformation and stiffness patterns, and it is precisely this principle that is reproduced in the polymer film.
The idea of a flat sheet that folds itself into a complex three-dimensional shape according to a programmed pattern resonates with 'smart matter' from science fiction, such as the programmable materials in Neal Stephenson's 'The Diamond Age' or the deployable structures in the series 'The Expanse'.