Polymer Membrane Tensegrity: Inverse Design of Polymer Films Morphing into Freeform 3D Surfaces with Digital Photopatterning Technique
In Metamorphosis of Plants (1790), Goethe traced diverse plant organs to transformations of a common leaf-like structure -- a principle modern mechanics attributes to two material ingredients: non-uniform in-plane strain from differential growth or shrinkage, and spatially patterned stiffness. Here we translate this principle into a synthetic fabrication framework called Polymer Membrane Tensegrity (PMT). A flat elastomeric film swollen with a second monomer is selectively UV-cured through a liquid-crystal display (LCD) photomask in a single-side digital photopatterning step, producing rigid rods embedded in a soft, shrinkable membrane. After the unreacted monomer is extracted with a solvent and the film is dried, the membrane shrinks far more than the rods, generating a ~50% in-plane strain differential and a ~2,000-fold modulus contrast -- conditions under which the contracting membrane is held in tension by mutually unconnected rods, a tensegrity-inspired arrangement within a single film. An origami-based inverse design algorithm computes the rod layout that morphs the film into a prescribed 3D surface. We demonstrate PMT on a dome, a hyperbolic surface, and a gyroid unit cell -- positively and negatively curved targets -- reproducing all three with mean deviations of 1.0-2.1% of the target size; perimeter curve optimization halves the mean deviation of the gyroid. Because patterning occurs on one side only, PMT eliminates the front-to-back alignment demanded by bilayer methods, offering a scalable route from flat polymer films to freeform 3D surfaces.