Leaf-Inspired Gaussian Cells Curve Flat Surfaces

Inspired by the cells in leaves that control leaf curvature to regulate water loss, researchers present flat panels that can morph into a stiff, complex 3D structure with a different Gaussian curvature. "This … constitutes an important milestone toward versatile morphing robotic applications," write the study's authors. Materials capable of dynamically changing shape to produce a wide range of complex three-dimensional (3D) structures have many potential applications, ranging from the design of soft-robotic devices to the design of rapidly deployable structures. However, shape morphing of surfaces poses a geometrical challenge due to the conservation of Gaussian curvature. For example, transforming a non-elastic, flat sheet into a doubly curved shape, like a dome, leads to distortions such as wrinkles or cuts. For the sheet to curve simultaneously in two directions – also known as Gaussian morphing – the in-plane distances of the sheet need to be modified. In nature, the leaves of some plants can reversibly curl in response to weather by inflating and deflating specialized bulliform cells, which can modify the in-plane metrics of the leaf, allowing it to morph into a variety of complex curves. Drawing inspiration from these peculiar plant cells, Tian Gao and colleagues designed thin panels with 3D-printed inflatable pneumatic trapezoidal channels (Gaussian cells) sandwiched between two layers of airtight fabric. Actuation of the pneumatic Gaussian cells allowed the initially flat surface to both stretch and bend simultaneously, and morph into dynamic and complex shapes with a different Gaussian curvature while maintaining mechanical stability in the appropriate geometry. "[T]he resulting robust, shape-changing surfaces bring the concept of material-machine closer to providing a large-scale and general commodity product," write Gao et al.