Bioinspired Morphing Mechanisms for Soft Systems: A Review

Abstract

Throughout evolution, plants have developed a number of strategies to induce movement ensuring the survival and reproduction of their species. Carnivorous plants feed by trapping insects, sunflowers grow by following the sun, and pine cones control the dispersal of their seeds under optimal conditions. This comprehensive review first analyses the mechanisms responsible for these adaptive movements highlighting the need for a gradient in one of the physico-chemical properties to enable morphing. Next, the main synthetic shape-changing soft systems are presented in terms of their mechanism of action. A gradient in water-swelling, magneto-rheological properties, residual deformation, or extensibility gives hygromorphs, magnetomorphs, mechanomorphs, and baromorphs, respectively. The various morphing triggers, namely light, heat, pH, tensile stress, pressure, electric, and magnetic fields, are described. The opportunities and challenges of each system are put into perspective. This report aims to provide the reader with a toolbox for designing shape-changing materials considering the targeted trigger, as well as providing a deeper understanding of the underlying mechanisms paving the way for future discoveries.