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Rapid advances in digital fabrication technologies and new materials development allow for direct control and programmability of physical material transformations. By utilizing multimaterial 3D printing technologies and anisotropic material compositions, we can physically program hygroscopic materials such as wood to precisely sense and self-transform based on fluctuations in the environment. While wood remains one of the most common building materials in use today, it is still predominantly designed to be industrially standardized rather than taking advantage of its inherent anisotropic properties. This research aims to enhance wood's anisotropic and hygroscopic properties by designing and 3D printing custom wood grain structures to promote tunable selftransformation. In this article we present new methods for designing hygroscopic wood transformations and custom techniques for energy activation. A differentiated printing method promotes wood transformation solely through the design of custom-printed wood fibers. Alternatively, a multimaterial printing method allows for greater control and intensified wood transformations through the precise design of multimaterial prints composed of both synthetic wood and polymers. The presented methods, techniques, and material tests demonstrate the first successful results of differentiated printed wood for self-transforming behavior, suggesting a new approach for programmable material and responsive architectures.

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We developed biomimetic hygro-responsive composite polymer scales inspired by the reversible shape-changes of Bhutan pine ( Pinus wallichiana ) cone seed scales. The synthetic kinematic response is made possible through novel four-dimensional (4D) printing techniques with anisotropic material use, namely copolymers with embedded cellulose fibrils and ABS polymer. Multi-phase motion like the subsequent transversal and longitudinal bending deformation during desiccation of a natural pinecone scale can be structurally programmed into such printed hygromorphs. Both the natural concept generator (Bhutan pinecone scale) and the biomimetic technical structure (4D printed scale) were comparatively investigated as to their displacement and strain over time via three-dimensional digital image correlation methods. Our bioinspired prototypes can be the basis for tailored autonomous and self-sufficient flap and scale structures performing complex consecutive motions for technical applications, e.g. in architecture and soft robotics. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 3)’.