Multimaterial direct 4D printing of high stiffness structures with large bending curvature

The emerging direct four dimensional (4D) printing approach is considered as an easy, fast and economical manufacturing strategy that fabricates complex 3D geometries evolving from printed flat patterns in response to external stimuli. However, its implementation to practical engineering applications is impeded by the fact that the existing direct 4D printing methods could not render both the large bending curvature and high loading capacity at the same time. Herein, we report a multimaterial direct 4D printing method to fabricate patterned laminate that consists of covalently bonded elastomer and high-water-content hydrogel. The dehydration induced large volumetric shrinkage (up to 60%) and great modulus escalation (from 100 kPa to 4 GPa) allow the printed flat patterns to evolve into complex 3D structures with large bending curvature (up to 0.7 mm) and high bending stiffness (up to 10 MPa m). To facilitate the structural design, we develop a phenomenological model to describe the dehydration induced shrinkage and stiffening, and implement this model into Euler–Bernoulli beam theory and finite element simulations. Compared with other 3D printing technologies, the proposed multimaterial direct 4D printing approach demonstrates the merits in terms of less building time and high load capacity at both room temperature and high temperature.