Dual-gel 4D Printing of Bioinspired Tubes.

The distribution of periodic patterns of materials with radial or bilateral symmetry is a universal biological design principle. Amongst the many biological forms, tubular shapes are a common motif in many organisms, and they are also important for bioimplants and soft robots. However, the simple design principle of strategic placement of 3D-printed segments of swelling and non-swelling materials to achieve widely different functionality has yet to be demonstrated. Here, we report the design, fabrication, and characterization of segmented 3D printed gel tubes composed of an active thermally responsive swelling gel (poly N-isopropylacrylamide; pNIPAM) and a passive thermally non-responsive gel (polyacrylamide; pAAM). Using finite element simulations and experiments, we detail the variety of shape changes including uniaxial elongation, radial expansion, bending, and gripping based on different segmented patterns of the two gels. Actualization and characterization of thermally induced shape changes are of key importance to robotics and biomedical engineering. Our studies present rational approaches to engineer complex material and spatial parameters with a high level of customization and tunability for additive manufacturing of dynamic gel structures.