Design Synthesis of a 4D-Printed Self-Tying Knot with Programmable Morphology

Abstract Smart materials provide a means with which we can create engineered mechanisms that artificially mimic the adaptability, flexibility and responsiveness found in biological systems. Previous studies have developed material-based actuators that could produce targeted shape changes. Here we extend this capability by introducing a novel computational and experimental method for design and synthesis of a material-based mechanism capable of achieving complex pre-programmed motion. By combining active and passive materials, the algorithm can encode the desired movement into the material distribution of the mechanism. We use multimaterial, multiphysics topology optimization to design a set of kinematic elements that exhibit basic bending and torsional deflection modes. We then use a genetic algorithm to optimally arrange these elements into a sequence that produces the desired motion. We also use experimental measurements to accurately characterize the angular deflection of the 3D printed kinematic elements in response to thermomechanical loading. We demonstrate this new capability by de novo design of a 3D printed self-tying knot. This method advances a new paradigm in mechanism design that could enable a new generation of material-driven machines that are lightweight, adaptable, robust to damage, and easily manufacturable by 3D printing.