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

Abstract

Smart materials provide a means by 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.