Design Synthesis of a 4D-Printed Self-Tying Knot

This technical report presents a novel computational and experimental method for the design and synthesis of a material-based mechanism capable of achieving complex pre-programmed motion. The study introduces a 4D-printed self-tying knot as a demonstration of this method, which combines active and passive materials to encode desired movements into the material distribution of the mechanism. The report details the use of multimaterial, multiphysics topology optimization to design kinematic elements that exhibit bending and torsional deformations. A genetic algorithm is employed to optimally arrange these elements into a sequence that produces the intended motion. Experimental measurements are conducted to characterize the angular deflection of the 3D-printed elements under thermomechanical loading. The findings suggest that this approach advances a new paradigm in mechanism design, potentially leading to lightweight, adaptable, and robust material-driven machines that can be easily manufactured through 3D printing.