The integration of stiff and flexible materials in multimaterial 3D printing enables functional applications in soft robotics, wearables, and adaptive structures. However, the interfaces between mechanically dissimilar 3D-printed materials often suffer from insufficient adhesion, leading to premature debonding under load. This study addresses the low bonding strength by employing optimized printing orientations that create dense mechanical interlocking within a submillimeter zone, thereby significantly enhancing the interfacial toughness between polylactic acid (PLA) and thermoplastic polyurethane (TPU). By systematically comparing different printing orientations and interlocking designs, the results demonstrate that specimens printed “on edge” orientation exhibit up to a 389% increase in interfacial toughness compared to “flat” oriented specimens, and up to 19 times higher toughness and 17 times higher crack initiation force relative to their pristine counterparts. Microscopic analysis reveals unique interleaved, “book-like” morphological features that drive this enhancement, while mechanical testing confirms the higher resistance to delamination. These findings demonstrate that strategic selection of printing orientation combined with interfacial mechanical design provides a scalable route for achieving robust bonding between dissimilar materials in multimaterial additive manufacturing.
Farràs-Tasias et al. (Wed,) studied this question.