Anisotropic mechanical properties and energy absorption of TPMS structures: a comparative study of polylactic acid and thermoplastic polyurethane materials

Triply periodic minimal surface (TPMS) structures are valued for their exceptional mechanical properties and energy absorption capabilities, particularly in applications such as impact-resistant protection and biomedical implants. However, current research predominantly targets rigid materials, lacking systematic insight into how compliant thermoplastic polymers influence structural behaviour across orientations. This study addresses these gaps by investigating the material-structure-property relationship of TPMS architectures Primitive, Gyroid, and Diamond fabricated from three thermoplastic materials: polylactic acid (PLA) and two grades of thermoplastic polyurethane (TPU-95A and TPU-87A) across multiple orientations. Across all structures and directions, PLA exhibited the highest average specific energy absorption (SEA) of 8.205 ± 0.366 J/g, while TPU-95A achieved the highest crushing force efficiency (CFE) of 0.923 ± 0.059, indicating a trade-off between strength and deformation stability. Results show that gyroid structures demonstrated the most stable and consistent performance across materials and orientations, with variations in SEA and CFE confined within 16% and 3%, respectively. The P structure demonstrated strong orientation–material coupling, where the same orientation showed opposite crushing stability trends in PLA and TPU due to the differing stress path responses. These findings establish key structure–property relationships and offer design guidance for tailoring TPMS-based structures in protective and functional applications.