Beyond Porosity: Topology-Dependent Mechanical Response of PLA TPMS Structures Under Bone Scaffold Design Constraints

The design of triply periodic minimal surface (TPMS) structures for bone scaffolds often relies on comparisons at fixed porosity. In extrusion-based fabrication, however, changing cell size while holding the wall thickness constant couples porosity, pore size, and cell scale. This study compared sheet-based Gyroid, Diamond, and Primitive architectures fabricated from commercial PLA + HS using fused deposition modeling. The design included 22 configurations, five specimens per configuration, a nominal wall thickness of 0.20 mm, and design porosities of 44.4–78.5%. Gravimetric measurements revealed topology-dependent deviations from the designed solid fraction but could not establish internal geometric fidelity. The apparent elastic modulus ranged from 74.30 to 605.06 MPa and first-peak compressive strength from 1.59 to 16.82 MPa. Analysis of covariance revealed significant topology-by-porosity interactions. Diamond generally exhibited the highest stiffness and strength, with its separation from Gyroid narrowing toward higher porosity. Gibson–Ashby fits captured topology-dependent stiffness scaling within the tested domain. These findings support mechanical architecture selection under common manufacturing and loading conditions, without establishing biological efficacy or the suitability of the commercial filament for implantation.