Printability, Mechanical Response, and Surface Integrity of MEX-Manufactured Gyroid Lattices with Uniform and Graded Cell Sizes

Triply periodic minimal surface (TPMS) gyroid lattices are promising lightweight and energy-absorbing polymer structures, but their manufacturability by material extrusion (MEX) depends strongly on cell size, grading direction, and relative density. This study investigates PLA gyroid lattices with uniform and graded cell-size configurations using initial and final cell sizes of 1, 1.5, and 2 mm and target relative densities of 10, 20, and 30%. A full-factorial design was used to construct a printability map, followed by quasi-static compression testing, areal surface-roughness characterization, and SEM observation of representative specimens. The printability results showed that low-density fine-cell configurations were most prone to incomplete wall formation and collapse, whereas the 30% relative-density group was printable for all investigated cell-size combinations. Under compression, the 30% relative-density uniform 1 mm gyroid showed the highest maximum stress among the tested configurations, while graded structures terminating in smaller cells also provided favorable load bearing and energy-absorption behavior. The plateau stability index, calculated from stress fluctuations between collapse and densification, helped distinguish stable progressive collapse from more oscillatory deformation. Surface roughness and SEM observations further indicated that smoother, more continuous wall surfaces were associated with more uniform deformation, whereas rougher and defect-rich surfaces promoted localized buckling, cracking, and brittle collapse. Overall, the results identify experimentally supported relationships between gyroid cell-size configuration, printability, surface integrity, and compressive response within the investigated PLA MEX design space.