Triply periodic minimal surfaces based I-graph wrapped package/primitive lattice structures: New designs,mechanical performance,and fluidic characteristics

Abstract

Triply periodic minimal surfaces (TPMS) lattice structures are gaining attention for customizable scaffolds in bone tissue engineering due to their tunable mechanical and fluidic behavior. In the present work, I-graph wrapped package (IWP)/primitive TPMS were adopted and comparatively analyzed in uniform, functionally graded, and multi-geometry hybrid (MGH) graded designs. Three gradient patterns: cell size (L, 3.17–6.35 mm), relative density (RD, 0.10–0.30), and MGH with distinct gradients (sinusoidal/circular) were proposed, resulting in complex structures with varied pore size/wall thickness. All structures were fabricated using polylactic acid via stereolithography and examined through compression testing and CFD analysis to assess their mechanical performance and fluidic behavior. Functionally graded structures reported the highest yield strength (4.91–20.33 MPa), followed by MGH (11.34–17.35 MPa) and uniform lattices (5.3 ± 9.7 MPa). Deformation progressed from bulging to densified bending in uniform structures, surface deformation to splitting collapse in graded structures, and apparent bulging with pore widening to layer fracture in MGH structures. Moreover, the RD graded structures exhibited the highest surface-to-volume ratio (S/V, 6–8 mm²/mm³), exceeding L graded structures by 40%–54% and the uniform structures by 7%–19%, whereas the IWPrime MGH graded structure exhibited the highest S/V ratio of 8.5 mm²/mm³. Similarly, permeability was also reported highest (18.3–18.7 × 10⁻⁸ m²) in graded structures (L_Primitive, RD_Primitive), outperforming uniform (14.3 × 10⁻⁸ m²) and MGH structures (12 × 10⁻⁸ m²). Although WSS ranged widely (1.10–160.47 MPa), the MGH structure showed the most variability (0.60–0.95 coefficient of variation, 0.83 skewness), likely due to their combined geometric complexity.