Mechanical and permeability properties of SLM-formed Ti6Al4V gradient Voronoi-TPMS porous scaffolds

Single-topology porous bone scaffolds suffer from insufficient biomimetic performance and conflicting mechanical and permeability properties. To address these challenges, we present a novel radial gradient hybrid porous scaffold (RGHPS) combining a stiff outer TPMS Diamond lattice and a biomimetic inner Voronoi structure. Ti6Al4V samples with an average porosity of 53% were fabricated via selective laser melting (SLM), including three RGHPS variants with distinct gradient differences and a single Voronoi scaffold (V53) as a control. Forming quality, permeability, and mechanical properties were systematically characterized. All scaffolds show high forming fidelity with porosity error < 6%. RGHPS exhibit significantly higher permeability than V53; notably, the highest-gradient VD80 achieves 200.36% higher simulated permeability and 244.09% higher experimental permeability compared to V53. The mechanical properties of RGHPS improve with increasing gradient difference, with elastic modulus of 3.55–4.11 GPa and yield strength of 140–167 MPa, both matching human bone. RGHPS undergo gradual layer-by-layer collapse without through-going 45° shear bands during compression; by contrast, the homogeneous V53 scaffold possesses a limited elastic interval and tends to generate penetrating shear cracks under axial load. Among the tested designs, VD80 achieved a relatively balanced performance between mechanical properties and permeability, suggesting its potential as a design strategy for bone tissue engineering scaffolds.