Three-point bending fatigue behaviour of DIW-printed microporous titanium filaments for orthopaedic lattices

This study reports fatigue data on microporous titanium (Ti) filaments fabricated by direct ink writing (DIW) for orthopaedic applications. Compact (~6% closed porosity) and porous (~14% open porosity) variants were tested in three-point bending fatigue tests. Fractography and elasto-plastic finite-element analysis (FEA) were used to relate surface roughness and microporosity to crack path and local stress–strain fields. FEA showed equivalent plastic strain concentrating at surface valleys and reaching values up to ~50% higher in porous than in compact filaments, consistent with earlier fatigue crack initiation. Despite earlier initiation, fractography revealed crack deflection and branching induced by an interconnected micropore network, increasing crack-path tortuosity and thereby slowing long-crack (Stage II) propagation. Consequently, porous filaments tended to show higher low-cycle-fatigue resistance, whereas high-cycle fatigue lives were comparable. These filament-scale findings complement lattice-scale observations in which porous lattices exhibit superior overall fatigue resistance, consistent with the dominance of long-crack propagation at that scale. The results highlight the promise of DIW Ti with tailored open microporosity for load-bearing implants supporting early healing.