Fatigue and biological behavior of Ti6Al4V reentrant auxetics manufactured by Laser Powder Bed Fusion

The current study investigates the biological response and fatigue behavior of reentrant Ti6Al4V metamaterials made using Laser Powder Bed Fusion (L-PBF). Finite element analysis of reentrant structures with eight different auxetic configurations was performed to determine optimal designs. Reduced maximum von Mises stress and displacement values were obtained in optimal designs with (L = 6 mm, Ѳ = 70°, t1 = 1.25 mm, t2 = 2.25 and 2.5 mm), suggesting greater structural stability. High-cycle fatigue testing revealed that the sample with t2 = 2.25 mm design displayed quicker plastic deformation and faster strain buildup under 5 kN load, whereas the sample with t2 = 2.5 mm structure showed the more stable fatigue response with less strain advancement. After 48 h, biological tests employing SaOs-2 osteoblast-like cells verified that all designs were non-cytotoxic. A higher porosity design (L = 5 mm, Ѳ = 65°, t1 = 1.5 mm, t2 = 1.25 mm) supported the greatest mineralization at 21 days, while increased (t2 = 2.5 mm) enhanced early-stage cell proliferation. Provided reentrant geometries facilitate Ti6Al4V lattices in achieving a balance among fatigue resistance, structural integrity, and biological efficacy for orthopedic implants.