Study of the mechanical behavior and cell viability on 3D-printed Ti6Al4V surfaces: porosity optimization for intervertebral spacer design

Abstract

Additively manufactured porous titanium implants offer a promising strategy to reduce stress shielding and promote bone interaction in spinal fusion procedures. In this work, Ti-6Al-4V lattice structures fabricated by Electron Beam Melting (EBM) were evaluated as candidates for intervertebral spacer applications. Three pore sizes (0.8 , 0.9, and 1.0 mm) were designed and produced using an Additive Arcam SPECTRA L (GE, Gothenburg, Sweden), along with solid EBM and cast Ti-6Al-4V controls. The study combined structural, mechanical, and in vitro biological characterization to determine how pore size influences performance. Dimensional analysis using scanning electron microscopy and ImageJ confirmed good geometric fidelity between CAD models and as-built lattices, with the 0.9 mm configuration showing the smallest deviation in pore diameter and strut thickness. Under uniaxial compression (ASTM E9), increasing pore size reduced both strength and stiffness. The 0.9 mm lattice exhibited a maximum compressive stress of approximately 564 MPa and an apparent modulus of approximately 13.5 GPa, values closer to those of vertebral trabecular bone than to those of solid Ti-6Al-4V. Attempts to perform compression fatigue testing (ASTM E466) revealed limitations of standard displacement-based preload protocols for highly compliant lattices, highlighting the need for adapted fatigue methodologies. A separate rotational fatigue test on a solid EBM specimen confirmed the correct functioning of the fatigue equipment. Biological performance was assessed using C2C12 murine myoblasts cultured on Ti-6Al-4V discs representing each pore size. Fluorescence imaging (Phalloidin/DAPI) showed robust cell adhesion and organized cytoskeletal structures across all lattices, while Live/Dead assays demonstrated high viability (>97%) with no pore size dependent cytotoxicity. Integrating mechanical, structural, and cellular findings, the 0.9 mm lattice emerged as the promising design, offering favorable balance between biomechanical compatibility, structural integrity and early cell response for potential use in intervertebral spacer implants.