Quantitative analysis of the geometric fidelity of human bone twins produced by additive manufacturing in hydroxyapatite and Ti-6Al-4V alloy

Abstract

Additive manufacturing (AM) opens new opportunities in producing complex shape architectures such as bone scaffolds. Bone tissue features an interconnected lattice microstructure with high porosity and thin wall thickness which are difficult to reproduce with the current AM processes spatial resolutions. This study aims at assessing the feasibility of replicating a human trabecular bone microstructure through laser powder bed fusion and vat-photopolymerization additive technologies. To this purpose, three bone samples were harvested from the tibias of fresh human cadavers and scanned through X-Ray micro-computed tomography. The microstructure of one of these samples was then mimicked using both a Ti-6Al-4V ELI (TA6V) powder and a hydroxyapatite (HA) slurry, shaped by AM processes. The as-built parts were scanned to compare their geometries with the nominal bone model at macroscopic and microscopic scales. This analysis was carried out through image processing by quantifying the dimensional deviations from the reference model on the one hand and by measuring the microstructure parameters on the other hand. Results have shown that the geometries of the TA6V and HA printed parts closely match the bone reference model with dimensional deviations up to 0.02 ± 0.07 mm and 0.06 ± 0.20 mm at scale 1:1 for TA6V and HA replicas respectively. At microscopic level, the material volume fraction of the printed parts is higher than that of the reference model, indicating that further manufacturing parameters optimizations are required to improve the processes resolutions to achieve bone trabeculae characteristic size.