AccScience Publishing / IJB / Volume 9 / Issue 4 / DOI: 10.18063/ijb.728
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RESEARCH ARTICLE

Manufacturability of functionally graded porous β-Ti21S auxetic architected biomaterials produced by laser powder bed fusion: Comparison between 2D and 3D metrological characterization

Lorena Emanuelli1* Alireza Jam2 Anton du Plessis3,4 Carlo Lora5 Raffaele De Biasi2 Matteo Benedetti2 Massimo Pellizzari2
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1 INSTM (Operative center: University of Trento), Via Sommarive 9, Trento, Italy
2 University of Trento, Department of Industrial Engineering, Trento, Italy
3 Research Group 3D Innovation, Stellenbosch University, Stellenbosch, South Africa
4 Object Research Systems, Montreal, Canada
5 SISMA SpA, Piovene Rocchette, Vicenza, Italy
(This article belongs to the Special Issue 3D Printing of Advanced Biomedical Devices)
© Invalid date by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
Abstract

Functionally graded porous structures (FGPSs) are attracting increasing interest in the manufacture of prostheses that benefit from lower stiffness and optimized pore size for osseointegration. In this work, we explore the possibility of employing FGPSs with auxetic unit cells. Their negative Poisson’s ratio was exploited to reduce the loss of connection between prosthesis and bone usually occurring in standard implant loaded under tension and therefore undergoing lateral shrinking. In addition, to further improve osseointegration and mitigate stress shielding effects, auxetic FGPSs were fabricated in this work using a novel β-Ti21S alloy characterized by a lower Young’s modulus compared to traditional α + β Ti alloys. Specifically, two different auxetic FGPSs with aspect ratio equal to 1.5 and angle θ of 15° and 25° with a relative density (ρr ) gradient of 0.34, 0.49, 0.66 and of 0.40, 0.58, 0.75 were designed and printed by laser powder bed fusion. The 2D and 3D metrological characterization of the as-manufactured structures was compared with the design. 2D metrological characterization was carried out using scanning electron microscopy analysis, while for the 3D characterization, X-ray micro-CT imaging was used. An undersizing of the pore size and strut thickness in the as-manufactured sample was observed in both auxetic FGPSs. A maximum difference in the strut thickness of −14 and −22% was obtained in the auxetic structure with θ = 15° and 25°, respectively. On the contrary, a pore undersizing of −19% and −15% was evaluated in auxetic FGPS with θ = 15° and 25°, respectively. Compression mechanical tests allowed to determine stabilized elastic modulus of around 4 GPa for both FGPSs. Homogenization method and analytical equation were used and the comparison with experimental data highlights a good agreement of around 4% and 24% for θ = 15° and 25°, respectively.

Keywords
Functionally graded porous structures
Ti-21S; Auxetic structure
Metrological characterization
Laser powder bed fusion
Additive manufacturing
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