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

Lorena Emanuelli; Alireza Jam; Anton du Plessis; Carlo Lora; Raffaele De Biasi; Matteo Benedetti; Massimo Pellizzari

doi:10.18063/ijb.728

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

Int J Bioprint. 2023 Apr 5;9(4):728. doi: 10.18063/ijb.728. eCollection 2023.

Authors

Lorena Emanuelli¹, Alireza Jam², Anton du Plessis^{3

4}, Carlo Lora⁵, Raffaele De Biasi², Matteo Benedetti², Massimo Pellizzari²

Affiliations

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.

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 (ρ_r) 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: Additive manufacturing; Auxetic structure; Functionally graded porous structures; Laser powder bed fusion; Metrological characterization; Ti-21S.