Design of Customize Interbody Fusion Cages of Ti64ELI with Gradient Porosity by Selective Laser Melting Process

Cheng-Tang Pan; Che-Hsin Lin; Ya-Kang Huang; Jason S C Jang; Hsuan-Kai Lin; Che-Nan Kuo; De-Yao Lin; Jacob C Huang

doi:10.3390/mi12030307

Design of Customize Interbody Fusion Cages of Ti64ELI with Gradient Porosity by Selective Laser Melting Process

Micromachines (Basel). 2021 Mar 15;12(3):307. doi: 10.3390/mi12030307.

Authors

Cheng-Tang Pan^{1

2}, Che-Hsin Lin¹, Ya-Kang Huang¹, Jason S C Jang^{3

4}, Hsuan-Kai Lin⁵, Che-Nan Kuo⁶, De-Yao Lin⁷, Jacob C Huang⁸

Affiliations

¹ Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung City 80424, Taiwan.
² Institute of Precision Medicine, National Sun Yat-Sen University, Kaohsiung City 80424, Taiwan.
³ Department of Mechanical Engineering, National Central University, Taoyuan City 32001, Taiwan.
⁴ Institute of Materials Science and Engineering, National Central University, Taoyuan 32001, Taiwan.
⁵ Graduate Institute of Materials Engineering, National Pingtung University of Science and Technology, Pingtung City 91201, Taiwan.
⁶ Department of Bioinformatics and Medical Engineering, Asia University, Taichung City 41354, Taiwan.
⁷ Industrial Technology Research Institute, Hsinchu 31040, Taiwan.
⁸ Hong Kong Institute for Advanced Study, Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong.

Abstract

Intervertebral fusion surgery for spinal trauma, degeneration, and deformity correction is a major vertebral reconstruction operation. For most cages, the stiffness of the cage is high enough to cause stress concentration, leading to a stress shielding effect between the vertebral bones and the cages. The stress shielding effect affects the outcome after the reconstruction surgery, easily causing damage and leading to a higher risk of reoperation. A porous structure for the spinal fusion cage can effectively reduce the stiffness to obtain more comparative strength for the surrounding tissue. In this study, an intervertebral cage with a porous gradation structure was designed for Ti64ELI alloy powders bonded by the selective laser melting (SLM) process. The medical imaging software InVesalius and 3D surface reconstruction software Geomagic Studio 12 (Raindrop Geomagic Inc., Morrisville, NC, USA) were utilized to establish the vertebra model, and ANSYS Workbench 16 (Ansys Inc., Canonsburg, PA, USA) simulation software was used to simulate the stress and strain of the motions including vertical body-weighted compression, flexion, extension, lateral bending, and rotation. The intervertebral cage with a hollow cylinder had porosity values of 80-70-60-70-80% (from center to both top side and bottom side) and had porosity values of 60-70-80 (from outside to inside). In addition, according to the contact areas between the vertebras and cages, the shape of the cages can be custom-designed. The cages underwent fatigue tests by following ASTM F2077-17. Then, mechanical property simulations of the cages were conducted for a comparison with the commercially available cages from three companies: Zimmer (Zimmer Biomet Holdings, Inc., Warsaw, IN, USA), Ulrich (Germany), and B. Braun (Germany). The results show that the stress and strain distribution of the cages are consistent with the ones of human bone, and show a uniform stress distribution, which can reduce stress concentration.

Keywords: 3D printing; Ti64ELI; cage; gradient porosity; selective laser melting; stress concentration; stress shielding.