Determination of pore size distribution and finite element analysis of additively manufactured Ti pedicle screws using X-ray microcomputed tomography

Speaker:
Glinz, Jonathan; FH OO Forschungs und Entwicklungs GmbH; Austria

Authors:
Glinz, J.; University of Applied Sciences Upper Austria; Austria
Weissenbacher, P.; University of Applied Sciences Upper Austria; Austria
Senck, S.; University of Applied Sciences Upper Austria; Austria
Schrempf, A.; University of Applied Sciences Upper Austria; Austria
Fürst, D.; University of Applied Sciences Upper Austria; Austria
Gastinger, T.; University of Applied Sciences Upper Austria; Austria
Huskic, A.; University of Applied Sciences Upper Austria; Austria
Reiter, T.; University of Applied Sciences Upper Austria; Austria
Kastner, J.; University of Applied Sciences Upper Austria ; Austria

ID: ECNDT-0369-2018
Download: PDF
Session: CT-Applications 2
Room: G3
Date: 2018-06-13
Time: 10:50 - 11:10

Additive manufacturing is a powerful method to produce patient-specific medical implants for nearly any desired geometry. In this paper we investigate a series of 12 titanium pedicle screws manufactured by selective laser melting in relation to pore size distribution and mechanical behavior using finite element analysis (FEA). Screws were scanned using X-ray microcomputed tomography (XCT) at voxel sizes between 2.5µm and 5µm using a Nanotom 180NF (GE phoenix | X-ray).

The samples show an average porosity of 0.94% at a standard deviation of ±0.07% and an exponential distribution with 95% pores being smaller than 2.5·10-4mm³. Porosity is higher towards the head of the screw compared to its tip region. Image data suggests that pores are aligned in a grid-like pattern indicating the path of the SLM laser (ConceptLaser M2 Cusing). For this reason the extension of pores in x-, y- and z- direction was closer investigated, revealing that at the neck region the extension in z-direction is always an average of 18 ±0.74% smaller than in the xy-plane. From this it can be concluded that laser power, hatch distance, and hatch spacing has not only an effect on the absolute porosity but also on the orientation of the pores.

Since the neck of a screw is exposed to the highest stress during mechanical pull-out tests this region is investigated in more detail via FEA. The FE models are generated in MedTool (Dr.Pahr Ingenieurs eU) based on XCT data and loaded with axial forces from 100 to 600N. The obtained FEA results are compared to a solid sample of same geometry. Preliminary results show no major differences in relation to Young´s modulus but additional calculations are necessary to account for different spatial resolutions and voxel sizes.

Acknowledgements
This work is supported by the project “Com3d-XCT” (Interreg ATCZ38) funded by EFRE in the framework of the Interreg V program and the project “MetAMMI” funded by the EMPIR program.