Numerical comparison of lattice unit cell designs for medical implants by additive manufacturing

ABSTRACT

The aim of this study was to compare traditional strut-based lattices with minimal surface designs using morphological analysis and image-based simulations of design files. While the two types have been studied widely, no direct comparison has ever been done. Surprisingly, there are no major differences in performance between the two types generally, but minimal surface designs do outperform slightly on angular load simulation. However, minimal surface designs in this density range are shown to have very thin walls, potentially making their accurate production more challenging, or more suitable for applications where larger pore sizes and sheet thicknesses may be applicable. Interesting results such as dual pore size distributions and variations in tortuosity of pore networks are demonstrated, with differences between various designs. The results show that all the tested designs are suitable for bone implants, but the best design might be selected based on its specialised performance requirements.

KEYWORDS:

• Lattice structures
• additive manufacturing
• bone implants
• geometric design

Acknowledgements

Johannes Fieres is acknowledged for assisting in setting up the distributed computing capability to allow the structural mechanics simulations on these large data sets. Models for minimal surface designs were obtained from Karel Lietaert (3D Systems) and Mohammad Ahmadi (Biomechanical Department of the TU Delft) and they are acknowledged for sharing these files. We also acknowledge Materialise for providing a temporary license of the Magics software to produce models for strut-based designs.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Prof. A du Plessis is Associate Professor at Stellenbosch University. His research interests lie in applications of X-ray microCT, additive manufacturing and biological structures (specifically biomimicry). He has published 80 journal papers.

Dr. I Yadroitsava is currently Senior Researcher at Faculty of Engineering and Information Technology, Central University of Technology, Free State. Since 2010, her specific focus and area of research interest are in Additive Manufacturing. She is co-author of more than 40 papers in this field.

Prof. I Yadroitsev is Research Professor at Faculty of Engineering and Information Technology, Central University of Technology, Free State. In 2015, he was appointed as SARChI Research Chair in Medical Product Development through Additive Manufacturing. Prof. Yadroitsev has over 30 years of academic experience in Applied Optics & Laser technologies (additive manufacturing, laser processing, material science, and optics). He has strong interdisciplinary background and extensive experience in the field of Physics and Engineering. He published more than 140 papers and he is a holder of 11 patents.

Mr. SG le Roux is Researcher at the Stellenbosch University CT facility. His main expertise is image analysis of X-ray microCT scans. He has published 30 journal papers.

Prof. DC Blaine is Associate Professor in Mechanical Engineering, with research interest primarily in Materials Engineering, with a specific focus on powder metallurgy (PM) and the mechanical behaviour of materials. Her current research projects focus on process modelling for PM manufacturing as well as the development and characterisation of PM materials. She has supervised several postgraduate students, published 50 papers and regularly presents her research at international conferences.e

ORCID

A du Plessis http://orcid.org/0000-0002-4370-8661

Additional information

Funding

This work is based on research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Grant No. 97994) and the Collaborative Program in Additive Manufacturing (Contract No. CSIR-NLCCPAM-15-MOA-CUT-01).