Femur auxetic meta-implants with tuned micromotion distribution

Ghavidelnia, N., Bodaghi, M. ORCID: 0000-0002-0707-944X and Hedayati, R., 2020. Femur auxetic meta-implants with tuned micromotion distribution. Materials, 14 (1): 114. ISSN 1996-1944

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Stress shielding and micromotions are the most significant problems occurring at the bone-implants interface due to a mismatch of their mechanical properties. Mechanical 3D metamaterials, with their exceptional behaviour and characteristics, can provide an opportunity to solve the mismatch of mechanical properties between the bone and implant. In this study, a new porous femoral hip meta-implant with graded Poisson’s ratio distribution was introduced and its results were compared to three other femoral hip implants (one solid implant, and two porous meta-implants, one with positive and the other with a negative distribution of Poisson’s ratio) in terms of stress and micromotion distributions. For this aim, first, a well-known auxetic 3D re-entrant structure was studied analytically, and precise closed-form analytical relationships for its elastic modulus and Poisson’s ratio were derived. The results of the analytical solution for mechanical properties of the 3D re-entrant structure presented great improvements in comparison to previous analytical studies on the structure. Moreover, the implementation of the re-entrant structure in the hip implant provided very smooth results for stress and strain distributions in the lattice meta-implants and could solve the stress shielding problem which occurred in the solid implant. The lattice meta-implant based on the graded unit cell distribution presented smoother stress-strain distribution in comparison with the other lattice meta-implants. Moreover, the graded lattice meta-implant gave minimum areas of local stress and local strain concentration at the contact region of the implants with the internal bone surfaces. Among all the cases, the graded meta-implant also gave micromotion levels which are the closest to values reported to be desirable for bone growth (40 µm).

Item Type: Journal article
Publication Title: Materials
Creators: Ghavidelnia, N., Bodaghi, M. and Hedayati, R.
Publisher: MDPI
Date: 29 December 2020
Volume: 14
Number: 1
ISSN: 1996-1944
Rights: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
Divisions: Schools > School of Science and Technology
Record created by: Jonathan Gallacher
Date Added: 11 Jan 2021 14:08
Last Modified: 31 May 2021 15:08
URI: https://irep.ntu.ac.uk/id/eprint/42004

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