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Research Papers

Multiscale Design and Multiobjective Optimization of Orthopedic Hip Implants with Functionally Graded Cellular Material

[+] Author and Article Information
Sajad Arabnejad Khanoki

 Mechanical Engineering Department, McGill University, Montreal, Quebec, Canada, H3A 0C3sajad.arabnejadkhanoki@mail.mcgill.ca

Damiano Pasini1

 Mechanical Engineering Department, McGill University, Montreal, Quebec, Canada, H3A 0C3Damiano.pasini@mcgill.ca

1

Corresponding author. Room 372, MacDonald Engineering Building, Mechanical Engineering Department, McGill University, Montreal, Quebec, Canada, H3A 0C3.

J Biomech Eng 134(3), 031004 (Mar 23, 2012) (10 pages) doi:10.1115/1.4006115 History: Received August 30, 2011; Revised February 10, 2012; Posted February 21, 2012; Published March 21, 2012; Online March 23, 2012

Revision surgeries of total hip arthroplasty are often caused by a deficient structural compatibility of the implant. Two main culprits, among others, are bone-implant interface instability and bone resorption. To address these issues, in this paper we propose a novel type of implant, which, in contrast to current hip replacement implants made of either a fully solid or a foam material, consists of a lattice microstructure with nonhomogeneous distribution of material properties. A methodology based on multiscale mechanics and design optimization is introduced to synthesize a graded cellular implant that can minimize concurrently bone resorption and implant interface failure. The procedure is applied to the design of a 2D left implanted femur with optimized gradients of relative density. To assess the manufacturability of the graded cellular microstructure, a proof-of-concept is fabricated by using rapid prototyping. The results from the analysis are used to compare the optimized cellular implant with a fully dense titanium implant and a homogeneous foam implant with a relative density of 50%. The bone resorption and the maximum value of interface stress of the cellular implant are found to be over 70% and 50% less than the titanium implant while being 53% and 65% less than the foam implant.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow chart illustrating the design of a graded cellular hip implant minimizing bone resorption and implant interface failure

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Figure 5

Effective Young’s modulus of 2D square lattice versus relative density. Solution points obtained through homogenization theory are fitted with the least squares method.

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Figure 2

Homogenization concept of a cellular structure

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Figure 3

2D Finite element models of the femur (left) and the prosthesis implanted into the femur (right)

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Figure 4

2D hollow square unit cell for given values of relative density

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Figure 6

Trade-off distributions of relative density for the optimized cellular implant

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Figure 7

Distribution of bone resorption around (a) fully dense titanium implant, (b) cellular implant with uniform relative density of 50%, (c) graded cellular implant (solution B in Fig. 6)

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Figure 8

Distribution of local interface failure f(σ) around (a) fully dense titanium implant, (b) cellular implant with uniform relative density of 50%, (c) graded cellular implant (solution B in Fig. 6)

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Figure 9

Polypropylene proof-of-concept of the optimal graded cellular implant (solution B)

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