Research Papers: Design Automation

Hip Implant Design With Three-Dimensional Porous Architecture of Optimized Graded Density

[+] Author and Article Information
Yingjun Wang

National Engineering
Research Center of Novel Equipment
for Polymer Processing,
The Key Laboratory of Polymer Processing
Engineering of the Ministry of Education,
School of Mechanical
and Automotive Engineering,
South China University of Technology,
Guangzhou 510641, China

Sajad Arabnejad

Department of Mechanical Engineering,
McGill University,
Montreal, QC H3A0C3, Canada

Michael Tanzer

Jo Miller Lab,
Division of Orthopaedic Surgery,
McGill University,
Montreal, QC H3G 1A4, Canada

Damiano Pasini

Department of Mechanical Engineering,
McGill University,
Montreal, QC H3A0C3, Canada
e-mail: damiano.pasini@mcgill.ca

1Corresponding author.

Contributed by the Design Automation Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received March 8, 2018; final manuscript received August 14, 2018; published online September 7, 2018. Assoc. Editor: Andres Tovar.

J. Mech. Des 140(11), 111406 (Sep 07, 2018) (13 pages) Paper No: MD-18-1201; doi: 10.1115/1.4041208 History: Received March 08, 2018; Revised August 14, 2018

Even in a well-functioning total hip replacement, significant peri-implant bone resorption can occur secondary to stress shielding. Stress shielding is caused by an undesired mismatch of elastic modulus between the stiffer implant and the adjacent bone tissue. To address this problem, we present here a microarchitected hip implant that consists of a three-dimensional (3D) graded lattice material with properties that are mechanically biocompatible with those of the femoral bone. Asymptotic homogenization (AH) is used to numerically determine the mechanical and fatigue properties of the implant, and a gradient-free scheme of topology optimization is used to find the optimized relative density distribution of the porous implant under multiple constraints dictated by implant micromotion, pore size, porosity, and minimum manufacturable thickness of the cell elements. Obtained for a 38-year-old patient femur, bone resorption is assessed by the difference in strain energy between the implanted bone and the intact bone in the postoperative conditions. The numerical results suggest that bone loss for the optimized porous implant is only 42% of that of a fully solid implant, here taken as benchmark, and 79% of that of a porous implant with uniform density. The architected hip implant presented in this work shows clinical promise in reducing bone loss while preventing implant micromotion, thereby contributing to reduce the risk of periprosthetic fracture and the probability of revision surgery.

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Fig. 1

Flow chart of the multiscale multiconstraint PTO followed in this work for the 3D design of the hip implant

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Fig. 2

Macrodomain and building block for generating the lattice architecture of the hip implant

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Fig. 3

Effective mechanical properties of tetrahedron-based unit cell; Es is the elastic modulus of the fully solid material

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Fig. 4

Three-dimensional femur model of a 38-year-old male patient: (a) CAD model, (b) physical model of bone apparent density, and (c) FE model with relevant physiological loadings and boundary conditions obtained from in vivo measurements on an instrumented hip [48,59,60]

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Fig. 5

Design domain of the hip implant within the femur

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Fig. 6

Convergence history of the hip stem optimization

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Fig. 7

Relationship between objective function and bone resorption

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Fig. 8

The TO results of the implant: (a) optimized gradients of relative density with zoom (besides) of the implant cross section taken through the plane shown in red and (b) corresponding 3D architecture of the porous stem

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Fig. 9

Bone resorption results for: (a) fully solid implant chosen here as baseline, (b) uniform lattice implant with relative density of 0.5, and (c) graded lattice implant, obtained for volume fraction identical to that of the lattice implant with uniform density (Fig. 8(b))

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Fig. 10

Von Mises stress of the stem with (a) fully solid material, (b) uniform porosity of 0.5, and (c) optimally graded porosity

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Fig. 11

Von Mises stress distribution in the femoral tissue generated by the following implant designs: (a) fully solid, (b) uniform porosity of 0.5, and (c) optimally graded porosity

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Fig. 12

Titanium-based alloy implant with optimized lattice architecture built via SLM

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Fig. 13

B-Rep of an X-shape face with 16 vertices

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Fig. 14

Schematic for automatic generation of a graded lattice structure

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Fig. 15

Optimization of the Messerschmitt–Bölkow–Blohm beam for minimal compliance: (a) design domain and boundary conditions, (b) black-and-white solution obtained with original PTO [37], and (c) gray solution calculate with the density-continuous PTO



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