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Research Papers

Design Optimization of Scaffold Microstructures Using Wall Shear Stress Criterion Towards Regulated Flow-Induced Erosion

[+] Author and Article Information
Yuhang Chen, Shiwei Zhou, Joseph Cadman, Wei Li

School of Aerospace, Mechanical and Mechatronic Engineering,  The University of Sydney, Sydney, NSW 2006, Australia

Michiel Schellekens

Department of Mechanical Engineering,  Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

Richard Appleyard

School of Medicine,  Macquarie University, NSW 2109, Australia

Qing Li1

Member of ASME, School of Aerospace, Mechanical and Mechatronic Engineering,  The University of Sydney, Sydney, NSW 2006, AustraliaQing.Li@Sydney.edu.au

1

Corresponding author.

J Biomech Eng 133(8), 081008 (Sep 19, 2011) (10 pages) doi:10.1115/1.4004918 History: Received April 19, 2011; Revised August 18, 2011; Posted August 22, 2011; Published September 19, 2011

Tissue scaffolds aim to provide a cell-friendly biomechanical environment for facilitating cell growth. Existing studies have shown significant demands for generating a certain level of wall shear stress (WSS) on scaffold microstructural surfaces for promoting cellular response and attachment efficacy. Recently, its role in shear-induced erosion of polymer scaffold has also drawn increasing attention. This paper proposes a bi-directional evolutionary structural optimization (BESO) approach for design of scaffold microstructure in terms of the WSS uniformity criterion, by downgrading highly-stressed solid elements into fluidic elements and/or upgrading lowly-stressed fluidic elements into solid elements. In addition to this, a computational model is presented to simulate shear-induced erosion process. The effective stiffness and permeability of initial and optimized scaffold microstructures are characterized by the finite element based homogenization technique to quantify the variations of mechanical properties of scaffold during erosion. The illustrative examples show that a uniform WSS is achieved within the optimized scaffold microstructures, and their architectural and biomechanical features are maintained for a longer lifetime during shear-induced erosion process. This study provides a mathematical means to the design optimization of cellular biomaterials in terms of the WSS criterion towards controllable shear-induced erosion.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow chart of BESO topology optimization and shear-induced erosion algorithms

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Figure 2

Benchmark design example of a 90 deg turn pipe. (a) Design problem; (b) Optimal fluid structure; (c) Evolutionary histories of objective function and volume fraction of solid phase; and (d) WSS histogram after the optimization.

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Figure 3

Design optimization of scaffold micro-architecture under tri-directional flow with the initial design of four isolated vertical bars. (a) Convergence history and topological snapshots during optimization; and (b) Shear-induced erosion histories of initial and optimized designs; (c)–(d) Effective stiffness and permeability components of the initial and optimized scaffold designs.

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Figure 4

Topological evolutions during design optimization under mono-directional flow (k denotes the iteration number). Initial design: four isolated vertical bars.

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Figure 5

Design optimization under mono-directional flow. Initial design: four isolated vertical bars. (a) Wall shear stress histogram and (b) erosion processes of the initial and optimal structures.

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Figure 6

Design optimization of scaffold micro-architecture under mono-directional flow. Initial design: inter-connected bars. (a) Convergence history and topological snapshots during optimization and (b) WSS histograms of initial and optimized designs.

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Figure 7

Shear-induced erosion of optimized design under mono-directional flow. (a) Evolutions of scaffold volume loss in the initial and optimized designs and corresponding RVE structures. (b)–(c) Effective stiffness and permeability in the x direction of both initial and optimized scaffold designs. Since the lateral surfaces of optimized structure are weakened under mono-directional shear flow, only the component in the x direction is presented.

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Figure 8

Two representative optimal scaffold macro-structures (4 × 4 × 4 RVEs) designed by the WSS uniformity criterion. (a) Design under tri-directional flow as obtained from Fig. 3; (b) under mono-directional flow as obtained from Fig. 6.

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