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Research Papers: Design Automation

Design of Hierarchical Three-Dimensional Printed Scaffolds Considering Mechanical and Biological Factors for Bone Tissue Engineering

[+] Author and Article Information
Paul F. Egan

Department of Health Sciences and Technology,
ETH Zurich,
Honggerbergring 64,
Zurich 8093, Switzerland
e-mail: pegan@ethz.ch

Stephen J. Ferguson

Department of Health Sciences and Technology,
Institute for Biomechanics,
ETH Zurich,
Honggerbergring 64,
Zurich 8093, Switzerland
e-mail: sferguson@ethz.ch

Kristina Shea

Department of Mechanical and Process
Engineering,
ETH Zurich,
Zurich 8092, Switzerland
e-mail: kshea@ethz.ch

1Corresponding author.

Contributed by the Design Automation Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received December 3, 2016; final manuscript received March 18, 2017; published online April 24, 2017. Assoc. Editor: Katja Holtta-Otto.

J. Mech. Des 139(6), 061401 (Apr 24, 2017) (9 pages) Paper No: MD-16-1807; doi: 10.1115/1.4036396 History: Received December 03, 2016; Revised March 18, 2017

Computational approaches have great potential for aiding clinical product development by finding promising candidate designs prior to expensive testing and clinical trials. Here, an approach for designing multilevel bone tissue scaffolds that provide structural support during tissue regeneration is developed by considering mechanical and biological perspectives. Three key scaffold design properties are considered: (1) porosity, which influences potential tissue growth volume and nutrient transport, (2) surface area, which influences biodegradable scaffold dissolution rate and initial cell attachment, and (3) elastic modulus, which influences scaffold deformation under load and, therefore, tissue stimulation. Four scaffold topology types are generated by patterning beam or truss-based unit cells continuously or hierarchically and tuning the element diameter, unit cell length, and number of unit cells. Parametric comparisons suggest that structures with truss-based scaffolds have higher surface areas but lower elastic moduli for a given porosity in comparison to beam-based scaffolds. Hierarchical scaffolds possess a large central pore that increases porosity but lowers elastic moduli and surface area. Scaffold samples of all topology types are 3D printed with dimensions suitable for scientific testing. A hierarchical scaffold is fabricated with dimensions and properties relevant for a spinal interbody fusion cage with a maximized surface-volume ratio, which illustrates a potentially high performing design configured for mechanical and biological factors. These findings demonstrate the merit in using multidisciplinary and computational approaches as a foundation of tissue scaffold development for regenerative medicine.

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Figures

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Fig. 1

Design approach for testing scaffold samples rescaled for interbody fusion cage products

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Fig. 2

Multilevel scaffold design

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Fig. 3

Scaffold topology types

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Fig. 4

Planar schematic of hierarchical truss with indicated element diameter ø, unit cell length Lc, number of unit cells Nc, and lengths L1, L2, L3, and L4

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Fig. 6

Designs for each topology type generated by independently sweeping design parameters (a) number of cells Nc, (b) unit cell length Lc, and (c) element diameter ø for (A1, B1, C1) porosity, (A2, B2, C2) surface–volume ratio, and (A3, B3, C3) relative elastic modulus

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Fig. 7

Designs for each topology type generated by sweeping element diameter ø from 200 μm to 1400 μm with pore size p=1 mm and scaffold length Ls≤1.5 cm for (a) surface–volume ratio and (b) relative elastic modulus

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Fig. 5

Continuous beam designs with parameters normalized to Nc=12, Lc=2.0 mm, and ø=800 μm for (a) porosity, (b) surface–volume ratio, and (c) relative elastic modulus

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Fig. 8

(a) Data from Fig. 7(a) replotted for element diameter ø. A hierarchical truss with number of cells Nc=9, cell length Lc=1.5 mm, and element diameter ø=500 μm is selected and (b) patterned with dimensions relevant for an interbody cage; note that adjacent second-order unit cells share first-order unit cells when patterned to form a tailored structure.

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