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Research Papers

Modeling of the Flow Rate in the Dispensing-Based Process for Fabricating Tissue Scaffolds

[+] Author and Article Information
X. B. Chen1

Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canadaxbc719@mail.usask.ca

M. G. Li, H. Ke

Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canada

1

Corresponding author.

J. Manuf. Sci. Eng 130(2), 021003 (Mar 07, 2008) (7 pages) doi:10.1115/1.2789725 History: Received December 29, 2006; Revised August 20, 2007; Published March 07, 2008

Made from biomaterials, tissue scaffolds are three-dimensional (3D) constructs with highly interconnected pore networks for facilitating cell growth and flow transport of nutrients and metabolic waste. To fabricate the scaffolds with complex structures, dispensing-based rapid prototyping technique has been employed recently. In such a fabrication process, the flow rate of biomaterial dispensed is of importance since it directly contributes to the pore size and porosity of the scaffold fabricated. However, the modeling of the flow rate has proven to be a challenging task due to its complexity. This paper presents the development of a model for the flow rate in the scaffold fabrication process based on the fundamentals of fluid mechanics. To verify the effectiveness of the developed model, experiments were carried out, in which the chitosan solution (2% w/v) in acetic acid was used for dispensing under different applied pressures (50kPa, 100kPa, 150kPa, 200kPa, and 250kPa) and needle heater temperatures (25°C, 35°C, 50°C, and 65°C). The measured flow rates were used to identify the flow behavior of the solution and were compared to the predictions from the developed model to illustrate the model effectiveness. Based on the developed model, simulations were carried out to identify the effects of the needle size and the flow behavior on the flow rate in the scaffold fabrication process. The developed model was also applied to determine the dispensing conditions for fabricating 3D scaffolds from a 50% chitosan-hydroxyapatite colloidal gel. As an example, a scaffold fabricated with a well-controlled internal structure of diameters of 610±43μm and pore sizes of 850±75μm in the horizontal plane and of 430±50μm in the vertical direction is presented in this paper to illustrate the promise of the developed model as applied to the 3D scaffold fabrication.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow curves of the chitosan solution at different temperatures

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Figure 2

Schematic of the dispensing system for scaffold fabrication

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Figure 3

Pneumatic dispenser: (a) close-up view and (b) schematic

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Figure 4

Dispenser and the pressures of interest

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Figure 5

Effect of the fluid surface tension

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Figure 6

Flow rate versus applied air pressure at the needle heat temperatures of (a) 25°C, (b) 35°C, (c) 50°C, and (d) 65°C

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Figure 7

Simulated flow rate versus applied air pressure: (a) dispensing biomaterials with different power law indices and (b) using different needle diameters

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Figure 8

3D scaffold fabricated (a) top view and (a) cross section

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Figure 9

Strands formed by using different speeds

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Figure 10

Scaffold fabricated by using an inappropriate speed

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