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Research Papers

Porogen Templating Processes: An Overview

[+] Author and Article Information
Yifeng Hong

School of Materials Science and Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Jack G. Zhou

Department of Mechanical
Engineering and Mechanics,
Drexel University,
Philadelphia, PA 19104

Donggang Yao

School of Materials Science and Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: yao@gatech.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received August 6, 2013; final manuscript received February 14, 2014; published online March 26, 2014. Assoc. Editor: Wei Li.

J. Manuf. Sci. Eng 136(3), 031013 (Mar 26, 2014) (17 pages) Paper No: MANU-13-1304; doi: 10.1115/1.4026899 History: Received August 06, 2013; Revised February 14, 2014

Porous materials with well-defined pore shapes, sizes and distributions are highly desired in many emerging applications, particularly for biomedical materials and devices. However, conventional methods for processing porous materials only demonstrated limited capability in morphological control. One promising solution is the porogen templating process, where a structured porogen pattern is created first and subsequently used as a template or mold for generation of the desired porous material. Particularly, with solid freeform fabrication, porogen templates having complex internal structures can be additively fabricated, and they can then be used as molds for molding of porous materials and devices. This article attempts to offer a constructive overview on the state of the art of porogen patterning and inverse molding, with the goal of explaining the working mechanisms and providing unbiased accounts of the pros and cons of existing techniques and process variants. The article further intends to provide a fundamental understanding of the constituent elements and corresponding building blocks in porogen templating processes. An increased understanding of these elements will facilitate the development of more capable new processes.

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Figures

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Fig. 4

Diagram of the main processes in the bone scaffold and tissue manufacturing system [31]

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Fig. 3

An example porogen design with a complex layout of trusses and beams corresponding to a complex layout of channels in the resulting porous replicate

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Fig. 2

A Venn diagram showing the relation of indirect SFF, particle assembly and templating, porogen templating, and lost-core molding and casting

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Fig. 1

A simplified illustration of the porogen templating process involving three sequential stages: (a) preparing a porogen template; (b) molding or casting of the desired polymeric material; and (c) removing the porogen template [34]

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Fig. 5

Illustration of a microsphere-templating process: wax microsphere template sintering (a), polymer casting (b), wax microsphere template removal (c), and resulting porous structure (d) [22]

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Fig. 6

Schematics for the two paths to generate gradient porogen template: (a) the first path to mix porogens with molding materials and then form a gradient (multiple tape-casting technique is shown) and (b) the second path to form gradient porogen template before casting materials

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Fig. 7

Different molding and casting processes by (a) injection; (b) gravity casting; (c) vacuum infusion; (d) capillary wetting; and (e) centrifuging casting

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Fig. 8

A flow chart illustrates scaffold fabrication using a hybrid method combining indirect solid freeform with particle assembly [109]

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