Research Papers

Selective Ultrasonic Foaming of Polymer for Biomedical Applications

[+] Author and Article Information
Hai Wang, Wei Li

Department of Mechanical Engineering, University of Washington, Seattle, WA 98195-2600

J. Manuf. Sci. Eng 130(2), 021004 (Mar 07, 2008) (9 pages) doi:10.1115/1.2823078 History: Received April 27, 2007; Revised November 05, 2007; Published March 07, 2008

Biocompatible polymeric material with well-defined, interconnected porous structure plays an important role in many biomedical applications, such as tissue engineering, controlled drug release, biochemical sensing, and 3D cell culture for drug discovery. In this study, a novel fabrication process for porous polymer is developed using high intensity focused ultrasound. This acoustic method is solvent-free and capable of creating interconnected porous structures with varying topographical features at designed locations. An experimental study on the selective ultrasonic foaming technique is presented in this paper. We investigated the effects of major process variables, including ultrasound power, scanning speed, and gas concentration. Both pore size and interconnectivity of the created porous structures were examined. It was found that the pore size could be controlled with the scanning speed of the ultrasound insonation and that interconnected porous structures could be obtained using a partial saturation procedure. A concentration-dependent gas diffusion model was developed to predict the gas concentration profiles for partially saturated samples. A cell culture study was conducted to examine cell growth behavior in the fabricated porous structures.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

The setup of the selective ultrasonic foaming process

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Figure 2

A schematic of the sound field of a HIFU transducer

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Figure 3

A PMMA sample with thermocouples embedded in a cross pattern and the numbering of the thermocouples

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Figure 4

PMMA-CO2 saturation curves with different saturation pressures

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Figure 5

Temperature measurements in PMMA with insonation parameters: (a) 13s, 2w, focal point on Thermocouple 3; (b) 61s, 1w, focal point on Thermocouple 1; and (c) 104s, 1w, focal point between Thermocouples 4 and 5.

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Figure 6

A typical PMMA specimen foamed using the selective ultrasonic foaming process.

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Figure 7

Effects of ultrasound scanning speed: (a) 2.4in.∕min, (b) 1.8in.∕min, (c) 1.2in.∕min, and (d) 0.6in.∕min. Scale bar is 100μm.

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Figure 8

Effects of ultrasound power: (a) 8W, (b) 10W, (c) 15W, and (d) 20W. Scale bar is 100μm.

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Figure 9

The SEM image of an open-celled PMMA specimen (scale bar 200μm)

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Figure 10

Two different open-celled porous structures on a single PMMA sample foamed using the selective ultrasonic foaming process. Nominal diameters: (a) 88μm and (b) 182μm. The scale bars are 200μm.

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Figure 11

A schematic of the gas diffusion model

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Figure 12

SEM images of foamed specimens with corresponding gas concentration profiles overlaid on the images. Both samples were saturated at 2MPa until the overall gas concentration reached 4%. The desorption times were different: (a) 0.5h, and (b) 6h. The scale bars are 200μm.

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Figure 13

Live/dead staining of SMCs on porous PMMA samples to determine cell viability: (a) pore size 200μm and (b) pore size 70μm




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