Creating Open-celled Solid-state Foams Using Ultrasound

Abstract

Open-celled solid-state foams are expected to have many applications, such as filtration, biochemical sensing, and tissue engineering scaffolding. For bio-related applications, the solid-state foaming process has a unique advantage, i.e., the process does not involve any organic solvent that could leave residues harmful to biological cells. The disadvantage, however, is that solid-state foams are mostly close-celled and do not allow biological cells or fluids to permeate through. This article presents a parametric study on a novel fabrication method to create open-celled solid-state foams using ultrasound. Biodegradable polymer was foamed in a solid-state foaming process. Ultrasound was then applied to break the pore walls. The parameters examined in this study included the pore size, ultrasound power, ultrasound frequency, and water temperature. The inter-pore connectivity was verified using permeability measurements, dye diffusion, and a degradability test. The permeability values were further used to analyze the effects of the experimental parameters. In the analysis a logistic regression model was first used to ensure sample integrity after the ultrasound treatment. A linear regression was then conducted to determine the significance of process variables. It was found that the pore size was the most significant factor affecting the ultrasound effectiveness. The bigger the pores are, the higher the permeability could be obtained with ultrasound. In order to increase the permeability of the ultrasound treated samples, high ultrasound power, high water temperature, and low ultrasound frequency should be used.

Keywords

open-celled solid-state foam ultrasound cavitation ultrasound implosion tissue engineering scaffolds PLA biodegradable foam.

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References

Griffith, L.G. (2002). Emerging Design Principles in Biomaterials and Scaffolds for Tissue Engineering, Annals of the New York Academy of Sciences, 961(1): 83-95.

Mikos, A.G. and Temenoff, J.S. (2000). Formation of Highly Porous Biodegradable Scaffolds for Tissue Engineering, Electronic Journal of Biotechnology , 3: 23-24.

Kumar, V. and Krishna, V.N. (2004). Microcellular Foams, In: Eaves, D. (ed.), Handbook on Polymer Foams, Ch. 9, UK: Rapra.

Rodeheaver, B.A. and Colton, J.S. (2001). Open-celled Microcellular Thermoplastic Foam, Polymer Engineering and Science, 41(3): 380-400.

Dontula, N. , Greener, J. , Fleischer, C.A. , Park, C.B. , Lee, P.C. , Wang, J. and Naguib, H.E. (2005). Manufacturing Process for Open Celled Microcellular Foam, US Patent 6,958,365 B2.

Lee, P.C. , Li, G. , Lee, J.W.S. and Park, C.B. (2006). Extruded Open-cell Foams Using Amorphous Polymers , SPE, ANTEC, Technical Paper #104073: Charlotte, NC.

Wang, X. , Li, W. and Kumar, V. (2006). A Method for Solvent-free Fabrication of Porous Polymer using Solid-state Foaming and Ultrasound for Tissue Engineering Applications , Biomaterials, 27(9): 1924-1929.

Wang, X. , Kumar, V. and Li, W. (2007). Low Density Sub-critical CO2-blown Solid-state PLA Foams, Cellular Polymers, 26(1): 11-35.

Eddy, S.L. (1996). Solid-state PETG Foams, p. ix, 215 leaves, University of Washington, Seattle, WA 98195-2600

10.

del Cerro, M. , Cogen, J. and del Cerro, C. (1980). Stevenel's Blue, An Excellent Stain for Optical Microscopical Study of Plastic Embedded Tissues, Microscopica Acta, 83(2): 117-121.

11.

Chor, M.V. and Li, W. (2007). A Permeability Measurement System for Tissue Engineering Scaffolds, Measurement Science and Technology, 18(1): 208-216.

12.

Agrawal, C.M. , McKinney, J.S. , Lanctot, D. and Athanasiou, K.A. (2000). Effects of Fluid Flow on the In Vitro Degradation Kinetics of Biodegradable Scaffolds for Tissue Engineering, Biomaterials, 21(23): 2443-2452.

13.

Kuehl, R.O. (2000). Design of Experiments: Statistical Principles of Research Design and Analysis, Pacific Grove, CA, USA: Brooks/Cole.

14.

Cam, D. , Hyon, S.H. and Ikada, Y. (1995). Degradation of High Molecular Weight Poly(L-lactide) in Alkaline Medium, Biomaterials, 16(11): 833-843.

15.

Tsuji, H. and Ikada, Y. (1998). Properties and Morphology of Poly(L-lactide). II. Hydrolysis in Alkaline Solution, Journal of Polymer Science, Part A: Polymer Chemistry, 36(1): 59-66.

16.

Tsuji, H. and Tezuka, Y. (2005). Alkaline and Enzymatic Degradation of L-lactide Copolymers, 1: Amorphous-made Films of L-lactide Copolymers with D-lactide , Glycolide, and Epsilon-caprolactone, Macromolecular Bioscience , 5(2): 135-148.

17.

Tsuji, H. , Tezuka, Y. and Yamada, K. (2005). Alkaline and Enzymatic Degradation of L-lactide Copolymers. II. Crystallized Films of Poly(Llactide-co-D-lactide) and Poly(L-lactide) with similar Crystallinities, Journal of Polymer Science, Part B (Polymer Physics), 43(9): 1064-1075.