Reverse fabrication of porous materials

Details Reverse fabrication of porous materials Reverse fabrication of porous materials

2001-05-11

2004-01-06

Kuhns, Allan R. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Pore forming in situ

By treating occluded solids

C029S527100, C264S219000, C264S317000

Reexamination Certificate

active

06673285

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to methods for fabricating porous materials, and more particularly to such methods using a reverse fabrication technique, utilizing a three-dimensional negative replica formed from a porogen material. The resulting variety of inventive porous materials may be used for many different applications such as tissue engineering scaffolds, cell culture matrices, controlled release matrices, wound dressings, separation membranes, column fillers of chromatography, filters, packaging and insulating materials, and so forth.
Engineering tissues and organs with mammalian cells and a scaffolding material is a new approach compared to the use of harvested tissues and organs. See Langer, R. S. and J. P. Vacanti, “Tissue engineering: the challenges ahead,”
Scientific American
280(4), 86 (1999). In the tissue engineering approach, the scaffold plays a pivotal role in cell seeding, proliferation, and new tissue formation in three dimensions. See Langer, R. and J. Vacanti, “Tissue engineering,”
Science
260(5110), 920-926 (1993); Hubbell, J. A., “Biomaterials in Tissue Engineering,”
Bio/Technology
13, 565 (1995); and Saltzman, W. M., “Cell Interactions with Polymers,”
Principles of Tissue Engineering
, R. Lanza, R. Langer and W. Chick, Editors, (1997) Academic Press, R. G. Landes Company, Austin, Tex., 225. Biodegradable polymers have been attractive candidates for scaffolding materials because they degrade as the new tissues are formed, eventually leaving nothing foreign to the body. See Ma, P. X. and R. Langer, “Degradation, structure and properties of fibrous nonwoven poly(glycolic acid) scaffolds for tissue engineering,”
Polymers in Medicine and Pharmacy
, A. G. Mikos, K. W. Leong, M. L. Radomsky, J. A. Tamada and M. J. Yaszemski, Editors, (1995) MRS, Pittsburgh, 99-104. A few techniques such as salt-leaching (see Mikos, A. G., A. J. Thorsen, L. A. Czerwonka, Y. Bao, R. Langer, D. N. Winslow and J. P. Vacanti, “Preparation and characterization of poly(l-lactic acid) foams,”
Polymer
35(5), 1068-1077 (1994); and Ma, P. X. and R. Langer, “Fabrication of biodegradable polymer foams for cell transplantation and tissue engineering,”
Tissue Engineering Methods and Protocols
, M. Yarmush and J. Morgan, Editors, (1998) Humana Press Inc., Totowa, N.J.), fibrous fabric processing, 3-D printing (see Park, A., B. Wu and L. G. Griffith, “Integration of surface modification and 3D fabrication techniques to prepare patterned poly(L-lactide) substrates allowing regionally selective cell adhesion,”
Journal of Biomaterials Science Polymer Edition
9(2), 89-110 (1998)), and phase-separation (see Zhang, R. and P. X. Ma, “Poly (alpha-hydroxy acids)/hydroxyapatite porous composites for bone tissue engineering: 1. Preparation and morphology,”
Journal of Biomedical Materials Research
44(4), 446-455 (1999); Zhang, R. and P. X. Ma, “Porous poly(L-lactic acid)/apatite composites created by biomimetic process,” Journal of Biomedical Materials Research 45(4), 285-293 (1999); Ma, P. X. and R. Zhang, “Synthetic nano-scale fibrous extracellular matrix,”
Journal of Biomedical Materials Research
46(1):60-72 (May 3, 1999); and Lo, H., S. Kadiyala, S. E. Guggino and K. W. Leong, “Poly(L-lactic acid) foams with cell seeding and controlled-release capacity,”
J Biomed Mater Res
30(4), 475-484 (1996)) have been developed to generate highly porous polymer scaffolds for tissue engineering.
These scaffolds have shown great promise in the research of engineering a variety of tissues. See, for example, Vacanti, C. A. and L. J. Bonassar, “An overview of tissue engineered bone,”
Clinical Orthopaedics
&
Related Research
(367 Suppl), S375 (1999); Freed, L. E., R. Langer, I. Martin, N. R. Pellis and G. Vunjak-Novakovic, “Tissue engineering of cartilage in space,”
Proceedings of the National Academy of Sciences of the United States of America
94(25), 13885-13890 (1997); Ma, P. X., B. Schloo, D. Mooney and R. Langer, “Development of biomechanical properties and morphogenesis of in vitro tissue engineered cartilage,”
J Biomed Mater Res
29(12), 1587-1595 (1995); Ma, P. X. and R. Langer, “Morphology and mechanical function of long-term in vitro engineered cartilage,”
Journal of Biomedical Materials Research
44(2), 217-221 (1999); Cao, Y., J. Vacanti, X. Ma, K. Paige, J. Upton, Z. Chowanski, B. Schloo, R. Langer and C. Vacanti, “Generation of neo-tendon using synthetic polymers seeded with tenocytes,”
Transplant Proc
26(6), 3390-3392 (1994); Ibarra, C., C. Jannetta, C. A. Vacanti, Y. Cao, T. H. Kim, J. Upton and J. P. Vacanti, “Tissue engineered meniscus: a potential new alternative to allogeneic meniscus transplantation,”
Transplantation Proceedings
29(1-2), 986 (1997); Cusick, R. A., H. Lee, K. Sano, J. M. Pollok, H. Utsunomiya, P. X. Ma, R. Langer and J. P. Vacanti, “The effect of donor and recipient age on engraftment of tissue engineered liver,”
Journal of Pediatric Surgery
32(2), 357 (1997); Shinoka, T., P. X. Ma, D. Shum-Tim, C. K. Breuer, R. A. Cusick, G. Zund, R. Langer, J. P. Vacanti and J. E. Mayer, Jr., “Tissue-engineered heart valves, Autologous valve leaflet replacement study in a lamb model,”
Circulation
94(9 Suppl), 11-164-168 (1996); Shinoka, T., D. Shum-Tim, P. X. Ma, R. E. Tanel, N. Isogai, R. Langer, J. P. Vacanti and J. E. Mayer, Jr., “Creation of viable pulmonary artery autografts through tissue engineering,”
Journal of Thoracic & Cardiovascular Surgery
115(3), 536 (1998); Niklason, L. E., J. Gao, W. M. Abbott, K. K. Hirschi, S. Houser, R. Marini and R. Langer, “Functional arteries grown in vitro,”
Science
284(5413), 489-493 (1999); Cao, Y., J. P. Vacanti, K. T. Paige, J. Upton and C. A. Vacanti, “Transplantation of chondrocytes utilizing a polymer-cell construct to produce tissue-engineered cartilage in the shape of a human ear,”
Plastic
&
Reconstructive Surgery
100(2), 297 (1997); and my co-pending patent application entitled, “Porous Composite Materials,” U.S. Ser. No. 09/292,896, filed Apr. 27, 1999.
However, to engineer clinically useful tissues and organs is still a challenge. The understanding of the principles of scaffolding is far from satisfactory, and “ideal” scaffolds are yet to be developed.
Pore size, porosity, and surface area (surface-to-volume ratio) are widely recognized as important parameters for a scaffold for tissue engineering. See Ishaug-Riley S. L., G. M. Crane-Kruger, M. J. Yaszemski and A. G. Mikos, “Three-dimensional culture of rat calvarial osteoblasts in porous biodegradable polymers,”
Biomaterials
19(15), 1405 (1998). Other architectural features such as pore shape, pore wall morphology, and interconnectivity between pores of the scaffolding materials are also suggested to be important for cell seeding, migration, growth, mass transport, gene expression and new tissue formation in three dimensions.
In the body, tissues are organized into three-dimensional structures as functional organs and organ systems. Each tissue or organ has its specific characteristic architecture depending on its biological function. This architecture is also believed to provide appropriate channels for mass transport and spatial cellular organization. Mass transport includes signaling molecules, nutritional supplies, and metabolic waste removal. Spatial cellular organization determines cell—cell and cell-matrix interactions, and is critical to the normal tissue and organ function. To engineer a tissue or organ with a specific function, a matrix material (natural or synthetic) plays a critical role in allowing for the appropriate cell distribution and in guiding the tissue regeneration in three-dimensions. Therefore, to develop a scaffold for tissue engineering, the architectural design concerning the spatial cellular distribution, mass transport conditions, and tissue function is very important.
A few methods have been developed to produce porous scaffolds for tissue engineering. See Langer R., “Selected advances in drug delivery and tissue engineering,”
Journal of Controlled Release,
62(1-2):7-11 (1999); Ma

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