Controlled Release of Fibroblast Growth Factor: Activity in Cell Culture
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CONTROLLED RELEASE OF FIBROBLAST GROWTH FACTOR: ACTIVITY IN CELL CULTURE Matthew A. Nugent*#, Oliver S. Chen#, and Elazer R. Edelman*§ *
Harvard-M.I.T., Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139
#
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
§
Cardiovascular Division, Department of Internal Medicine, Brigham and Woman's Hospital and Harvard Medical School, Boston, MA 02115
ABSTRACT Basic fibroblast growth factor is a multi-potent cell regulatory factor that stimulates proliferation and angiogenesis. Controlled studies of basic fibroblast growth factor in animals have been hindered by the instability of this protein. In addition, many cells appear to require the continuous addition of basic fibroblast growth factor for optimal growth and function in culture. A system for the sustained delivery of active basic fibroblast growth factor might provide both a means to conduct log-term studies on activity and provide a practical alternative to multiple growth factor additions to cell cultures. Basic fibroblast growth factor was incorporated into standard polymer matrices, but the released growth factor had lost over 99% of its bioactivity. Loss of basic fibroblast growth factor activity was found to result from both physical inactivation and adsorption of the protein to surfaces. These problems were avoided by incorporating the growth factor into calcium cross-linked alginate microspheres containing heparinsepharose beads. Basic fibroblast growth factor was incorporated into these microspheres with 71% efficiency and active growth factor was released with predictable kinetics for up to 7 weeks. Release from these microspheres was controlled by the amount of heparin within the device and could be manipulated by simply altering the heparin content during fabrication. Alginate/heparin-sepharose microspheres were placed into growing cultures of bovine aortic endothelial cells and no cytotoxic effects were observed. Furthermore, microspheres containing growth factor provided long-term stimulation of cell proliferation and maintenance of endothelial cell morphology.
INTRODUCTION Growth factors are an important class of proteins that regulate many aspects of mammalian cell function such as growth, differentiation and metabolism [1]. Most growth factors are produced by a variety of cell types and act on a wide spectrum of tissues in minute quantities (nanogram to microgram). As a result of the scope of activity of growth factors, many potential applications for these compounds are being proposed. In a sense most human diseases have a Mat. Res. Soc. Symp. Proc. Vol. 252. t1992 Materials Research Society
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component that involves an alteration of growth control. Thus, much of current biomedical research has focussed on understanding the role of abnormal cell growth in disease, and in defining mediators (growth factors) of cell proliferation in different disease states. Atherosclerosis, cancer, peptic ulcers, no
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