The proposed work addresses several long-term goals. The most general is the development of a new class of biomaterials which will interact specifically with differentiated epithelial cell types but which are inert toward other cells, notably those involved in fibrotic tissue response. Such materials would have wide application in tissue and organ regeneration. The proposed work focusses on the development of such a material for one specific cell type, liver, as a paradigm. Hepatospecific materials are particularly interesting because they might he extremely useful in vitro as well as in vivo--in vivo for tissue regeneration, and in vitro as a substrate for long-term maintenance of differentiated hepatocytes. Such a substrate could form the basis of creating large-scale in vitro toxicology assays to replace animal testing of pharmaceuticals, and may also contribute to the fundamental understanding of hepatic cell biology. The unique hepatospecific material to be developed will be characterized first as a cell culture substrate. The other major application of such a material addressed in this work is the development of a method for liver cell transplantation for treatment of liver disease. A key factor in the success of cell transplantation is development of appropriate materials for the support matrix. Materials which have been investigated to date are known to induce chronic inflammation and fibrosis, and this inflammatory reaction creates a hostile environment which may severely compromise the survival of the transplanted cells; long-term cell survival and function have not been achieved in previous studies of hepatocyte transplantation on polymer supports. Polyethylene oxide (PEO) hydrogels, which demonstrate very low protein adsorption and cell adhesion, have previously been developed for other in vivo therapeutic applications. These materials have not been applied to cell transplantation because an implicit requirement of the cell transplantation substrate is that the cells to be transplanted adhere to it. It is proposed to covalently modify crosslinked PEO gels with carbohydrate groups which interact specifically with hepatocytes via the unique hepatic asialoglycoprotein receptor. Such a material has the potential to provide not only for initial cell adhesion, but to act as a template to guide the growth of hepatocytes in vivo. A panel of materials in which the type and concentration of carbohydrate adhesion moieties is systematically varied will be characterized in vitro with respect to adhesion and spreading of hepatocytes, macrophages and fibroblasts. Select materials to which hepatocytes adhere will be evaluated as potential cell culture substrates by quantifying the growth and differentiated function of cells maintained on the substrates for 1-2 weeks. Materials which are good substrates for hepatocyte adhesion but poor substrates for fibroblast and macrophage adhesion will be further tested in vivo as vehicles for hepatocyte transplantation. Cells attached to the substrates will be transplanted between inbred rats and cell survival will be quantified over a six month period.
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