Bioreactors; Cell Culture Techniques/instrumentation; Cell Differentiation; Embryonic Stem Cells/cytology; Lactic Acid/pharmacology; Liver/cytology; Polymers/pharmacology; Weightlessness; Albumins/metabolism; Animals; Cell Differentiation/drug effects; Cell Differentiation/genetics; Cell Proliferation/drug effects; Cell Shape/drug effects; Cytochrome P-450 Enzyme System/metabolism; Embryoid Bodies/cytology; Embryoid Bodies/drug effects; Embryoid Bodies/transplantation; Embryoid Bodies/ultrastructure; Embryonic Stem Cells/drug effects; Embryonic Stem Cells/ultrastructure; Flow Cytometry; Fluorescent Antibody Technique; Gene Expression Regulation/drug effects; Lipoproteins, LDL/metabolism; Liver/metabolism; Mice; Mice, SCID; Organ Specificity/drug effects; Organ Specificity/genetics; Polyesters; Rotation; Tissue Scaffolds/chemistry