Biomedical Engineering Reference
In-Depth Information
Figure 5
. Hepatocytes form bile duct-like tubules when appropriate growth factors are
applied (9).
vestigate these behaviors are discussed, starting with the smallest scales and
proceeding to the larger scales.
2.1. Molecular (Submicron) Scale
2.1.1. Cell Signaling
Cells have receptors on their surfaces that interact with various extracellular
molecular signals (see also Part III, chapters 2.2 (by Subramanian and Narang)
and 2.3 (by Goentoro and Shvartsman), this volume). These signals can be flow-
ing in fluid outside the cell (soluble signals) or can be attached to extracellular
matrix or a substrate (insoluble signals). Some of these molecules have been
isolated and identified and are now widely available for researchers to use in
controlling their cell cultures.
A class of signals that is particularly useful to the tissue engineer is the fam-
ily of molecules known as growth factors. This family of factors includes plate-
let-derived growth factor (PDGF), epidermal growth factor (EGF), vascular
endothelial growth factor (VEGF), keratinocyte growth factor (KGF), and many
others. As the name implies, growth factors affect the growth behavior of cells.
The presence of a growth factor may initiate cell proliferation and cell organiza-
tion into structures, and any growth factor will affect different cells in different
ways. The effect of growth factors on a cell type is examined in vitro by cultur-
ing the cell in a dish or on a scaffold and monitoring the cell behavior under
varying amounts of growth factor. Block et al. grew liver cells (hepatocytes) on
a collagen gel matrix, and showed that adding hepatocyte growth factor (HGF)
causes the cells to organize in tubules akin to the bile ducts found in the liver (9)
