endothelial cells on collagen type I

[Dana L.]

Hello everybody,

I have been trying to grow aortic bovine endothelial cells on collagen
type I originated in rat¡¯s tails.
When the layer of collagen is thin (about a millimeter) the cells
proliferate like on a culture dish.  As the thickness of the collagen
increase, fewer cells last, and when the thickness of the collagen is
about 4 millimeters, non survive.

What could be the reason for this phenomena?

Thanx in advance