Vasculogenesis and angiogenesis are two different mechanisms for blood
vessel formation. Angiogenesis occurs when new vessels sprout from
pre-existing vasculature in response to external chemical stimuli.
Vasculogenesis occurs via the reorganization of randomly distributed
cells into a blood vessel network. Experimental models
of vasculogenesis have suggested that the cells exert traction forces
onto the extracellular matrix and that these forces may play
an important role in the network forming process.
In order to study the role of the mechanical and chemical forces
in both of these stages of blood vessel formation, we present a
mathematical model which assumes that (i) cells exert traction forces
onto the extracellular matrix, (ii) the matrix behaves as a linear
viscoelastic material, (iii) the cells move along gradients of
exogenously supplied chemical stimuli (chemotaxis)
and (iv) these stimuli diffuse or are uptaken by the cells.
We study the equations numerically, present an
appropriate finite difference scheme and simulate the formation of
vascular networks in a plane. Our results compare very well with
experimental observations and suggest that spontaneous formation of
networks can be explained via a purely mechanical interaction between
cells and the extracellular matrix. We find that chemotaxis alone is not
a sufficient force to stimulate formation of pattern. Moreover, during
vessel sprouting, we find that mechanical forces can help in the formation
of well defined vascular structures.