Biomedical Engineering Reference
In-Depth Information
Figure 20 . Silicon mold for a microfabricated capillary bed (left) and biodegradable
vascular network (right) (10).
tissue and seeded with cells. Such a design can be implanted, so that when the
polymer degrades the remaining cells form a completely natural tissue. Such
devices have demonstrated organ function (49).
The design of a microfabricated network comes from numerical tools de-
veloped for the task (36,77). The flow of blood through a microfluidic device is
simulated analogously to the calculation of currents in a resistor network. Each
blood vessel has a fluidic resistance dependent on the vessel geometry and vis-
cosity of the fluid, and the pressure drop from one end of the vessel to the other
is related to the flow rate through the vessel by
P = QR ,
[5]
where P is the pressure drop, Q is the flow rate, and R is the fluid resistance.
The flow rates and pressures throughout the network are interdependent, so the
equations for all the vessels are solved simultaneously as a matrix equation.
Thus, if the geometry of a network is known, the flow behavior can be calcu-
lated. The geometry can be modified iteratively to create a network with the
desired flow properties, or the system can be solved in reverse to determine the
geometry from the flow conditions. If physiological flow conditions are speci-
fied, the resulting design will be a microfluidic network with physiological flow
characteristics (see also this volume, Part IV, chapter 1, by Meinhart and
Wereley).
The other approach is to create an experimental setting where the organ can
self-assemble. In this approach, cell growth is controlled in a matrix material so
that the cells form vasculature and organ features instead of designing and mold-
ing the features. Currently, there is much research aimed at understanding, con-
trolling, and mimicking the natural process of vasculature formation, known as
angiogenesis.
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