Biomedical Engineering Reference
In-Depth Information
Figure 19
. Schematic of liver assist device, animal experiment (67).
The success of these devices is possible only when the nutrient transport,
cell attachment to scaffold, co-culture, and cell response to flow are controlled
(64,65,67,75).
3.
CONTINUING EFFORTS IN TISSUE ENGINEERING
Many groups continue to show success with engineering of simpler tissues
such as skin, blood vessel walls, cartilage, and heart valves. These tissues are
thin enough that they do not require vascularization, since diffusion can carry
any necessary nutrients throughout the thickness of the tissue. Larger organs,
though, are much thicker and require a vascular network to keep the cells alive
and carry any products of the organ's activity. These systems are truly complex,
and encompass the entire range of phenomena discussed here.
Two main approaches have been conceived for the fabrication of vascular-
ized tissues. The first approach is to construct the entire vasculature. This is
made possible by advances in micromachining (38) and the use of photolitho-
graphy to create high-resolution patterns on a silicon wafer (21). Recently,
methods have been developed for transferring the pattern from silicon to softer
materials, such as polymers suitable for tissue engineering (78). Borenstein et al.
have demonstrated the ability to construct complete blood vessel networks using
these "soft lithography" techniques.
These vascular devices are fabricated by first creating the vascular pattern
in a silicon wafer (Figure 20). Then polymer devices are replica-molded from
the silicon master. The polymer devices are stacked to create three-dimensional
