34 R. Tran et al.
Better alternatives need to be developed that are less invasive and more
cost effective to provide the needed tissue.
As deﬁned by Langer and Vacanti,
tissue engineering, or regenerative medicine, is “an interdisciplinary ﬁeld that
applies the principles and methods of engineering and life sciences toward the
understanding and development of biological substitutes to restore, maintain, and
improve human tissue functions.” By combining the fundamental principles and
methods from chemistry, engineering, and biological sciences, the major goal of
tissue engineering is to restore damaged or diseased tissue.
The ﬁeld of tissue engineering has progressed for almost 30 years. Due to the
great potential of this ﬁeld, much attention has been attracted to help overcome
major healthcare needs.
Research groups in the ﬁeld have attempted to recreate
a variety of mammalian tissue. For example, ectodermal-, endodermal-, and
mesodermal-derived tissue such as the nerve, cornea, skin, liver, pancreas, carti-
lage, bone, muscle, urethra, bladder, and blood vessels have been investigated.
The foundation of tissue engineering relies on four key elements: cells, scaf-
folds, signals, and bioreactors.
In the general scheme for tissue engineering,
cells are seeded onto a three–dimensional (3D) scaffold, a tissue is cultivated
in vitro, then proper signals are supplemented to the system, and ﬁnally the
construct is implanted into the body as a prosthesis.
The general scheme for the
key elements involved in the tissue engineering paradigm is illustrated in Fig. 3.1.
The cells used in tissue engineering applications can be isolated from either
an autologous, allogenic, or xenogenic source. The cells may be tissue speciﬁc,
stem cells, or progenitor cells. Scaffolds, which provide a substrate for cell growth,
can be composed of either a natural or synthetic material, and fabricated into a
ﬁbrous, foam, hydrogel, or capsule architecture. Signals can be introduced to
enhance cell proliferation, differentiation, and vascularization of the construct.
Bioreactors mimic the conditions inside the body, and provide many beneﬁts
towards a successful design. For example, bioreactors allow for an increase in
Figure 3.1. The key elements involved in the classic tissue engineering paradigm. For
color reference, see page 255.
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