Biomedical Engineering Reference
In-Depth Information
treatment strategies to minimize scarring. It is fascinating to note that fetal wounds
are healed without scar formation. Elucidation of the molecular mechanisms and
physical and chemical cues that are responsible for scarless fetal wound healing
would lead to ideal tissue repair, but currently remains unknown (Colwell et al.
2005
) . Identifi cation of such mechanisms and cues would undoubtedly be useful for
attempts to engineer a skin-equivalent tissue replacement construct. Indeed, one of
the most successful tissue-engineering applications up to date has been the treat-
ment of skin wound that incorporates keratinocytes and fi broblasts seeded in both
natural and synthetic ECM. Advances in tissue engineering of tissue types other
than skin are also rapidly progressing. Some recent developments of tissue engi-
neering in creating ECM for tissue restoration and other biomedical applications are
described in the following section. Finally, electrotherapy for wound healing has
been applied over the past two decades. Although the molecular mechanisms that
mediate electrically stimulated wound healing are yet to be fully elucidated, a recent
review suggests that several cellular events are induced and coordinated by electri-
cal stimulation to promote cell adhesion and migration that reorganizes ECM struc-
tures [see Cho (
2002
) ) for review].
4
Role of ECM in Tissue Engineering
Based on the important and critical role of ECM to infl uence cellular and molecular
responses, development of extracellular environment has become a key task for tis-
sue engineering, regenerative medicine, and other biomedical and pharmaceutical
applications. Successful tissue engineering requires appropriate integration of at
least three critical components: cells; natural or synthetic scaffold that can serve as
a temporary ECM; and chemical and physical elements, such as growth factors and
topographical features that best mimic the extracellular environment in the natural
ECM. Scaffold must be engineered in a way that is conducive to cell proliferation,
differentiation, and eventual integration with the surrounding tissue. Designing a
conducive extracellular environment requires better understanding of the role of
biological, chemical, and physical stimuli that may infl uence the structural integrity
and functionality of the engineered tissue. Use of biodegradable polymer scaffolds
is generally preferred because the polymer scaffolds can serve as a template for tis-
sue development and the scaffolds are resorbed, avoiding foreign body response.
For example, collagen-based hydrogel has been extensively used as a scaffold for
tissue engineering. There are several advantages for using the collagen-based scaf-
fold. First, as described earlier, collagen is the principal component of in vivo ECM.
Second, it provides a suitable microenvironment for cells, including large pores and
high mechanical strength (Friess
1998
; Yannas
1995
). Third, cells can be directly
incorporated into the collagen monomeric solution. Fourth, by varying the scaffold
composition, the mesh size is controlled, and the optimal scaffold composition may
be determined for engineering a specifi c tissue type. Fifth, collagen scaffold can be
served a model to study the complex tissue development as the seeded cells interact
