Biomedical Engineering Reference
In-Depth Information
seeded DRTs have been shown to arrest (and possibly reverse) contraction
altogether, allowing for a greater degree of regeneration.
37
Although they lack
appendages, adequately healed DRT-treated tissues 'look and feel' similar to
normal skin.
Spatial, mechanical and biological considerations for scaffolds
For cutaneous wounds to regenerate, the geometric properties of both the defect
and the material (used to patch the defect) are of paramount importance.
41
The
defect should have unambiguous, physically contained anatomical boundaries that
prevent loss of exudates, as well as entry of bacteria and extraneous tissues. A full-
thickness (no dermis remaining) wound would satisfy this criteria, whereas a
partial-thickness wound (some dermis remaining) would not.
In general, mechanical properties of DRTs should resemble those of normal
skin.
23, 41
DRTs must maintain the elasticity, pliability and durability seen in normal
skin. At the same time, they must rapidly and uniformly adhere to the underlying
tissue. The scaffold pore size (20-125 µm) must not restrict cellular infiltration.
37
Scaffold fibers must allow for cellular attachment. DRTs should be non-toxic and
non-antigenic, such that a minimal immune response is elicited. They should also
be biodegradable, but stable enough to withstand host enzymes until regeneration
has been irreversibly initiated.
Trophic and growth factors
Trophic factors and pharmacological agents, such as cortisone, prednisone and
aspirin have not been shown to aid regeneration.
41
Likewise, the external applica-
tion of growth factors (including PDGF, bFGF, and TGF-
) has not been shown to
facilitate regeneration. On the contrary, these pro-fibrotic molecules may inhibit
regeneration (as mentioned earlier.)
β
4.7
Issues of stem cells and cellular plasticity
Virtually all tissues in the human body, in theory, have the ability to regenerate.
This ability relies on a group of multipotent adult stem cells that have the capacity
to be self-renewing and to give rise to different cell types.
10,15
Stem cells give rise
to progenitor cells, which are cells that are not self-renewing, but can generate
several types of cells.
The extent of stem cell involvement in cutaneous wound healing is complex and
not fully understood. As alluded to earlier, epidermis and dermis are reconstituted
by mitotically active stem cells that reside in regions within the skin (called
niches.)
10
These regions include the apex of rete ridges,
35
the bulge of hair
follicles
17
and the papillary dermis.
66
Moreover, bone marrow may also contain
stem cells that play a major role in cutaneous wound healing.
12
