Biomedical Engineering Reference
In-Depth Information
(a)
(b)
12.3
SEM images of collagen-GAG sponge. Scale bar = 1 mm (a) =
50 µm (b).
dehydrothermally crosslinked at 140 ºC for 24 hours,
47-49
packaged and steri-
lized by gamma irradiation and stored for later use.
12.3.3
Fabrication of cell-polymer constructs from multiple
cell types
As the primary goal of a skin substitute is wound closure, keratinocytes are the
essential cellular component of the skin substitute. The importance of a dermal
component in skin substitutes, not only for ease of transplantation but also for
in
vitro
epidermal development is now well recognized. The role played by fibroblasts
has been supported by several investigators who showed that diffusible factors
released by fibroblasts regulate epidermal morphogenesis.
50
It has also been
widely recognized that for optimal functional and aesthetic outcomes both
keratinocytes and fibroblasts are needed.
51,52
Cultured skin substitutes (CSS)
consist of a freeze-dried, lyophilized collagen-glycosaminoglycan (GAG) sponge
populated with autologous keratinocytes and fibroblasts. Fibroblasts and
keratinocytes are serially inoculated into a collagen-based scaffold at high densi-
ties
48,53,54
to promote organization of the dermal and epidermal layers. Keratinocytes
and fibroblasts have been shown to self-organize when exposed to an air-liquid
interface, however the self-organization process increases the time from graft
fabrication to patient application.
23
CSS are cultured at the air-liquid interface for
9 to 14 days to provide a liquid to gas transition with nutrient medium contacting
the dermal substitute and air contacting the epidermal substitute, resulting in
stratification and cornification of the keratinocyte layer.
55-58
In the dermal layer
fibroblasts fill the collagen sponge, begin to degrade it and generate a new
extracellular matrix. At the dermal-epidermal junction, evidence of basement
membrane formation
in vitro
has also been demonstrated.
59
Thus, the blistering
encountered with cultured epithelial autografts is not a clinical complication after
grafting of CSS because the maturation of the dermal-epidermal junction is
accomplished before grafting.
