Biomedical Engineering Reference
In-Depth Information
than in intact skin. In addition, the cleavage plane of the blister at the site of KC
sheet grafting was below the lamina densa of the BM while failure occurred above
it in normal skin. The BM zone beneath the KC sheet grafts was found to lack a
component of type IV collagen, known as 7-S sites, as well as anchoring fibrils that
are present in normal skin (Woodley et al. 1988a). Results from a five-patient study
showed that the tissue layer that formed in the subepidermal region contained most
of the major macromolecular components of connective tissue; exceptions were the
paucity of elastin fibers and poor organization of the protein linkin (microthread-
like fibers). It was suggested that structural abnormalities of skin were responsi-
ble for the observed fragility of skin that formed following grafting of KC sheets
(Woodley et al. 1990). Additional evidence showing that grafting of full-thickness
skin defects with KC sheets leads to strongly delayed synthesis of the BM, as late as
within 4-5 weeks, was described in a study of burn patients (Mommaas et al. 1992).
The morphological interpretation of detachment of the epidermis was pursued
in some detail in the swine model (Carver et al. 1993b). The two surfaces resulting
from avulsion of grafted KC sheets were observed by electron microscopy. The
cleavage plane was found to lie between the reticular layer of the BM and the upper-
most part of the granulation tissue of the two-week-old defect surface. Specifically,
basal KC, lamina lucida, lamina densa and anchoring fibrils were all attached to the
avulsed epidermis, while collagen fibers remained with the fibroblasts in the granu-
lation tissue in the defect. The authors concluded that the mechanical weakness
of the dermoepidermal junction was due to lack of integration of dermal collagen
fibers with anchoring fibrils in the reticular layer of the BM. In contrast, a study of
normal skin controls showed that an abundance of dermal collagen fibers was inter-
twined with the anchoring fibrils of the BM. The description of the sub-epidermal
region at day 27 after grafting KC sheets showed that collagen synthesis had taken
place and that new capillaries had also formed very close, within 20 mm, to the epi-
dermis; however, collagen fiber bundles were not well organized immediately be-
neath the BM. The authors eventually concluded that the reported clinical problems
with attachment of KC sheet grafts was related both in maturation delay of the BM
as well as in poor integration with collagen of the wound bed (Carver et al. 1993b).
In another study, in which the KC sheets were grafted on dermis-free defects in
athymic mice, half of the keratinocyte grafts showed blistering at days 20 and 42
(Cooper et al. 1993). Large areas of separation of the epidermis from the subepi-
dermal region were observed over the 20-day period following grafting with the
keratinocyte sheets; however, by day 42 no separation was seen at the subepider-
mal region. At day 42, light microscopy revealed a persistently immature epidermis
without rete ridge formation while immunohistochemical staining for type IV col-
lagen showed discontinuous staining, consistent with disruption of the BM at the
points of discontinuity. Electron microscopy showed little evidence of anchoring fi-
brils as well as a discontinuity in the basal lamina by day 20; however, at day 42, the
basal lamina had become continuous. The morphology of the subepidermal region
was not described in this study; however, blood vessels were observed underneath
the keratinocyte graft at day 10 (Cooper et al. 1993). Later reports of clinical stud-
ies based on use of cultured epithelial autografts have focused on the vulnerability
