Biomedical Engineering Reference
In-Depth Information
confluent cultures, also appeared to demonstrate improved take. However, as only
two patients were treated in this study, and different sites were treated with
inconsistent methods, no firm conclusions were drawn. Despite this, when sub-
confluent keratinocytes were delivered with the cell sheet down, take rates of 87%
were observed suggesting that the technique provided good biological and me-
chanical support for keratinocytes.
The same group conducted further investigations using an athymic mouse
model to assess better the effect that cell culture conditions have on successful
wound repair (Ronfard
et al
., 2000). In additional clinical studies it was found that
cell spreading was reduced when keratinocytes were cultured on a fibrin matrix
compared with tissue culture plastic, although the clonogenic capacity of the fibrin
matrix was similar. The fibrin matrix was found to have completely degraded
within 11 days following transplantation onto the mouse model. As part of this
study, seven patients suffering from burns ranging from 45-95% total body
surface area (TBSA) were treated with keratinocytes cultured on fibrin matrices.
Histological examinations of punch biopsies demonstrated that structures analo-
gous to rete ridges were present in areas treated with fibrin matrix but were not
present in areas treated with cultured epithelium alone, suggesting that the pres-
ence of the fibrin matrix may facilitate the formation of dermal/epidermal junctions.
These studies demonstrated, above all, that the use of fibrin as a carrier matrix
improves the mechanical integrity of CEAs and acts as an ideal carrier material.
Additionally, the fibrin matrix was found to retain its size in contrast to CEA which
can shrink to one-third of its original area prior to application, therefore allowing
greater areas to be treated. Fibrin matrices were also found to be strong and capable
of being easily moulded to complex contours.
As a delivery vehicle for keratinocytes, a matrix is required to maintain a
population of stem cells or holoclones from which transiently amplifying cells, and
ultimately differentiated keratinocytes, can proliferate. A study by Pellegrini
et al
.
(1999) aimed to establish whether keratinocytes, cultured on a fibrin matrix,
maintained their clonogenic capacity, growth rate and long term proliferative
potential. This study demonstrated that keratinocytes delivered on fibrin sheets
maintained a clonogenic potential and that cultured autografts containing stem
cells can rapidly, and permanently, cover the surface of wounds with epithelium.
Conventional light and transmission electron microscopy (TEM) verified that all
of the structural components of the dermal-epidermal junction were present, that
is the hemidesmosome-anchoring filament complexes, the basal lamina and the
anchoring fibrils. In addition, melanocytes were present, as were Langerhans cells
which are known to be lost in keratinocyte culture. This suggests repopulation
from the underlying wound bed. Clinical studies demonstrated excellent take rate
and an epidermis which was stable 2-20 months postoperatively. The authors also
examined the cost of using fibrin matrix which was found to be approximately 50%
of the cost of CEA owing to the reduced amount of handling during culture and the
greater area that could be covered.
