Biomedical Engineering Reference
In-Depth Information
large area with little donor skin. Using computerized planimetry, measurements of
donor biopsy size and area treated with CSS are made and indicate wounds closed
with CSS cover on average 61.5 ± 8.4 times the area of the donor biopsy.
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These
values demonstrate the reduction of donor skin harvesting by grafting of CSS in
place of AG. In order for CSS to be effective, the grafts must have a high
engraftment rate. Percent engraftment at post operative day 14 was 79.5 ± 2.1% for
CSS and 97.5 ± 2.0% for AG. These data demonstrate comparable rates of
engraftment for CSS and AG and that 1% total body surface area (TBSA) of donor
skin can close ~60% TBSA of excised burn. This result defines a new medical
benefit for burn patients by autologous CSS with reduction of donor skin harvest-
ing to complete wound closure.
12.5.2
Qualitative assessment
Qualitative outcomes, which rely heavily on the trained eye of the clinician, can be
assessed through clinical evaluation integrating multiple properties of the wound.
For example, the Vancouver Scale is used to assess burn scar and provides an
ordinal score for properties of the skin such as pigmentation, vascularity, pliability
and scar height.
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Such scales assign quantitative values to qualitative measure-
ments and can provide a relative comparison for evaluation. Vancouver scores for
CSS have been shown to be statistically lower than AG during the first six months
after grafting and not different at one year or after.
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12.6 Regulatory issues
Within the United States, the Food and Drug Administration (FDA) regulates the
protection of the public from health risks associated with new medical therapies.
FDA approval requires that new therapies be safe and effective and that the
probable benefits to health outweigh the probable risks of the therapy or of the
untreated disease condition.
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Safety considerations for cultured skin substitutes
must take several factors into account including media composition, tissue acqui-
sition, graft fabrication and storage, and sterility testing of the final product.
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For
example, in an effort to reduce the potential risk of exposure to and transmission
of bovine spongiform encephalopathy (BSE), the FDA recently proposed a
regulation that would prohibit the use of certain cattle materials, including the
brain, skull, eyes and spinal cord, in the manufacture of medical devices intended
for use in humans.
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Thus, efforts have been made to develop a defined animal-
product free medium for use with cell culture to avoid potential prion infections
associated with growth factor extracts such as bovine pituitary extract, a common
component of keratinocyte growth medium.
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In addition, the methods used to
propagate primary isolations of keratinocytes for cultured skin substitutes have
changed in response to changes in FDA guidelines for medical devices. In 2003,
the Department of Health and Human Services defined xenotransplantation as
