Biomedical Engineering Reference
In-Depth Information
using STSG in patients with small wounds but closure is challenging in large burns
owing to limited donor sites. Prompt wound coverage in these patients is essential
to decrease the probability of infection and sepsis which are major causes of burn
mortality.
6
Conversely, chronic wounds tend to involve relatively small areas of skin but
represent a major medical need as they have a high incidence in the general
population. The most common chronic wounds are pressure ulcers and leg ulcers.
7
These wounds affect more than 2 million people
8
and are estimated to cost US$1
billion annually.
7
Historically, wound closure has been enhanced with topical
agents such as growth factors to stimulate healing and antimicrobial agents to
minimize infection.
9
A large percentage of these patients will ultimately require
grafting with split- or full-thickness autograft for permanent closure of chronic
wounds. However, autograft may not be a feasible option in these patients owing
to the underling deficiencies in wound healing which compromise healing in donor
sites. A medical need clearly exists for a safe and effective therapy of both acute
and chronic wounds, and thus is a major motivation for the design of bioengineered
skin substitutes.
12.2 Medical and surgical objectives for cultured skin
substitutes (CSS)
Normal human skin performs a wide variety of protective, perceptive and regula-
tory functions that help the body maintain homeostasis. Ideally, a skin substitute
should restore the anatomy and physiology of uninjured skin. However, there are
currently no skin substitutes which fully replicate all of the structures and functions
of native skin.
10-13
Although skin substitutes cannot restore all the functions of
normal human skin, they can provide several advantages over conventional
therapy including reduction in donor site area required to close wounds perma-
nently. For example, conventional grafting expands donor skin by about 1:4. In
contrast, rapid growth of cells
in vitro
allows coverage of culture surfaces by more
than 1000 times the area of the skin biopsy
14,15
and cultured skin substitutes have
been shown to heal approximately 60 times the area of the initial skin biopsy.
16
Therefore, skin substitutes containing autologous keratinocytes are ideal candi-
dates for acute injuries where donor sites are limited. By increasing the availability
of grafts for wound coverage, autologous skin substitutes can provide several
advantages over conventional therapy including reduction in the donor site area
required to close wounds permanently, reduction in the number of surgical
procedures and hospitalization time and reduction of mortality and morbidity from
scarring.
17,18
The re-establishment of the epidermal barrier to fluid loss and microorganisms
19
is one of the most important objectives for an engineered skin substitute. Ideally,
a skin substitute should be readily available, easy to apply, promote complete
engraftment without contraction, allow rapid healing forming both dermal and
