Biomedical Engineering Reference
In-Depth Information
in cases of skin loss or peripheral nerve loss are currently being pursued. This
chapter outlines the basic principles that are currently known to govern processes
of induced organ regeneration, especially skin, in the adult mammal.
14.2
The central problem of skin regeneration
The topic of organ regeneration is best introduced by distinguishing the tissue
types in a given organ that regenerate spontaneously from those that do not. This
distinction is essential: tissues, rather than the entire organ, which does not
regenerate spontaneously, become the focus of the discussion, leading to an
enormous simplification of the problem of induced organ regeneration.
Although this chapter focuses on skin regeneration, frequent references will
be made to peripheral nerve regeneration. The regenerative behavior of these
two organs, skin and peripheral nerves, has been studied much more extensively
than that of other organs (with the exception of studies of the liver). Data from
these two organ sources are abundantly available; such data are largely missing
for other organs. In addition, striking similarities have been identified between
the mechanism by which regeneration is induced in skin and nerves. This
identification has solidified the conceptual basis of induced regeneration in
adults and has suggested methodology for extending the regenerative treatment
to other organs as well.
The spontaneous response of organs to injury can be interpreted by referring
to the healing response of the 'tissue triad'. Three tissue types, epithelia, base-
ment membrane and stroma, are grouped together in anatomical proximity in
most organs. The response of different organs to injury can be readily analyzed,
and eventually generalized, by reference to the response of these anatomical
structures. The epithelia (epidermis in skin, myelin sheath in nerves) regenerates
spontaneously provided the stroma is intact and, while doing so, induce regen-
eration of the attached basement membrane. The stroma (dermis in skin,
endoneurium in nerves) is non-regenerative, that is, it does not regenerate spon-
taneously in adults. Once the dermis has been induced to regenerate, the
epidermis and basement membrane regenerate spontaneously. It follows that
regeneration of the stroma is the major problem in studies of induced regenera-
tion of the skin.
14.3
Experimental variables in studies of skin
regeneration
Since experimental studies of induced skin regeneration must necessarily focus
on regeneration of the dermis following an injury, it follows that the experimen-
tal space for the study should be an injury (wound) in which the native dermis is
clearly absent, for example removed by excision. Such a wound is the anatomi-
cally well-defined full-thickness skin wound, prepared by complete excision of
