Biomedical Engineering Reference
In-Depth Information
Rudolph 1979; Breuing et al. 1992; Carver et al. 1993a; Kangesu et al. 1993a; Orgill
et al. 1996). Later studies have emphasized the mouse (murine) model in order to
take advantage of numerous transgenic strains that have become available with this
species (Chen et al. 2013).
Porcine skin approximates human skin more closely than does rodent skin in
thickness, hair follicle density, and firmness of attachment to the underlying tissues
(Hartwell 1955; Kangesu et al. 1993a). The last feature probably accounts for the
significantly smaller extent of wound contraction in full-thickness porcine wounds
compared to rodent wounds of the same depth. In addition, as many as 30 wounds
(Breuing et al. 1992) can be studied on the extensive dorsal surface of the Yorkshire
pig (mini pig). Several comparisons between the two models, rodent and swine,
have been drawn (Hartwell 1955; Rudolph 1979; Kangesu et al. 1993a; Compton
1994; Orgill et al. 1996). A major structural difference between human and porcine
skin is lack of eccrine sweat glands and an abundance of apocrine glands (Winter
1972; Compton 1994) as well as a paucity of elastin fibers and vasculature in the
swine (Kangesu et al. 1993a). Furthermore, unlike human skin, porcine skin has an
elastic membrane in the hypodermis and an underlying panniculus carnosus muscle
(Kangesu et al. 1993a). The small size and relatively slow growth rate of the guinea
pig, and of other small rodents, make them convenient for long-term studies or in
tests of the average response of a population of animals to a wound-healing treat-
ment (Orgill et al. 1996). In contrast, the larger Yorkshire pig, which grows very
rapidly making its study cumbersome, offers a size advantage in detailed studies
of wound fluid composition, especially when wound chambers are used (Eriks-
son et al. 1989; Breuing et al. 1992). Another advantage of the swine model is the
relatively small contribution of contraction in wound closure relative to the rodent
models, making the swine wound-healing behavior similar in this respect to the hu-
man (Rudolph 1979). Reviews of wound-healing models in different species have
been presented (Cohen 1991; Hayward and Robson 1991).
The skin wound that is perhaps most free of contraction in the adult mammal is
the dermis-free defect in the rabbit ear, discovered during a search for a model that
could be used to study epidermal migration in the absence of contraction (Vorontso-
va and Liosner 1960; Joseph and Dyson 1966; Goss 1992). A specific rabbit ear
model of wound healing (dermal ulcers model) has been described in great detail
(Mustoe et al. 1991; Jia et al. 2011). Briefly, the dermis and epidermis are excised
down to the depth of bare cartilage, an avascular tissue, and the perichondrium is
also removed; new granulation tissue arises, therefore, entirely from the periphery
of the wound rather than from the tissue below, as in dermis-free defects in other
anatomical sites. Contraction of skin is not observed in this wound model (Mustoe
et al. 1991).
An unusual mouse species, MRL/MpJ, which heals without scarring the injured
cartilage in through-and-through ear punch wounds, was discovered (McBrearty
et al. 1998) and has since been studied for clues to the molecular basis of regenera-
tion processes in mammals. MRL/MpJ mice nevertheless heal dorsal skin wounds
by scar just as other mouse species do (Li et al. 2000; Colwell et al. 2006). MRL/
MpJ mice have been studied in a search for candidate genes for wound healing by
