Biomedical Engineering Reference
In-Depth Information
fibroblast axes become oriented along the direction of the major contraction
vector. Collagen fibers synthesized by these oriented cells should therefore also be
oriented along the same major axis. During skin wound healing there is evidence
that a mechanical tensile field (a plane stress field) does indeed develop in the plane
of the wound (Yannas, 2001). Quantitative measurement of the orientation of
collagen fibers in dermal scars by laser light scattering showed that the fibers were
persistently oriented in the plane of the wound and along the direction of the major
contraction vector of the wound rather than being quasi-randomly oriented, as in
physiological dermis (Ferdman and Yannas, 1993).
These considerations suggest the hypothesis that scar formation is the product of
collagen fiber synthesis in the presence of the tensile field generated by a wound
contraction process. According to this hypothesis, fiber orientation, one of the
hallmarks of scarring, should accordingly disappear following cancellation of the
tensile mechanical field in the plane of the wound. Blocking of contraction by an
appropriate scaffold should cancel such a mechanical field and should block
synthesis of oriented fibers (scar). In fact, when scaffolds that block contraction,
even to a relatively minor extent, have been used, scar could not be detected in the
closed wound (Yannas, 1981; Yannas
et al
., 1981, 1982a,b, 1984, 1989). How-
ever, observations of a lack of scar in the closed wound have so far been estimates
based on histological data from a very limited number of tissue sections viewed in
the microscope and do not support a firm, quantitative conclusion about the
absence of macroscopic scar tissue. There is need for data of a much more
extensive and quantitative nature to test the hypothesis that scar formation depends
on the presence of wound contraction and that abolition of scar depends largely on
cancellation of the mechanical field of contraction.
14.6 Experimental studies of partial regeneration of
skin
There is accumulating evidence that the healing process of an injured organ in the
adult mammal can be modified to yield a partly or wholly regenerated organ. In
almost all processes studied to date, the critical 'reactant' supplied by the investi-
gators was a scaffold synthesized as an analog of the extracellular matrix (ECM),
occasionally seeded with autologous epithelial cells.
A detailed example of induced skin regeneration, originally referred to as
synthesis of an 'artificial skin' (Yannas and Burke, 1980), has been described
elsewhere (Yannas
et al
., 1981, 1982a,b, 1984, 1989; Murphy
et al
., 1990; Butler
et al
., 1998, 1999; Orgill and Yannas, 1998; Compton
et al
., 1998). The data
describe in substantial detail the structural and functional similarities, as well as
differences, between normal skin, scar and regenerated skin in the adult guinea pig
and the swine following grafting of dermis-free defects with the keratinocyte-
seeded dermis regeneration template (DRT), a scaffold characterized by unusual
regenerative activity. DRT is a macromolecular network synthesized as a highly
