Regeneration of Skin - Tissue and Organ Regeneration in Adults - page 104

Fig. 5.2 Contraction kinetics following grafting with cell-free and cell-seeded DRT. The dermis-
free defect in the guinea pig was grafted with a analog B, an ECM analog identical to DRT in
structure except with average pore diameter 450 µm (inactive ECM analog), b keratinocyte-seeded
dermis regeneration template (KC + DRT); c cell-free DRT. Cell-free DRT delayed contraction
but did not arrest it; eventually, only a small mass of dermis was synthesized. KC-seeded DRT
arrested contraction at 35-40th day and the defect perimeter continued increasing at a rate higher
than predicted by animal growth to yield a partial skin regenerate (appendages missing) occupying
two thirds of initial defect area at day 200. (Source: Yannas et al. 1989)
area; the remainder, about 12 % of initial defect area, eventually closed by epitheli-
alization. Underneath this epithelialized layer was a small mass of connective tissue
that was tentatively labeled “neodermis” on the evidence that it comprised loosely
packed collagen fibers. These features stood in contrast to scar tissue, comprising
tightly packed collagen fibers, that formed in ungrafted controls underneath the
newly epithelialized area (Yannas 1981; Yannas et al. 1981 1982b).
Subsequent studies confirmed that loss of regenerative activity of the ECM ana-
log occurred when either the chemical composition, half-life for degradation or
average pore diameter were each displaced from a rather narrow range, as described
further in Chaps. 8 and 9 (Yannas et al. 1982b, 1989). The combined results sug-
gested very strongly that the ECM analog induced regeneration of a dermis in the
guinea pig and that regeneration did not occur unless the structure of the ECM ana-
log was tightly controlled within narrow limits (Yannas et al. 1989; Murphy et al.
1990). These results suggested the specific name DRT for the active ECM analog.
The magnitude of defect contraction on the regenerative activity of DRT was
studied by comparing closure of defects in the guinea pig and the swine, two spe-
cies which show different wound contraction behavior. As expected from data in
Table 5.3 , a dermis-free defect in the swine spontaneously closed by contraction
to a lower extent than in the guinea pig. It was observed that DRT significantly
delayed the onset of contraction in both animal models. At the end of the study, at
day 21, histological data showed a new bed of thick collagen bundles, randomly
oriented, resembling dermis rather than scar, both in the guinea pig and the swine
models (Orgill et al. 1996). By day 21, grafted defects in the guinea pig had closed