Biomedical Engineering Reference
In-Depth Information
prick test) gave positive results in both normal and regenerated skin (Yannas et al.
1981, 1982a, b, 1984, 1989; Orgill 1983; Murphy et al. 1990).
There were also differences between regenerated skin and normal skin
(Table
5.2
). The axes of collagen fibers in the regenerate were significantly less
randomly oriented with respect to the plane of the epidermis (
S
= 0.48 ± 0.05;
n
= 5
animals) than in normal skin (
S
= 0.20 ± 0.11;
n
= 21;
p
< 0.001;
S
= 1 for ideally ran-
dom orientation and 0 for perfect orientation). The diameter of collagen fibers in the
regenerate was smaller (15 ± 10 μm;
n
= 5 animals) than in normal skin (26 ± 13 μm;
n
= 21 animals;
p
< 0.10). The tensile strength of regenerated dermis (14 ± 4 MPa;
n
= 3) was significantly lower than that of normal skin (31 ± 4 MPa;
n
= 4;
p
< 0.01).
The rete ridge pattern in normal skin was somewhat more complex than that in
regenerated skin. Unlike normal skin, there were no skin appendages (e.g., hair fol-
licles, sweat glands) in the regenerate (
n
> 100 fields) (Yannas et al. 1981, 1982a, b,
1984, 1989; Orgill 1983; Murphy et al. 1990; Compton et al. 1998). Although less
extensive, the morphological characteristics of skin synthesized in the swine model
were generally similar to those reported with the guinea pig model.
The regenerated skin was not a scar in a number of significant respects. In scar,
the dermoepidermal junction was not well-formed, lacking rete ridges with the asso-
ciated dermal papillae, as well as lacking capillary loops in the papillae; in contrast,
regenerated guinea pig skin had all of these features (
n
> 100 fields) (Table
5.2
). The
subpapillary microvasculature, consisting mostly of venules, that was present in re-
generated skin, was absent in scar (Fig.
5.5
). Unmyelinated nerves associated with
the dermal papillae were present in the regenerate but missing from scar (
n
> 100
fields). Orientation of collagen fibers in the plane of the epidermis was described in
terms of the orientation index
S
, measured by laser light scattering, that varies from
0 (random alignment of fibers) to 1 (perfect alignment). Collagen fibers in the partly
regenerated dermis were significantly less oriented in the plane of the epidermis
(
S
= 0.48 ± 0.05;
n
= 5) than in scar (
S
= 0.75 ± 0.10;
n
= 7;
p
< 0.001). However, the
average diameter of collagen fibers in the regenerate (15 ± 10 μm;
n
= 5 animals)
was not significantly different than that in scar (11 ± 8 μm;
n
= 7;
p
< 0.5). Neither re-
generated skin nor scar possessed epidermal appendages (e.g., hair follicles, sweat
glands) (
n
> 100 fields) (Yannas et al. 1981, 1982a, b, 1984, 1989; Orgill 1983;
Murphy et al. 1990; Compton et al. 1998).
In summary, the morphological and functional data presented in Table
5.2
,
Figs.
5.3
,
5.4
, and
5.5
, and analyzed above can be summarized as follows: Regener-
ated guinea pig skin and regenerated porcine skin are clearly different from scar;
they can be best described as an imperfectly synthesized skin.
5.5
Synthesis of Hair Follicles and Sebaceous Glands
A deficiency of skin synthesized using DRT seeded with epidermal cells has been
due to lack of hair follicles and of other skin appendages, primarily sweat glands
(see above). In this section we describe ongoing studies which have led to the syn-
thesis of hair follicles in experimental animals.
