Biomedical Engineering Reference
In-Depth Information
Table 7.3
Reactants required for synthesis of skin, peripheral nerves and their tissue components
Skin
Peripheral nerve
Tissue
Reactant
required for
synthesis
Reaction
conditions
Tissue
Reactant
required for
synthesis
Reaction
conditions
Epidermis
Keratinocytes In vitro
d
Myelin
sheath
f
Schwann
cells
f
In vitro
d
BM
Keratinocytes In vitro
d
BM
Schwann cells In vitro
d
Dermis
a
DRT
c
In vivo
e
Endoneurium Not observed Not observed
Skin
b
Keratinocytes;
DRT
In vivo
e
Nerve trunk
g
Tube
h
In vivo
i
BM
Basement membrane
a
Synthesized dermis had dermal papillae, elastic fibers and dermal nerve fibers
b
Synthesized skin had a keratinizing epidermis, basement membrane and dermis. Skin append-
ages were synthesized by seeding DRT with cells from dermal papillae
c
DRT, dermis regeneration template, a highly porous graft copolymer of type I collagen and
chondroitin 6-sulfate with defined network structure
d
Synthesized in culture medium
e
Synthesized in a dermis-free defect
f
Neurons, with axonal processes, were also present but not considered a reactant during synthe-
sis of myelin sheath by Schwann cells on axonal surface (myelination) (see text)
g
Nerve trunk comprised conducting nerve fibers across entire length
h
Tube bridged gap between transected nerve stumps; tube wall commonly consisted of silicone,
synthetic polymers or collagen
i
Synthesized inside tube bridging transected nerve stumps
layer. Unassisted by cells of another type, keratinocytes and Schwann cells each
eventually condensed in culture and differentiated to form their respective avascular
layer as well as the associated BM. To synthesize the stroma (dermis), however, an
appropriate nondiffusible regulator as well as in vivo conditions were both required
(data on endoneurium synthesis are unavailable). Both in skin and peripheral nerve,
the dividing line between in vitro and in vivo protocols has been the BM. Consid-
ering for a moment the regenerative character of the tissues involved, we further
conclude that the spontaneously regenerative tissues, the epidermis and the myelin
sheath, were synthesized in vitro while synthesis of the nonregenerative tissue (der-
mis) required in vivo conditions (Yannas 2000) (Fig.
7.2
).
7.6
Toward Simple Protocols for Synthesis of the Entire Organ.
I. Modular Synthesis of Epithelial Tissues and Stroma
Consideration of the tissue triad inspires similarities in protocols for synthesis of
individual tissue components in several organs. Even though located in organs other
than skin or peripheral nerves, these tissue components occupy the same relative
anatomical position in the tissue triad that characterizes an organ. This approach
appears to serve as a key that opens the door to regeneration in other organs.
