Biomedical Engineering Reference
In-Depth Information
8
An Antagonistic Relation Between
Wound Contraction and Regeneration
8.1
Search for the Mechanism of Regenerative Activity
In the preceding chapters, we describe the outcome of various healing processes in
which repair was replaced by regeneration. We concluded, for example, that stroma
regeneration is the central problem in regenerative science as stroma is the key tis-
sue that fails to regenerate spontaneously during healing in adults (Chap. 2). Other
tissues of an organ, mainly epithelial tissues and basement membrane, regenerate
spontaneously provided stroma is present in healing skin wounds (Chap. 5) and
wounds in peripheral nerves (Chap. 6).
What exactly is the mechanism of repair that apparently prevents regeneration
from happening spontaneously in injured sites? To answer this question, we probe
into two processes by which wounds close spontaneously in adults: contraction and
scar formation.
Contraction of tissues is usually overlooked in the literature of wound healing.
Difficulties in measurement of tissue dimensions during healing are an important
contributor to such a neglect. However, several quantitative observations suggest
that contraction is a significant, often dominant, mode of wound closure in many
species. A compilation of quantitative literature data shows that wound closure by
contraction is often the dominant mode compared to scar formation, especially in
rodents (Table 4.3). In rodents, skin wounds contraction accounts for 88-96 % of
closure of the initial wound area (Kennedy and Cliff 1979), although contraction
closes a lower fraction of the initial wound area in the swine. Scar formation has
been also greatly overlooked in the literature.
In this chapter, we show first that contraction of wounds is reported to be strongly
blocked or absent in a number of studies of well-known models of injury which heal
spontaneously by regeneration. These examples include healing of skin wounds in
the developing frog, the rabbit ear, the oral mucosa of the adult human, and even the
axolotl, the exemplary model of perfect regeneration.
We then review the evidence from the studies with adult mammalian wound
healing models which normally heal by repair. We find that spontaneous contraction
