Biomedical Engineering Reference
In-Depth Information
4
Experimental Methods II. The Defect
Closure Rule
4.1
Total Resulting Change Following Healing Versus
Mechanism of Healing
In the preceding chapter we discussed the experimental space required for a study of
regeneration. The next questions to settle are: How long should the study last? And,
what exactly will be measured at the end?
It has been pointed out that biology is intrinsically different from physics in that
it is impossible to understand a living organism without knowing its evolutionary
history; in contrast, a system in physics can be adequately defined in terms of its
current state, without knowing the path that led to this state (Mayr 1997). This
distinction repeats the main theme in Darwin's seminal text. The pioneering author
made it clear that he was not interested in adding his own voice to the polyphony
of contemporary authors who were advancing their views about the overall location
of a species in the architecture of natural order; instead, he was simply interested
to establish a model about the pathway that led to the current physiological status
of a species (Darwin 1872). The argument made above is that a biological process,
such as evolution, cannot be understood without clear knowledge of its detailed
mechanism. Obviously, this argument applies to the healing process of a defect as
well. The structure of the healed tissue cannot be completely appreciated without
knowledge of the mechanism by which healing occurred.
There is no doubt that discussions of mechanism inspire and motivate investi-
gators. Nevertheless, and while the specific mechanism by which regeneration is
induced is discussed and debated in later chapters, there is need for reliable quan-
titative relationships between specific experimental manipulations of the healing
process of a defect and the resulting changes in outcome. Such empirical data are
required beyond the need for development of improved clinical treatments of organ
healing; if solidly supported by the evidence, these input-output relationships can
also be used as the reliable benchmarks by which to compare hypothetical mecha-
nisms of regeneration.
