Biomedical Engineering Reference
In-Depth Information
constant for the regeneration processes that we have examined in preceding chap-
ters. If so, this constant background can be omitted from reaction diagrams without
affecting our judgment on the relative simplicity of protocols used by different in-
vestigators who studied the same defect. The reaction diagram includes reference to
soluble reactants (e.g., cytokines) that have been added but omits reference to any
soluble products that may have been synthesized during the process. As the products
of main interest in these processes are the (insoluble) tissues that are synthesized,
such omission does not affect a conclusion on the relative simplicity or effective-
ness of a protocol. Previously, a myriad of authors describing biological processes
have selectively omitted information such as, for example, the temperature and the
pH levels of an in vivo study; both of these parameters are widely considered, with
very few exceptions, to have remained at physiological levels during each of several
studies conducted. As they comprise a common background in different investiga-
tions, these parameters are often omitted, even from a detailed discussion of the
experimental conditions.
It is important to clearly distinguish between a reaction diagram and a chemical
equation. As used here, reaction diagrams are shorthand descriptions of a proto-
col used by the investigators. They do not contain stoichiometric information and
should, therefore, be considered somewhat analogous to qualitative, unbalanced
chemical equations. The symbols employed on both sides of the arrow in a reaction
diagram simply identify a given protocol, namely, the addition of a reactant or the
synthesis of a product, not the relative masses of reactants or products. It is a quali-
tative tally of what went in the defect and what came out.
A reaction diagram based on data reported in the literature usually does not de-
scribe the simplest process by which a tissue or organ can be prepared. However,
comparison of several reaction diagrams can lead to an irreducible reaction dia-
gram, i.e., a description of the simplest known process by which the synthesis has
been achieved. For example, let us hypothesize that tissue C, synthesized as shown
in Dg. A previously, can also be synthesized by a simpler route:
cell type A
→
tissue C
(Dg. B)
If Dg. B is indeed the simplest route reported in the literature, the diagram repre-
senting it will be considered to be the irreducible reaction diagram for synthesis
of C. In a comparison of two reaction diagrams for synthesis of the same tissue or
organ, the one using fewer reactants will obviously be considered simpler. Between
two protocols that make use of the same number of reactants, that which employs
fewer cell types will be considered simpler; also, in vitro conditions will be consid-
ered to be simpler than in vivo conditions.
Once identified, the irreducible diagram suggests the minimal conditions known
for synthesis of the product(s). Such an identification obviously cannot be used to
assert that even simpler conditions cannot or will not be discovered at a later time
when future investigators may come to understand much more clearly the nature of
these synthetic processes. However, the irreducible process does contain the answer
to the following important question: Based on the data available to us today, which
