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Exploring human organs with computers 153

9.3 Designing drugs
Car crashworthiness design involves the manufacture of a new system, but
each stage of the process requires an understanding of the operation of an
existing system. This is analogous to most research in biology. However,
in contrast to crashworthiness design, investigations into the operation of
biological organs are still dominated by experimental approaches. There
are some exceptions, such as in the development of therapeutic drugs to
combat disease. In the past this was performed purely in a brute-force trial-
and-error manner. Cell cultures, animals or humans were subjected to
many variations of a likely candidate for a drug, with the final choice being
chosen on the basis of best performance with the minimum adverse side
affects. This is analogous to building thousands of car prototypes simulta-
neously, each with slight differences in design, and then subjecting them
all to the rigors of experimental crash testing. The best model is that
which, largely by chance, survives best. If car crashworthiness was still
designed in this way, only the very rich would be able to afford the end
product. Fortunately, computer models are now being used to ‘experiment’
with the effects that changes in structure will have on the potency of the
drug, with corresponding reductions in production costs.
Each organ in the human body plays a crucial life-sustaining role, and
understanding how each works is of profound interest for many reasons,
from the possibility of widespread treatment, or even the prevention of
disease, to the possible engineering applications of the unique types of
signal processing employed by each organ. It is natural to describe the func-
tion of an organ, and hence model its behaviours, in terms of the compo-
nents at the next level down in the biological hierarcy, the cell (Figure 9.2).
Both the behaviour of the cells in isolation and all of the interactions
between them must be considered. A finite-element computer model that
represents an organ at the level of the cell allows us to observe the individ-
ual interactions between tens of thousands of cells simultaneously. Such
experiments are impossible to perform on the real system. Finite-element
modelling of biological systems has already begun in a number of areas,
including bone, skin and brain mechanics, intercellular communication
within tissues, and heart contraction.