Biomedical Engineering
Biomedical Engineering can be
defined as the application of engineering tools and analysis to problems in
medicine. Because this is a broad
definition, it is possible to find biomedical engineers with a broad variety of
backgrounds. Some will come directly
from older disciplines such as Electrical Engineering, Mechanical Engineering,
Chemical Engineering, and Aerospace Engineering. These people become biomedical engineers
because they have a strong interest in medical problems, and they obtain the
knowledge and training that they need to work in this area through a variety of
ways. Others may have two degrees in
engineering and biology, or in related fields.
Formal curricula in Biomedical Engineering have been established in universities
only within the last few decades.
However, Biomedical Engineering has existed for centuries.
One often associates biology
with phenomenalogical non-quantitative descriptions
of anatomy and physiology. For example,
in many universities it is possible to obtain a bachelor of
science degree in biology without having taken even the first course in
the calculus series. It is natural to
ask what a quantitative approach contributes to the field of biology.
Part of the answer to this
question can be found by an examination of a typical hospital. One will find numerous pieces of equipment,
such as magnetic resonance, positron emission, and catscan
imaging systems, ultrasonic scanners, electrocardiograms, insulin monitoring
devices and dialysis machines which must be designed and built by people with
engineering knowledge. This equipment
represents one side of biomedical engineering.
Another side, and to some degree one that is more interesting, involves
the application of engineering analysis to the body itself. Consider the optimization of hip
implants. The implant must last over
decades, and yet a variety of problems can arise that
will either cause the interface between the implant and the bone to degrade or
will cause the bone itself to fracture.
Experimental and computational modeling methods, similar to those used
by mechanical engineers, have been applied to this problem to lead to the
current implementations of these devices.
However, knowledge of mechanical engineering alone is not sufficient to
obtain the kinds of answers that are needed to examine important aspects of the
implant. One must also understand the
physiology of the bone and tissues involved in the problem. In general, the properties of biological
tissues are more complicated than those of engineering materials such as steel
and concrete. They tend to be nonlinear
in the range of conditions in which they are used. They also exhibit properties such as inhomogeneity and non-isotropy.
For an engineer, it is easy
to view the human body as an electrical, mechanical and chemical system. While the nerves in the body are obvious
electrical analogues to wires, biopotentials arise
from a variety of sources, including the contraction of the heart and other
muscles, and the motion of the eyes.
Furthermore, electrical engineering includes the applications of signal
analysis so that any signal derived from the body can be approached from the
point of view of an electrical engineer.
Mechanical engineering is obvious in the hip implant example above, but
this field includes other areas, such as the analysis of walking and running,
and the study of blood flow and its effects on arterial disease. Nonetheless, one can argue that chemical
engineering is the discipline that is most strongly allied with biomedical
engineering. It is not a coincidence
that the Biomedical Engineering program at
Whereas we generally think of
electrical networks as carrying signals, within the body most signals are
carried through chemical reactions. Cells communicate with other cells by sending
messengers, as when platelet derived growth factor stimulates the proliferation
of smooth muscle cells to repair a damaged artery. The process proceeds by diffusion, which is a
slow process in engineering applications, but is a rapid process in the body
simply because the distances that must be traveled are miniscule. Even the transmission of nerve signals, which
we generally think of as electrical by nature, is in reality a chemical
phenomenon. Nerves release neural
transmitters, rather than electricity, to send messages to one another
We are used to thinking of
mechanical and chemical systems on the macroscale. Engineers build bridges and buildings and
petroleum processing plants.
Nonetheless, the body functions on the microscale. Cells are only a few microns in diameter, and
yet they respond to both chemical and mechanical stimuli. The single layer of cells that lines the
inside of an artery responds to the mechanical stimulation caused by the flow
of blood to maintain the correct diameter, and the individual cells within bone
respond to mechanical stress to maintain the bone’s strength. This active response is a unique aspect of
the body and one of the major challenges facing a biomedical engineer. While standard engineering materials do
change their properties in response to stress, the time scale is generally
longer than that of biological materials, and the changes generally represent a degradation, not an improvement in quality.