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.