Students will discuss the special considerations that must be made when dealing with the human body, and will gain an appreciation for the amazing devices that have improved our quality of life. They will also explore how 'Form Fits Function'. This lesson should serve as a starting point for students to begin to ponder how the medical devices in their everyday lives actually work.

This lesson and associated activity look at the special design challenges engineers face when designing surgical instruments. Engineers must consider how to keep instruments sterile and reduce corrosion. biomedical engineering medicine materials biocompatibility Students will be able to make hypothesis about the function of an instrument from its shape and material properties. Students will be able to state some of the considerations that must be taken into account by biomedical engineers when working with the human body, which might not affect other engineering disciplines. Students will be able to hypothesize why a certain material was chosen for a specific medical instrument. Begin with a class discussion: What does the word "biomedical" mean? Why types of devices might an engineer design for a doctor, nurse, or surgeon? Do you think that a biomedical engineer has to think about different potential problems than a civil engineer? What other disciplines of engineering might influence biomedical engineering? Can you think of biomedical devices that involve electrical, mechanical, or computer engineering? Collect a set of random medical devices. These should be objects that the students will not be able to immediately identify. Ask the students to examine the devices and try to deduce their function by looking at the shape and composition of the devices. There is an incredibly wide range of biomedical devices that influence our lives and the lives of those around us. The design of biomedical instruments and devices involves concepts from every other discipline of engineering. Electrical Engineering - Electrical Engineering concepts provide a basis for a multitude of devices. They are helpful in biomedical engineering (BME) because they provide a means for studying biological signals. The body has its own electrical system that is used for communication through neurons, as well as in muscle contraction. An ECG, or electrocardiogram, is used to monitor the electrical signals generated by the beating of the heart. An ECG can be used to determine whether the heart signal is normal, and if it is not normal whether or not there is a danger. An EEG, or electroencephalogram, is a similar device that can display the electrical signals generated by the brain. Both ECG and EEG are primarily diagnostic tools, but there are also therapeutic devices that are electrical in nature. Devices such as pacemakers and defibrillators rely heavily on electrical engineering. A pacemaker provides a pulse of electrical current to stimulate the heart when it is not beating regularly. A defibrillator applies a much larger current to jumpstart the heart when it has stopped beating all together. Students may be familiar with some of these devices through their families, or even TV shows or movies. Mechanical Engineering - Many other devices and instruments are mechanical in nature, and require biomedical engineers to have a fundamental understanding of the forces acting on objects in different situations. Many surgical instruments are purely mechanical, and so are most prosthetics and many implants. A prosthetic leg must be engineered to perform in all types of situations (i.e. walking, running, sitting), and still be aesthetically acceptable. Artificial joints have been created that can totally replace an entire knee or hip. A hip implant is a made of a ball and socket, just like our healthy hips. A knee replacement is very different due to the very different range of motion of the knee. It moves in only one plane. Other mechanical devices that have changed the lives of many people are artificial heart valves and catheter delivery systems. Computer Science - With many biomedical devices, precision is key. Instead of manual operation, many devices are automated with the use of computer programs. That way, even those of us with shaky hands could be capable of performing delicate tasks. Computers are also of extreme importance in the design process. When a new device is designed, it is first tested in computer models before it is used on animals or people. Computer programs are also used in conjunction with electrical devices to interpret the electrical signals that are received. For example, a computer can be used to determine whether the output of an ECG is irregular, and if so, determine what kind of problem exists. Imaging - Advances in imaging systems have allowed us to learn a great deal about our physiology, and have helped us find solutions to many medical problems. The most common imaging technique is the well-known X-ray. Another option is computerized tomography, or CT. A CT image is created by taking many two dimensional X-rays and building them into a three dimensional image. A third well-known imaging modality is magnetic resonance imaging, or MRI. MRI uses a magnetic field and a radio signal to create images of the body's interior. Its advantage is that unlike X-ray and CT, it does not involve any harmful ionizing radiation. Chemical Engineering - Chemical engineering concepts are also crucial to biomedical engineering. It is necessary to determine how devices and implants will interact chemically with the body. We must be sure that a specific material is not harmful or toxic before placing it inside an animal or human. Chemical engineering is also important in the field of drug delivery. Engineers are capable of creating polymers (a group of materials that includes plastics and rubbers) that can be used to carry drugs. These materials can be implanted in the body, and will release the drug at a predictable rate. There are many special considerations that a biomedical engineer must make, that a civil or mechanical engineer may not have to worry about. Minimally Invasive - A biomedical engineer will strive to make any procedure minimally invasive. This means that a procedure will have the smallest incision possible to still meet the required goal. The biomedical engineer tries to design instruments that will maximize the comfort of the patient, and reduce the chance of infection. Biocompatibility - Any materials that are used must not cause any adverse biological reactions. If the materials are not biocompatible, the body will reject them, causing inflammation and swelling. Lightweight - If a material is being used for an implant or prosthetic, it must be relatively light weight. A prosthetic limb made out of concrete, no matter how well designed, could never be practical. Corrosion Resistant - Much of the body is made up of water. Any implanted material must be able to stay in this wet environment without oxidizing, or rusting. Corrosion would cause inflammation, which is likely to reduce the performance of the device and be uncomfortable for the patient. Little Debris - Certain implants and prosthetics need to move within the body. An engineer must make sure that there are no materials rubbing against each other that might create particles of debris. Debris, like corrosion, causes unnecessary inflammation. For instance, a knee replacement moves inside the body at the knee joint. It is important that no debris is created from the rubbing of the upper and lower joint surfaces. Long Lifetime - An engineer should strive to design products that will last as long as necessary. For example, a pacemaker would be of little use if the batteries needed to be changed every month. Electrical Safety - When a patient is connected to electrical biomedical devices, it is important that a patient is not connected directly to a power line. It is important that circuitry includes safety devices so that dangerous levels of electrical current do not flow through the body under any circumstances. Bioethics - A biomedical engineer will often need to test designs. After computer modeling, this is usually performed on animals, and then human test groups. An engineer must always be respectful and conscientious of the lives that they affect. He or she must always consider every possible problem before risking the lives of other people. Since most medical instruments are designed for a specific purpose, it is important that their form fit the intended function. Here are a few examples: Vascular Grafts - Vascular grafts are devices that can be used to replace vascular tissue, like major arteries and veins. These are flexible, stretchy tubes composed of a synthetic cloth material called Dacron, or a plastic-type material called polytetraflouroethylene, otherwise known as Teflon. These grafts can be sewn to the end or side of another artery or vein to bypass a damaged or blocked vessel. [Interesting fact: Teflon is the same material that is often used as the non-stick coating on frying pans. The purpose is exactly the same. Blood should not stick to the vascular graft. If blood does stick and begins to clot, the condition is called thrombosis and can be very dangerous. All vascular devices should be designed to reduce the risk of thrombosis.] Laparoscopy - Laparoscopic surgery is a type of minimally invasive surgery. A small incision is made in the abdomen, and the entire abdominal cavity is inflated with carbon dioxide. Two or three other holes, or ports, are made, and surgery is performed using specialized tools that are inserted through these ports. The instruments used in these kinds of procedures are very narrow so that they can fit through the ports. They are also fairly long so that the handle of the instrument can be outside of the body, while the other end is inside of the body. The ends of these instruments are specially designed for a multitude of uses. They can cut, grasp, clamp, and staple, just to name a few uses. How does the surgeon see what he or she is doing? A special camera called a laparoscope is also inserted through one of the ports. It has a light source and lens on the end that is inserted into the body. Fiber optics in the scope act as light pipes to send light into the body and carry the image out to a television screen. Like the other laparoscopic instruments, the laparoscope is long and thin in order to fit its function. Hip Replacement - A healthy hip is a ball and socket joint that allows for motion in many directions. A hip implant looks very similar. It is composed of a titanium post with a ball on the end. The post is inserted into the femur. The top portion of the implant is called the acetabular cup. It is a cup shaped piece of metal, usually cobalt chromium, that fits over the ball. This cup is implanted into the acetabulum, which is a part of the pelvis. Both titanium and cobalt chromium are extremely strong, light weight, corrosion resistant, and biocompatible. The inside of the cup is lined with smooth plastic so that the ball can easily swivel inside without creating any debris particles. One interesting fact about these types of implants is that the metal parts are often covered in tiny bumps or ridges. The bumps allow for bone to grow into the spaces, so that the implant is held tightly by normal bone tissue. imaging technique that uses invisible electromagnetic radiation to create images of the inside of the body. An imaging technique that creates a three-dimensional image from many two-dimensional X-ray images. When a metal deteriorates by chemical reaction, often in response to moisture. For iron, this is known as rusting. Surgery that allows surgeons to perform procedures without making major incisions that can lead to long recovery times. When a material is suitable for use inside the body. There is little chance for adverse reactions to occur. A form of minimally invasive surgery that allows surgeons to perform procedures without making major incisions that can lead to long recovery times. A tubular prosthetic that helps maintain proper blood flow by replacing or bypassing a damaged artery or vein. Thin tubes, usually made of glass or plastic, which can transmit light from one location to another. Surgical Resident for a Day In groups or pairs, students can be asked to think of a biomedical device (real or imagined). They should then draw multiple views of the device to present to the class. They should also state how the form of the device fits its function, as well as what materials it might be made of. Ask students to list several special considerations that a biomedical engineer must make when designing a device. Students can be asked to describe ways in which other disciplines of engineering are used by biomedical engineers. For instance, a biomedical engineering device can be presented to the students, and they can be asked to describe which other engineering disciplines were used in the development of the device and why. Have a speaker come in and talk about their own personal experiences using a biomedical device. This might be a person using a prosthetic limb or a pacemaker. Ask students to keep a journal of all of the biomedical devices that they come in contact with for two weeks. Examples of laparoscopic surgery and more information about available procedures may be found at http://www.laparoscopy.com/