After this activity, students should be able to:

• Describe what happens when a blood vessel is blocked.
• Describe how bioengineering techniques can be used to "open up" a blocked blood vessel.
• Apply the engineering design process to create solutions to a problem.

In 2003, a 14 year old boy in China experienced severe chest pain during exercise. At the hospital, doctors found that he had a clogged artery, and if they were not able to clear it, he would go into cardiac arrest and experience heart failure. Luckily, the doctors were able to use an engineered stent to open his artery and prevent heart failure.

Do you know anyone who has had a heart attack? (Ask students to raise their hands.) Do you think that heart attacks are common? Why or why not? What causes them?

In a properly working human circulatory system, blood vessels are clean and smooth (like clean pipes). However, during the course of a lifetime, sometimes material coats the interior walls of blood vessels. This plaque, whether it hardens and stays in place, or hardens and gets dislodged, can have significant health consequences. Having material blocking the normal blood flow restricts the movement of blood, thus preventing sufficient nutrients and oxygen from reaching all parts of the body. Having plaque material moving though the blood vessels may also result in that material eventually encountering a smaller blood vessel and blocking any blood from going through, which prevents nutrients and oxygen from reaching everywhere they are needed. The problems this can cause are significant, problems such as heart attacks and strokes.

The best way to avoid these medical conditions is prevention via things like exercise and healthy eating. However, at the point when blockage is found, it must be treated to avoid health problems. Engineers and doctors have designed various ways to unclog or unblock a plaque-coated blood vessel. That's what we're going to look at today — heart attack and stroke treatment and prevention. How exactly is blood flow restored to the heart when plaque, or a blood clot, is blocking blood flow? Everyday biomedical, mechanical, chemical and electrical engineers work with medical doctors to devise more effective treatments for heart attacks and strokes. Today, we are going to see if we can do the same.

What ideas do you have about how we might unclog a blocked artery? (Listen to and encourage student brainstorming and ideas.) Currently, three primary treatments for clogged arteries are commonly in use (optional; show students the Three Methods to Treat Blocked Arteries attachment as either an overhead transparency or printout). The first two are types of angioplasty, or recreating of the canal in the blood vessel. The first method is a balloon catheter in which a small balloon is passed through the artery to the clogged area where it is inflated, compressing the plaque and opening the artery to greater flow. The second method is similar to the balloon catheter with the addition of a stent surrounding the balloon, so when the balloon inflates, the stent remains behind to keep the plaque pinned against the walls. The third method is a bypass surgery in which the blocked section of the artery is removed and the artery is reconnected, free of the blockage.

Before the Activity

• Gather materials and make copies of the Clearing Blocked Arteries Measurements Worksheet, one per person
• Make enough model blocked arteries to provide two per team. The representative artery/artery walls, made from either flexible rubber tubing or PVC pipe, are larger than the diameter of real human arteries, but serve as models for this open-ended design activity. To simulate the plaque buildup inside the model blocked arteries, use play dough or other material (such as peanut butter) that can be wedged inside but still soft enough to be moved about when students test their device designs (see Figure 1).

Figure 1. Example model blocked artery made from plastic tubing and play dough. click for copyright

With the Students: Design and Prototype

1. Divide the class into teams of three students each. Hand out the worksheets.
2. Demonstrate that blocked arteries have different flow than clear arteries by having the class time how long it takes for two liters of water to flow through a clear piece of piping at a 45° angle versus through a blocked piece of piping at the same angle (see Figure 2). Have students record these measurements on their worksheets.

Figure 2. Comparing flow through clogged and unclogged arteries. click for copyright

3. Explain the project to the student teams: Your challenge today is to create a device that could remove or flatten the built-up plaque material inside artery walls. How are you going to go about doing this? What are the steps a design team of engineers would take? (After students have suggested ideas, write on the board the steps all engineers go through in designing and solving problems. Understand the need, brainstorm ideas, design and plan, create and test a prototype, and review and improve.) Well, first engineers must have a problem or a need. Then, they brainstorm creative ideas and solutions to that problem or need. Next they select the most promising idea, and create a design that they can draw or communicate to others. They make a prototype of the design and test it to evaluate whether or not that design is successful.

click for copyright

4. Continue with the project instructions: Today, you and your team are engineers working together to create a device that could remove or flatten the built-up plaque material inside artery walls. Your team has two identical blocked arteries and a set of materials. Use the materials to develop a device to improve the flow in the artery. Remember, you do not have to use all of the materials. The last step of the design process is to review and improve on your design. You have two model arteries to built, test and then redesign with improvements. Keep in mind that you do not want to just knock the plague off the wall and leave it in the blood stream, and you do not want to hurt the fragile inside wall of the arteries.
5. Ask the students: What ideas do you have for how to unblock your model arteries? (As necessary, share the ideas that were mentioned during the Introduction/Motivation section of the activity, such as: dissolve the clot or blockage, use a balloon to push the artery open.)
6. Direct students to brainstorm, design (create a drawing with labeled materials), create a prototype and test their designs. The second design should be an improvement of the first.
7. Circulate among the groups as they work, ask questions as provided in the Assessment section. As students are working, challenge them to think about what happens to the plaque they dislodge, move or scrape away. We do not want the treatment to hurt the patient!

With the Students: Communication and Testing

With the Students: Conclusion and Reflection

Make sure students create feasible solutions, for example make sure their devices fit into their tubes and have a way of removing or flattening the plaque.

Make sure teams incorporate "lessons learned" from their first design/test as they create a revised and improved second design.

To make the model design more lifelike, have students create catheter device that could be used while water is flowing through the system.

Have students create engineering presentations that they would give to companies, hospitals or medical personnel highlighting the benefits of their particular medical devices.

See a good drawing of coronary Balloon Angioplasty at this National Institutes of Health website: http://www.nhlbi.nih.gov/health/dci/Diseases/Angioplasty/Angioplasty_howdone.html