Lesson: Blood Clots, Polymers and StrokesContributed by: Science and Engineering of the Environment of Los Angeles (SEE-LA) GK-12 Program, UCLA
Educational Standards :
Learning Objectives (Return to Contents)
After this lesson, students should be able to:
Introduction/Motivation (Return to Contents)
Engineering and the medical field are very different career paths… or are they? You might be surprised to hear that one field of engineering is called biomedical engineering. Biomedical engineers develop new technologies, devices and procedures that doctors and surgeons use to help patients. To design effective and safe technologies, biomedical engineers must have a well-developed understanding of the human body and its systems, from biological, chemical and physical perspectives.
We are going to conduct an activity in which you work as biomedical engineers to develop a solution for a problem related to the circulatory system. Before we start the activity, let's make sure we fully understand the problem. To do that, we are going to learn all about strokes, blood clots and polymers. The relationships between these three topics involve biological, chemical and physical science! We will learn how these three realms of scientific knowledge help us to understand the causes and effects of strokes, as well as how biomedical engineers invent creative chemical and mechanical solutions to protect the health of patients at risk for strokes.
Lesson Background & Concepts for Teachers (Return to Contents)
(Have available a computer with internet access and a projector to show students the 10-slide Blood Clots, Polymers and Strokes Presentation along with the information below, as well as a showing them the 3-D animation and short videos listed in the Additional Multimedia Support section that are helpful in teaching this material. The slides are "animated," so clicking the mouse or space bar brings up the next item. Also, having a real brain for students to see and touch, or a classroom model, is helpful.)
Strokes and the Brain
Every year, approximately 800,000 people experience strokes, the leading cause of adult-onset disability in the U.S. A stroke, also called a brain attack, is a loss of brain function due to an interruption of blood supply to the brain. Lack of adequate blood supply or ischemia, starves the affected region of the brain of nutrients and can cause it to die. The human brain has more than 100 billion neurons and different functions are localized in different regions of the brain. Despite the large number of neurons, the slightest loss of brain tissue can result in catastrophic disabilities.
Different regions of the brain have different functions; therefore, the effects of a stroke are dependent upon its location and severity, that is, how much tissue is deprived of blood and for how long. The major regions of the brain are the cerebrum, cerebellum and brain stem. The consequences of strokes are different for each region (see Table 1). As a general rule, strokes occurring in the left hemisphere of the brain affect the left side of the face and the right side of the body. Likewise, strokes occurring in the right hemisphere affect the right side of the face and the left side of the body.
In each region of the brain, localized areas are responsible for particular functions. For example Broca's area and Wernicke's area, located on the left side of the cerebrum (see Figure 1), control speech and language comprehension, respectively. A stroke occurring in Broca's area leaves a person with an impaired ability to speak, while not affecting his/her language comprehension.
Have ready some resources to inform students about the various regions of the brain (see website URLs in the Additional Multimedia Support section), such as:
Using whatever resources are available, point out the different regions of the brain and their corresponding functions. What would occur if certain portions of the brain atrophied? How difficult it would be to go through life lacking these functions and dependent on others?
Ischemic stroke can occur due to a blood vessel blockage as a result of a formed blood clot (thrombosis), or a blood clot or plaque that migrated to block blood flow (embolism). Stroke can also be due to hemorrhage, called hemorrhagic stroke, which is when a weakened blood vessel ruptures and bleeds. Hemorrhages cause blood to accumulate in surrounding brain tissue, causing damage and compression. Ischemic stroke is far more common, causing 87% of all strokes.
A polymer is a large molecule composed of repeating units covalently bonded to one another. The repeating units are termed monomers, which are composed of collections of atoms. Polymerization is the process of covalently linking together monomers to form long chain polymers, with carbon, oxygen, nitrogen, and silicone commonly found in the backbone. The monomer structure and its connectivity in making the polymer determine the overall polymer properties. Also, separate polymer chains can bind to one another through connections known as cross-links. Cross-links hold polymers together, reducing the ability for polymers to slide past one another, effectively altering their physical properties.
Polymers can be naturally or synthetically created. Synthetic polymers are diverse and widespread, and include nylon, polystyrene and Teflon. In humans, polymers are paramount for life processes; examples include polysaccharides (polymers of sugars), polypeptides (polymers of amino acids), and polynucleic acids (polymers of nucleic acids).
Blood is a fluid composed of plasma, blood cells, platelets, and a variety of dissolved proteins, sugars and minerals. For every cell in the body, blood is essential for the delivery of nutrients and removal of waste. Blood is confined to the blood vessels of the body, pushed through the system by the heart. Loss of blood, even through a small cut, can lead to death if not healed or treated. Blood clots form at the sites of damaged blood vessels in order to stop bleeding.
The process of forming a blood clot is called coagulation. (Show students a two-minute video on how blood clots; see website URL provided in the Additional Multimedia Support section.) Damage to a blood vessel is sensed by platelets, which immediately begin to bind to the damaged tissue and plug the opening. The damage is also sensed by protein molecules floating by in the blood, called clotting or coagulation factors. Through a complex cascade of reactions involving dozens of molecules and proteins, fibrinogen, an important blood-clotting protein, is recruited to the damage site and converted to fibrin. Fibrin then polymerizes to form a meshwork in conjunction with the platelets to form a blood clot. Abnormalities in this process can lead to severe complications; excessive clotting can result in heart attack and stroke, whereas less effective clotting can result in hemorrhage.
Biomedical Engineering Inventions
Generally, stroke treatment consists of a variety of drugs designed to thin the blood and break-down clots, with the end goal to restore blood flow to the ischemic area. Sometimes, clots do not respond to these treatments, and must be physically removed. In response to this need, biomedical engineers have created minimally invasive, catheter-based tools that are inserted into arteries to travel to the blockage sites where they remove or destroy blood clots in order to restore blood flow to the region.
Examples: FDA-approved in 2004, the Merci Retrieval System is a small, long and narrow, corkscrew-shaped device that is fed into the femoral artery in the groin area and navigates to the brain blockage site where it grabs the clot, and slowly pulls it back through the vessels and out of the body. The Penumbra System is designed to "suck up" the clot and remove it from the body. (Show photos and/or short animation videos on both of these devices; see website URLs provided in the Additional Multimedia Support section). Figure 2 shows another example, the Insera SHELTER device.
Vocabulary/Definitions (Return to Contents)
Associated Activities (Return to Contents)
Lesson Closure (Return to Contents)
Biomedical engineers who focus on issues related to the circulatory system, blood clots and strokes must conduct extensive research about these topics. They must understand how the circulatory system operates, how blood clots are formed and how they function, as well as understanding all the causes and effects of different strokes. Just like biomedical engineers, we have learned a lot of new information about all these topics. Now we are ready to apply this information! In our upcoming activity, we apply our knowledge to design a way to break down a potentially life-threatening blood clot.
Attachments (Return to Contents)
Assessment (Return to Contents)
Brainstorming: Ask students to brainstorm any type of disease or health issue that could be helped through engineering. Have them list their ideas, along with how they think engineering could help. Ask each student to share at least one idea with the class and record the ideas on the board.
Lesson Summary Assessment
Show What You Know! Have students complete the Blood Clots, Polymers and Strokes Worksheet as an assessment of what they learned during the lesson. Worksheet questions cover polymers, blood clots, different types of strokes and vocabulary words. Collect the completed worksheets at lesson end, once the presentation is finished, to gauge student comprehension of the information presented.
Additional Multimedia Support (Return to Contents)
An interactive "3-D brain" visual aid provides moveable illustrations of brain regions and information on functions at the Genes to Cognition Online website at: http://www.g2conline.org/ (select "3-D Brain" from the top right side, then on the left side, choose the portion of the brain to view; use the far right controls to move the images and turn on/off descriptive labels).
Stroke: An Animation, a 2.5-minute video explains how a stroke happens and different types of strokes. See the National Health Service (UK) website: http://www.nhs.uk/Video/Pages/Strokeanimation.aspx?searchtype=Search&searchterm=stroke&offset=1&.
Stroke Animation Video (41 seconds) shows what happens to the brain during a stroke, on YouTube at: ( http://www.youtube.com/watch?v=M_fo6ytlmD0).
How Does Blood Clot video (2:01 minutes) explains how blood clots and why it is important, on YouTube at: http://www.youtube.com/watch?v=--bZUeb83uU.
Photo of the Merci Retrieval System and Penumbra System, devices created by biomedical engineers to remove blood clots in human blood vessels, at the Annals of Internal Medicine, February 15, 2011, Vol. 154, No. 4: https://annals.org/article.aspx?articleid=746808
Merci Retrieval System X Series Animation (2:14 minutes) shows how this blood clot removal tool works, on YouTube at: http://www.youtube.com/watch?v=99x_APzvD1c.
Penumbra for Stroke (1:23 minutes) shows how this blood clot removal device works, on YouTube at: http://www.youtube.com/watch?v=_-irwhRes90
References (Return to Contents)
Chemistry. Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. Accessed May 3, 2009 http://www.britannica.com/EBchecked/topic/108987/chemistry
Heart Disease and Stroke Statistics. 2009 Update: A Report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. 2009. Accessed May 3, 2009 http://circ.ahajournals.org/cgi/reprint/CIRCULATIONAHA.108.191261
Types of Stroke. Ohio State University Medical Center. Accessed January 22, 2013. http://medicalcenter.osu.edu/patientcare/healthcare_services/stroke/types/Pages/index.aspx
ContributorsAzim Laiwalla, Ann McCabe, Carleigh Samson, Victoria Lanaghan
Supporting Program (Return to Contents)Science and Engineering of the Environment of Los Angeles (SEE-LA) GK-12 Program, UCLA
Acknowledgements (Return to Contents)
This digital library content was developed by the University of California's SEE-LA GK-12 program under National Science Foundation grant number DGE-0742410. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.