Design An Aortic Heart Valve Model

Challenge Problem:

"You are a team of engineers for a bio-materials company that has a cardiovascular systems client who wants you to develop a model that can be used to test the properties of heart valves without using real specimens."

The next step in Part 1, was to watch a virtual heart dissection and record what I learned in my engineering notebook. After I took these notes, I then sketched the outside and cross-section (inside) views of the human heart. Both my notes and sketches can be seen below!

Design A Heart Valve Model: Part 2

In part 2, the main goal for my team was to understand Elasticity and Young's Modulus for our tissue analysis. At this point in the activity, my group undertstood how the heart functioned as a whole but it was now time to dive deeper into specifically the aortic valve's functionality.

The next step was to use our research to help complete a series of practice problems revolving around Young's Modulus. The work to some of the practice problems and the table/graph we made for Question 2 can be seen below. These practice problems strengthened our skills at being able to calculate the Young's Modulus of a material, which we were required to find when testing our own materials.

Design A Heart Valve Model: Part 3

Now that my team has a solid foundation of the heart's blood flow, structure, and valve structure, we began to start designing our heart valve model.

The first step of Part 3 was to pick materials that we wanted to test to see if they would work well in our heart valve model. The goal of this testing process was to find materials that mimic the elasticity and physical componets as those seen in a real aortic heart valve. Throughout the testing process, we were always considering the trilaminar structure of aortic valves, meaning the three layers of the aortic valve leafets (specifically the ventricularis and fibrosa layers in the leafet).

We ended up choosing four materials to test. A light resistance band, a heavy resistance band, a balloon, and a long resistance band. (materials seen below - left image)

To test the materials we set up an elasticty-testing station (seen above - right image). We ran a elasticity test for each of our four materials and were able to determine each materials Young's Modulus. We also created a Stress v Strain graph for each material. Pictures of us testing our materials can be seen below!

The next step was to officially begin designing and building our prototype! Our heart valve model needed to be thin like an aortic valve, be made up of at least two layers, one of these layers needed to be more elastic than the other, and the model needed to recoil back to "open position" after force was removed from it.

Before we began to build our prototype we brainstormed. In the brainstorming process each group member sketched ideas of what we wanted our heart valve model to look like and how it would function. Three of my sketches can be seen below.

We decided to test one of my teammates sketches first. This idea was to have two elastic bands running through the center of a water bottle. Each band would have a small hole cut in the center of the band. When force was exerted, the bands would be stretched outwards in both directions away from the water bottle. As the bands stretched, the hole in the center would become smaller and smaller until it disappeared. When force was released the two bands would naturally recoil back to "open position". Images of my group testing this idea can be seen below.

Unfortunately this idea did not work. Since the band was a rectangular shape going through a cylinder, water leaked around the side. The hole would close but too much force would displace the band and cause more leakage. However, our group was not phased and was inspired to try out a new idea!

The next idea we tested can be seen in my "sketch 3" picture. The idea for this design was that it would have to elastic bands making a cone shape. When no force was being exerted onto the layers, a hole would remain at the to bottom, where "blood" could easily flow through. When force was exerted on the bottom of the bands, they were pulled downward and caused the hole to shrink then close. When this downward force removed, the bands would immediately recoil and return back to "open position".

Pictures of our new functioning heart valve can be seen below!

Now that we had our functioning heart valve model, I was able to draw up a final sketch of our model which can be seen below (left). Each team was responsible for writing up one more lab report for this project which can also be seen below (right). In the lab report we included detailed steps about our brainstorming process, all of our team sketches, our testing methods, our final model, and our lab analysis.

Content

• Aortic Valve: The main outflow valve for the left heart. It is the valve between the heart and the body. The aortic valve opens when the left ventricle squeezes to pump out blood, and closes in between heart beats to keep blood from going backward into the heart.

• Aorta: The aorta is the main artery in the heart. It carries blood away from your heart to the rest of your body. The blood leaves the heart through the aortic valve. Blood then travels through the aorta, making a cane-shaped curve that allows other major arteries to deliver oxygen-rich blood to the brain, muscles and other cells.

• The cross-sectional area: the area of a two-dimensional shape that is obtained when a three-dimensional object. For example a cylinder is sliced perpendicular to some specified axis at a point. For example, the cross-section of a cylinder - when sliced parallel to its base - is a circle.

• Ventricles: A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The atrium (an adjacent/upper heart chamber that is smaller than a ventricle) primes the pump.

• Atriums: The two atria are thin-walled chambers that receive blood from the veins. The two ventricles are thick-walled chambers that forcefully pump blood out of the heart. The right atrium receives deoxygenated blood from systemic veins; the left atrium receives oxygenated blood from the pulmonary veins.

• Young Modulus: The Young's modulus (E) is a property of the material that tells us how easily it can stretch and deform and is defined as the ratio of tensile stress (σ) to tensile strain (ε).

• Elasticity: elasticity is the ability of a deformable body(e.g., steel, aluminum, rubber, wood, crystals, etc.) to resist a distorting effect and to return to its original size and shape when that influence or force is removed.

• Kilopascal (kPa): one thousand times the unit of pressure and stress in the metre-kilogram-second system (the International System of Units [SI]). One pascal is a pressure of one newton per square metre, or, in SI base units, one kilogram per metre per second squared.

Reflection

This was an amazing project, as it allowed me to explore out my comfort zone and strengthen my time management skills. Before this class I was no expert on the heart or it's functionality. I knew the basics but not nearly as much as I know now. Trying to design a model to mimic something you have little knowledge about is a little scary at first. However, I spent a lot of time researching inside and outside of class to really take the time to master the functionality of the heart. I became a benifial teammate as I used my knowledge gained to help teach my teammates when they were confused. I was proud of myself for being able to perform well and write two full lab reports on a subject I had almost no backround knowledge on coming into this project.

This project included a lot of work with a lot of steps, maing it was extremely to always get everything done on time. Otherwise I could easily fall so far behind that it would be nearly impossible to catch up. I made it my goal to stay organized throughout this project. I was always on top of my work and never wasted a singular minute of class time. This was great as I never had a late assignment and I was able to help my teammates complete their work if they appeared to be falling behind. This project greatly increased my confidence, as I learned that I can do anything successfully if I put in the extra work. I look forward to my future in this class as I learn new topics, explore my creativity through sketching, and improve my writing skills through lab reports.