The goal of our project is to develop a model mimicking valve functions that can be used to test the properties of aortic valves without using real specimens and using only materials available to us. We created a wooden apparatus to mimic the walls of the aorta with rubber flaps that interlocked to mimic the aortic valve. This allowed us to determine the amount of water flow similar to how a human heart valve would determine the amount of blood flow. While our model valve functioned, it was restricted in its ability to keep the flow consistent which may be due to human error in creating a valve as watertight as the real thing. To account for this error we made multiple redesigns and attempted a variety of tests; however, we were ultimately unable to solve this problem.

Background / Theory

The first step of our project was to use research to fully grasp what the heart is, what it does, and how it does it. We used padlets, a virtual dissection of the heart, sketches, and reports to understand the heart. Our next step was to think through how we would design our model by choosing our materials. Choosing materials was a crucial piece of the project because we needed to find materials that would have a close elasticity to the aortic valve in order to create a realistic prototype. Therefore, we tested our materials using Young’s modulus. Young's modulus is just a numerical value of this concept of elasticity. The stress on an object is based on a force applied to that object. The strain of an object is how much proportional change in length it experiences as a result of the force applied on it.

Governing Equations

Young’s modulus is found in the following equation:

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Purpose and Discovery Question

In our project, testing and using young’s modulus allowed us to determine what materials to use and in turn was the base of our design process. This led us to our question: how can we design and create a prototype that accurately mimics valves functions that can be used to test the properties of aortic valves without using real specimens and using only materials available to us?

Methods

Experiment Overview

We began with brainstorming how we would recreate an aortic valve with conventional materials. To start, we imagined a square tube with two rubber flaps, with a similar Young’s Modulus to a real heart valve, pressing against each other to stop water from coming through unless it was under high pressure.

With this concept in mind, we constructed the prototype.

After completing the design of our first prototype, we tested its functionality. We used water as ‘blood’ and opened and closed the valve to create the simulation of the valve relaxing and contracting. We attempted 3 tests each with small changes in the materials.

Core Prototype Picture

This was the core of our prototype. We used this base for all of the tests and alterations.

Procedures

We started our test by putting the prototype under a constant flow of water. Then, we opened and closed the ‘valve’ by pulling the wood pieces apart or pushing them together. By observing how much water came out of the bottom of the valve we could see if closing the ‘valve’ would create less water flow through the prototype.

Test 1

Overview

In our first test we started with a large black trash bag to keep our wooden “aorta” watertight. The water went through the top and to the rubber flaps. Then the rubber flaps would open and close based on how they were moved, allowing more or less water to go through.

Materials Table

Material

What it is used for/ How is it used

Wood

This provided the main structure for the valve to exist in and held its components in.

Rubber Tubing

We cut rubber tubing into the shape of aortic valve flaps in an attempt to mimic the real thing by keeping water out when the flaps were shut. This specific material was chosen because of its similarity in Young’s Modulus to that of a real heart.

Trash Bag

This kept the water contained inside the contraption so that the water would be funneled through the flaps and not around them.

Photo Evidence

Test 2

Overview

For our second test we used a balloon to aid the flaps in stopping water when necessary. We also used a smaller clear plastic bag in order to make our experiment more easily observable and attempt to contain more of the water inside of our contraption.

Materials Table

Material

What it is used for/ How it is used

Wood

This provided the main structure for the valve to exist in and held its components in.

Rubber Tubing

We cut rubber tubing into the shape of aortic valve flaps in an attempt to mimic the real thing by keeping water out when the flaps were shut. This specific material was chosen because of its similarity in Young’s Modulus to that of a real heart.

Small Plastic Bag

This kept the water contained inside the contraption so that the water would be funneled through the flaps and not around them.

Balloon

This provided an extra constrictive force on the water traveling through the valve to ensure that water would not move unwarranted.

Photo Evidence

Test 3

Overview

For our last test we continued to use the balloon, however, we cut the plastic bag shorter. We did this to attempt to prevent water from flowing to parts of the bag outside the contraption and make the experiment appear more streamlined and clean

Materials Table

Material

What it is used for/ How it is used

Wood

This provided the main structure for the valve to exist in and held its components in.

Rubber Tubing

We cut rubber tubing into the shape of aortic valve flaps in an attempt to mimic the real thing by keeping water out when the flaps were shut. This specific material was chosen because of its similarity in Young’s Modulus to that of a real heart.

Small plastic bag

This kept the water contained inside the contraption so that the water would be funneled through the flaps and not around them.

Balloon

This provided an extra constrictive force on the water traveling through the valve to ensure that water would not move unwarranted.

Photo Evidence

Results

Test 1

Video Evidence

https://drive.google.com/file/d/1W3mrsEX9vxcUZHDk7vGV8ONrJXXdUyiB/view?usp=sharing

Our first test proved that our prototype functioned properly. However we found that the big black trash bag was too wide to show clearly that the water was going where we wanted it to and when. Despite this, our prototype let less water flow through when the valve was closed and let more water flow through when the valve was opened.

Test 2

Video Evidence

https://drive.google.com/file/d/10jxQWELQiN1Aq047AzrMoj3LLWVuHKeZ/view?usp=sharing

For our second test we decided to change the bag we were using to make the results of our experiment more apparent by using a smaller clear plastic bag. We also added a balloon to the top of our ‘valve’ to add a small and flexible force to the water to prevent water from flowing at undesired times. Adding these materials to this test decreased the prototype's functionality. We believed this was due to the plastic bag being too long.

Test 3

Video Evidence

https://drive.google.com/file/d/1-5-db14Yci8reNdOk-0faNB-HvMbu-8e/view?usp=sharing

Our final test was similar to the second test. While we did cut down the plastic bag’s length quite a bit, the functionality of the prototype still decreased from the first trial.

Final Results

We can conclude from our tests that using a larger trash bag worked better to contain the water through the valve we created from rubber tubing. Ultimately we believe that if we used the materials from the first test, our prototype would work consistently.

Discussion

Discovery Question Resolution

In conclusion, we were able to design and create a prototype of a heart valve by using materials as simple as a few pieces of wood, a rubber tube, and a plastic bag. Figuring out how to build the model involved several stages of research followed by several stages of testing. We had to learn and demonstrate knowledge about the heart as well as Young’s modulus.

Theoretical Comparison

In researching online other methods of creating models of heart valves, we did not find any quite like ours. This could indicate several possibilities. One is that our style of heart valve model really does not work very well and so no one else is doing it. Another possibility is that most others just hadn’t tried our type of model before. Probably the most likely possibility is that our model can work, but there are other simpler models that do just as well.

Explanation of Anomalies/Errors

Despite us attempting to create a better functioning model, we can observe that our first test had the best outcome. We believe that the error in following trials was due to several factors. These factors may include a lack of a watertight chamber, which might have channeled more water through our valve, and the lack of a watertight valve, which would have fully stopped the flow of water when it was closed.

Conclusion

We were in fact able to create a decently functioning model of one part of the human heart, the aortic valve. Potentially more importantly, we learned about Young’s modulus and its applications in determining elasticity. This has the potential to be useful in our Capstone project, especially since we may be using materials such as silicone whose Young’s modulus we may want to test.

Future Work

We did not have as much time as we would have liked to complete this project, especially as we started focusing heavily on the capstone project to prepare for presentations to the STEM board. Thus, there are some things we would do better if we were to do it over again. One would be to do more trials so we could revise and improve the prototype more than we were able to. Additionally, we would measure the water going in and out of our prototype in order to take more accurate data, instead of mostly eyeballing it to make sure the water was doing what we wanted it to. This would allow us to more easily determine what needed to be improved and how those improvements could be made.