1128 DHS RoboTEx Artificial Heart - BESTRobotics2023

Contact Name:  Jayden Lin ([email protected])

School: W. P. Davidson High School (RoboTEx - Team 1128)

BEST Hub: Emerald Coast BEST

Introduction

Figure 1: 3D printed prototype.

The function of the human heart within the body serves two main functions. The first is to push deoxygenated blood from the superior and inferior vena cavae into the pulmonary artery in order to be reoxygenated with blood. The second is to take the oxygenated blood from the pulmonary vein and push it through the aorta. In doing these functions, the human heart is able to provide ample oxygen to the rest of the body. 

To do this, the heart is divided into four different sections: the right and left atria and the right and left ventricles. The deoxygenated blood from the vena cavae first enters the heart through the right atrium. After passing through the tricuspid valve(the valves are to prevent accidental backflow), the blood flows into the right ventricle. The right ventricle then pumps the blood through the pulmonary valve into the pulmonary artery that leads to the lungs. After this, the same mechanism occurs on the left side of the heart. The oxygenated blood enters the left atrium from the pulmonary veins and passes through the bicuspid valve into the left ventricle, and the left ventricle pumps the blood through the aortic valve to the rest of the body.

Design Process

Analysis

The team was tasked with the challenge of creating a “bridge to transplant” using 3D printing technologies. Heart transplants are needed due to different medical issues such as cardiomyopathy, coronary artery diseases, heart valve diseases, ventricular arrhythmias, congenital heart defects, or a variety of other issues. However, an issue arises during the time gap between keeping a patient with heart failure alive and a donor becoming available. This issue is where the “bridge to transplant” arises, as it is able to keep the patient alive during this critical time period.

Research

After discussing the function of the heart as discussed in the introduction, the team determined to create a system that would mechanically cause both influx and outflow of blood while preventing backflow. The team determined that it would need to create at least two chambers in order to ensure that the oxygenated and deoxygenated blood would not mix. However, the team wanted to create a system driven by only one motor in order to be as minimally invasive as possible.

Brainstorming and Planning

In order to create such a device, the team analyzed different design possibilities. The first item determined by the team to be used was the use of a check valve. Check valves function by allowing fluid to pass through in the forward direction while preventing backflow by closing for the backward direction. This would serve to recreate the bicuspid, tricuspid, pulmonary, and aortic valves, and prevent potential accidental backflow of fluid that could potentially cause the mixing of deoxygenated and oxygenated blood. Additionally, a piston design was implemented to push the fluid throughout the body. These designs essentially worked in mimicking a positive displacement pump design. Positive displacement pumps work by controlling the expansion and shrinking of volume with a piston, and use check valves in order to ensure the flow of liquid is only in one direction. The other option was to use a centrifugal pump, which works through centrifugal forces by using an impeller in order to move liquid in one direction. However, to maintain the same conditions of the Windkessel effect (expansion and shrinkage of blood vessels) on endothelium throughout the body, and to ensure the least change in the homeostasis of these cells, a positive displacement pump design was determined to be more effective. Additionally, it was decided that there would be two separate chambers to simulate the right and left atria and ventricles in order to prevent the accidental mixing of blood. A piston would be split into two prongs in order to power the system with one motor from the same location. Finally, in order to ensure the stretching of the blood vessels in order to connect with the artificial heart was minimal, a classic heart shape design was chosen due to its similarity to the placement of the different vessels (Vena Cava, Aorta, Pulmonary Artery, and Pulmonary Veins). This design is meant to be scaleable in order to fit the 5-inch by 3.5-inch average size of a human heart, in order to make it as minimally invasive for the body as possible.

Figure 2: Diagram of a Check Valve.

Figures 3 and 4: Similarities between positions of vessels.

Figure 5: Notes on Pump Concepts.

Design Summary(SolidWorks)

The design utilizes four separate check valves for each chamber of the artificial heart. These valves are designed using a hinge and a dropdown flap that prevents the backflow of fluid. There are additional smaller chambers placed in order to ensure that the movement of the valves to allow and prevent fluid into the lungs does not interfere with the blood vessels. Additionally, the piston in the design uses a 2-pronged design in order to provide the volume displacement for both the left and right chambers. Finally, holes were cut at the top of the design to allow for a place for the vessels to attach.

Future Studies

A few things could be done to improve upon the design in order to make it more physiological and viable for a “bridge to transplant”. One thing that could be done would be to increase the size of the piston on the left ventricle. This would better stimulate the increased volume required to be pushed by the left ventricle as the left ventricle pumps blood to the entire body whereas the right ventricle simply pumps blood to the lungs. However, this was not implemented due to the prototype nature of the device but would be implemented after determining the viability of the device. Another thing that could be done would be the creation of a full piston system to create a place for a motor to attach. This would allow for a compact way to allow a motor to be attached, which would pull and push the piston mechanically rather than manually as in testing.

Design Explanations

Figure 6: As the piston pulls back, it opens the check valve which allows the flow of blood into the chamber.

Figure 7: As the piston pushes forward, it closes those check valves and opens the other two check valves to push blood out of the heart.

Figure 8: Arrows showing the direction of blood flow.

Print Specifications

Printer Used: Monoprice Select Mini V1

Infill Percentage: 50 Percent

Brim: NO

Supports: YES

Type of Filament: PLA