Optimal Designs. A System to Quantify Heart Valve Leaflet Strain

Transcription

1 1 Optimal Designs A System to Quantify Heart Valve Leaflet Strain Team #10 Team Members: Michael Napolitano, Andrea Mandragouras, Victoria Fernandez Project for Client: Dr. Wei Sun Client Contact Dr. Wei Sun Biomedical Engineering Program at Uconn, Arthur B. Bronwell Building Rm. 203 Phone: (860) Fax: (860) weisun@engr.uconn.edu

2 2 1. Introduction The purpose of this project is to design a strain measuring system which has the ability to obtain and measure how a bioprosthetic and transcatheter valves are affected under specific applied pressures. This project is important because the testers working with these valves have to be able to see whether or not these heart valves are suitable and can continue further testing on them. Some of the other tests are extremely time consuming and this will tell them whether those tests are worth the time and hassle. The general setup for this device is to have two different containers that are attached by precise tubing. In the first cylinder it will be used to hold the water which will eventually be transferred over to the second cylinder, through designed tubing, where the heart valves will be held. The closing of the three valve leaflets will be caused when the pressure is being applied by the mechanical pump which will be connected to the first container. The mechanical pump is used so the desired pressure, which will be between 40 mmhg to 200 mmhg, can be accurately reached. The second cylinder will be smaller and wider than the first tube and here is where the heart valve will be housed. The reason that this cylinder is smaller than the first one is to make it easy for the valve tester to see how the valve is reacting when the pressure is being added to the system. This device is designed in a special valve leaflet testing system which the tester will be able to analyze all three of the valve leaflets separately. Each of the valve leaflets will then be broken up to six subsections which will give the testers the ability to precisely analyzing every part of each leaflet so it can be shown if an abnormality is occurring. This will be made possible to test the three leaflets separately and accurately because the valve will be placed into a rotating holder. Also, in the second container there will be two high speed cameras with boroscopic lenses in order to get an up-close accurate view of how the valves react when the strain is applied to the system. Attached to the cameras is a program called Xcap which is used to store and adjust the pictures that are being taken by the two cameras. From here, this is where the Labview is connected to. This Labview program will be able to take the pictures that the camera has taken and turn them into 3D. Then using a Labview program created the user will be able to evaluate the pictures to make sure the valves are suitable to be used. In order to examine these valves there is a pressure sensor attached in the second cylinder. The purpose of this pressure sensor is to make sure that an accurate pressure in the system is being reached. Also, attached to the pressure sensor is DataTrax. The main problem that we will encounter in the design is making sure that the appropriate pressure can be reached. This will be made possible because of the use of dragon skin. Dragon skin will be used around both of the cameras in order to hold the desired pressure in the testing tube. Coming from underneath the valve being tested there is another small tube which will be used to allow the water leakage to go through the heart valve. The water that is allowed to leak through the heart valves and this small tubing will be directly connected to a collecting jar. This collecting jar is very important for this design because it is important for the user to be able to see the amount of leakage that is going through the valve. This amount of water will then be able to be measured by the user. If there is too much leakage occurring it shows that

3 3 there is a problem with that specific valve and also it is a problem if not enough water is leaking through the system. The two different cylinders will be connected by a designed tube which will be made to both open and close for the user. When the test is in progress this tube will be open so that both the water and the pressure can be transferred from the first cylinder to the second. It is imperative that very minimal to zero leakage is occurring from this tube. 1.2 Subunits Figure 1: Solidworks design of the system Holding Chamber The first component of the design is the holding chamber, a cylindrical chamber made of Plexiglas. This chamber will hold and supply the saline solution from a prepare solution source into the testing chamber. The saline solution will maintained at a temperature of 37 degrees Celsius to simulate a more realistic environment relative to the human body. To keep a compressed pressure with Bumper bolts and nuts with low dome stainless steel caps will be used to keep the chamber secured. To avoid any leakage in the holding chamber silicone molding will be added along the diameter of the necessary holes where bolts and nuts will be secured to the top and bottom of the cylinder. The top and bottom of the cylinder will be squares will have rings detentions that fit into cylinder. Plastic tubing will connect the holding chamber at the

4 4 bottom of the cylinder to the top of the testing chamber. The holes that connect to the plastic tubing of the holding chamber will also be secured with silicone along their diameter to prevent saline solution leakage. The holding tank will have two holes, one for pump and the other for the hose. The chamber will be able to hold pressure but importantly a steady pressure to plus or minus 5 mmhg. Once the chamber is secured and sealed it will maintain a desired pressure for testing which will range from 40 mmhg to 200 mmhg. It is very important to make sure the holding chamber and testing maintain equal pressure. In addition, the holding chamber will have a width of 6 inches and height of 12 inches making it tall and wide so it can sustain large volumes of solution. A wooden platform will be supporting the holding chamber at a height higher above the testing chamber. The sole purpose of the holding chamber is to hold the saline solution for the testing chamber. Figure 2: Holding Tank Testing Chamber The next component of the design is the testing chamber where the mounted heart valve will be housed. This tank will also be a cylinder made of Plexiglas however this tank will be short and wide that will allow for easy view for the human eye of the heart valve as it being tested. Therefore, the testing chamber will have a width of 6 inches and height of 8 inches. The inside of the Plexiglas container will be coated with a special spray that will clear up the condensation produced by the water temperature. A top view and bottom view of the heart valve is desired at all times because it is important for the human eye to see the leaflets as close as possible. Another significant factor that needs to be eliminated in order to maintain a good view of the heart valve is a nozzle. The nozzle will be attached to the testing chamber to remove any air bubbles that may be trapped at the top of the chamber. Connected to the nozzle will be QOSINA s High Pressure Stopcocks will be open and closed at any time while allowing air bubbles to be removed from the system (Figure 1). Since there will be water leakage through the

5 5 valve the pump must be able to counteract the pressure drop as best as possible. This will help maintain an accurate pressure reading. Connected to hose and pump will be barb connectors eliminate water leakage and maintain the system secured at the desired pressure. Figure 3: QOSINA s High Pressure Stopcocks Similarly to the holding chamber set up, a wooden platform will be supporting the testing chamber but at height below the holding chamber. On top of the testing chamber will be a hole where the saline solution will be coming from the holding chamber. Additionally, another hole will be located at the same level as the mounted heart valve that will connect to the pressure transducer. In order to calibrate the cameras, a hole will be made where the calibration cube will be mounted in the system. Below the testing chamber, the platform of the mounted valve will have a hole that will allow water to leak through. Figure 4: CAD design of testing chamber.

6 6 Figure 5: Testing Chamber Mechanical Pump The system, which consisting of the holding and testing chamber must maintain an overall pressure. In order to maintain an accurate digital reading of the pressure inside of the system a mechanical pump will be used. The accuracy will be greater than with a hand pump because the mechanical pump will have a digital readout of the desired pressure. The desired specific pressures will be applied and recorded for each trial. The desired pressure can be directly applied and will ensure the pressure is maintained at that level during the testing of the heart valve. The mechanical pump will come from a blood pressure mechanical pump where the tubing will adjusted to fit the plastic tubing that will be connected to the testing chamber. The plastic tubing that will be connecting to testing chamber will have easy remove/attach system for the mechanical and manual pumps as needed (Figure 2). Figure 4: Blood Pressure Mechanical Pump Artificial Heart Valve The two different heart valves that will be tested in this device are surgical and transcatheter aortic valves. Each valve will have its specific molding valve holder that corresponds to the desired heart valve. The bioprosthetic valve used in this design is the Edwards CEP Valve which has optimal hemodynamics and flow characteristics for treatment of aortic

7 7 heart valve disease. The artificial valve is a xenograft made from porcine leaflets. The transcatheter heart valve that will also be tested is Edwards Sapien XT which has optimal hemodynamic performance with Cobalt chromium frame with high radial strength for uniform leaflet joining (Figure 3). Figure 5: Edwards SAPIEN XT Transcatheter Heart Valve Dragon skin This component will be very important because it will keep the testing chamber, holding chambers, plastic tubing, necessary holes (for pressure pump, borescope lenses, etc.), heart valve mounting molding all secured by preventing any water leakage. Dragon Skin silicone is a high performance platinum cure liquid silicone compound with physical properties and flexibility ideal for this design. This material can sustain temperatures in the range -21 degrees Celsius to degrees Celsius with negligible shrinkage. With Dragon skin, strong and tear resistant molds can be made for heart valve mounting platform and secured the valve from moving while testing trials. Also its ability to stretch many times its original size without tearing and distortion. All the necessary holes at the attachment area will be filled along their diameter with Dragon skin to ensure very little solution leakage and maintain the system s pressure constant High Speed Camera The cameras that will be used during the experiment are Basler high speed digital camera. The Basler cameras have a pixel size of 5X5 micrometers and a resolution of 2048X1088 pixels or 2.23 megapixels. The maximum frame rate for the cameras is 340 frames per second. For our testing purposes though the frame rate used will not be that high due to the amount of memory that would be required to save and analyze all the images. The cameras will be mounted on two tripod stands for stability.

8 8 Figure 6: Images of the high speed camera and tripod that will be used in testing Borescope Lenses The borescope lenses will allow the high speed basler digital cameras to focus on a small area of the leaflets. Unlike zooming in with a typical camera lens which usually decreases resolution of the picture, the borescope lens maintains the picture quality. The borescope is also waterproof and can image from inside the testing chamber which allows the user to get an up close image of the leaflets. The boroscope lenses will be attached to both high speed cameras. Figure 7: Rigid borescope lens Platform The platform of the testing chamber will house the heart valve. The platform for the valve will be able to swivel, which will allow the valve to be repositioned without emptying the whole system. A series of small threads will be between the platform and the bottom of the chamber. This will make the valve move radially however not a significant change in the vertical direction. If the height of the valve was moved a significant amount the cameras would have to be recalibrated. The platform will have a hole in it to allow the leakage from the valve to flow into the spill tank. The platform will be specially designed to fit the silicone mold that surrounds the stent of the valve.

9 Calibration Before testing on each valve the cameras must be set up and then calibrated. This involves taking an image of a cube with known dimensions. This image will be used as a standard for size and measurements. Typically the calibration cube would be setup and imaged before the valve was mounted in the system. The calibration cube would be removed and replaced with the valve. It is crucial that during the transition from cube to the valve that the cameras are not touched. The new system will have a new calibration set up that will remove the timely transition between the calibration cube and the valve. The new set up will be able to accommodate both the valve and the calibration cube. The valve will be normally mounted in the system however the calibration cube can be placed in view of the cameras when desired and retracted during testing. The cube will be connected to a long narrow metal rod which will be partially inside and outside the tank. Figure 8: Calibration set up Venous Catheter One of the most important aspects of the system is that the chambers will be able to hold a significant amount of pressure and not leak. The system has many components such as the calibration cube and the borescope lenses that need to move horizontally.to allow these parts to go through the system and still maintain pressure a venous catheter will be used. Specifically a central venous catheter will be used because it is for larger veins and thus be able to accommodate the borescope lenses. The catheter works to allow the lenses and the rod for the calibration cube to enter the pressurized system however not let out any of the water.

10 10 Figure 9: Image of the venous catheter that will be used in the system Data Programs There are several programs that will be used during testing and after for analysis of the collected data. During experimentation the cameras will transmit the captured images to a computer program called XCAP for Windows. This program allows the user to change the number of frames to capture as well as many other features like brightness and contrast. The data collected during testing from the pressure sensor is recorded using the DataTrax software. The images taken by the XCAP are saved in a file and then imported into a labview program. The labview program is able to calculate the stress and strain of the leaflets. Markers are placed on the leaflets that are used for the analysis of mechanical properties at different pressures. The markers can be small pieces of graphite glued to the leaflet of water-soluble permanent markers as shown in the figure below. Figure 10: Image of leaflets with markers to determine stain Collecting Tank Some designs of transcatheter aortic valves, have a blocked view of the body of the leaflet and thus cannot be images from the top nor side. To still be able to analyze the leaflets the cameras image the leaflets from below the valve. Valves typically have a five percent leakage so water is

11 11 constantly flowing through even when closed. In order the capture a good image there must be a tank of water above and below the valve. The water above the valve ( the water inside the testing chamber) will be pressurized. The water below that valve will not be pressurized. The testing chamber will sit slightly raised inside of the collecting tank. When the tank is filled from the leakage through the valve instead of running out through a hole in the bottom of the tank it will spill over the top. The spill over will be funneled into a graduated cylinder where the leakage can be calculated. The reason for having the water spill over the tank is to keep a constant water level around the valve for imagining. Figure 11: CAD design of the holding tank. 2. Realistic Constraints 2.1 Engineering Standards The client has asked to have the project be designed so that machine can be able to test both bioprosthetic and transcatheter heart valves. It is essential that the containers that the valves are mounted in are capable of maintaining a constant high pressure setting. Maintaining the desired constant pressure is the most difficult part of the design. The reason this project has failed in the past is because the ultimate pressure range, which will be between 40 mmhg to 200 mmhg, could not be reached and kept constant. Another crucial standard for the design is being able to break each of the three leaflets into five sections. The reason for this is so that each valve leaflet can need to be analyzed closely. The final standard that is reached in this design is that there are two separate containers being used. The first container will be used to just hold the water and be connected to the second container which will house each valve. This setup style is chosen in order for the user to get a better view on how the three leaflets close when the pressure is applied on the valve.

12 Economic Constraints The client has provided this team with the majority of things needed for the design. The main constraint is on finding the best container to house the valves in. We want to make sure this container is strong and sturdy so that the needed inputted pressure will not damage the container or valves. The most expensive thing that needs to be purchased is another camera with a boroscopic lens. Only one camera with this specific lens is available to us and another one needs to be bought. Since the client is in fact providing us with the majority of the things needed for the project, the minimum of 1,000 dollar budget should not be an issue for our group. That being said we will make sure that we keep in mind of the budget and do our best to pay as little as possible for our purchases. 2.3 Environmental Constraints The project will have water running through the valves. This water will be supplied by Dr. Sun s lab and the group will do our best to reuse the water during experiments as much as possible. Also, saline solution is needed in the experiments so our team will do everything possible to make sure nothing toxic is going down the sinks. Lastly, the heart valves that are being used in the project can be dangerous to the environment and if for some reason the valve needs to be thrown out the team will make sure that it is properly disposed. 2.4 Sustainability This is where all of our concern is in our design. One of the main issues is going to be able to get the desired pressure in our containers and have it sustain it for the duration of the testing. This machine will be used numerous times and everything relies on the fact that reaching the appropriate pressure is crucial for the testing. Also, since the device is going to test each of the three leaflets individually, there needs to be a way for the pressure in the tank to stay constant as the valve is turned so the two cameras can capture good data on all three leaflets individually. This project will be created so that the user can easily clean and the tank after each use. There will be an easy way to just drain the water from the system since two separate containers are being used rather than just one. This makes it also very convenient for the users when they want to switch the valve being tested. Since the two separate containers are being used there s a lot less risk on something in the system getting damaged when the valves are being switched and the tanks are getting drained. 2.5 Manufacturability Since most of the objects used in the design are already provided not too many things need to be manufactured. The main thing that has to be created is the holding container for the

13 13 valves. This will require Plexiglas so the user can see through it and be able to easily view the valves. This container will be created in the machine shop so it can be designed the exact way that our team wants. The other thing that needs to be manufactured is the rotating valve holder. The client would like the valve to be able to rotate so that all three leaflets can be evaluated. Since this is a new design, this will also be created in the machine shop. This holder is going to be able to rotate and still be able to maintain the optimal pressure in the tank. It is important to make sure that the valve holder can stay still as the pressure is going into the container and then also be able to rotate when the next valve is being tested. The last thing that will be manufactured in this project is the tubing between the two containers. This connection tube needs to be able to hold the pressure and the water wanted without leaking any of it out. Without a good connecting tube this system would fail. 2.6 Social Constraints There are not many social constraints in this project, but the main one is time. This after everything has been manufactured and all the parts are available it will take a lot of time constructing this setup. A lot of modification may be needed in this project if the desired amount of pressure cannot be contained. If it seems that the pressure is leaking out of the container and the system is not reaching the necessary levels than something in the design process will have to be changed which will be very time consuming. This will require each of the team members to sacrifice and dedicate a lot of time to this project in order to have the project be successful. 3. Safety Issues This project is a relatively very safe design. There are not too many safety issues because this testing will be done in a very controlled environment. One of the safety issues that can be of concern is since there are two containers there has to be a tube that can somehow connect them. This tube could cause water leaking out of the system. When this water leaks it may leak onto the floor which could result in slipping. This will force the tester to be aware of the water leakage and see what it is doing in the remote environment. If the tube is correctly designed and attached in the project there should be minimal leaking that occurs. If the leaking does happen to be of a great extent it could cause safety issues in the lab. The testing will require the usage of both bioprosthetic valves and transcatheter valves. Since these valves are made out of biological tissue this could be hazardous to the users. The project tester needs to be aware that these valves can cause a biological hazard and the right precautions need to be taken. If the tester is dealing and handling the biological heart valves than gloves should be warn. Also, the user should make

14 14 sure the valves and the water does not get digested and they keep their hands away from the face and mouths as much as possible. When they are done the test it is also important to make sure that they wash their hands so all of the chemicals and any bacteria will get removed. Since these valves are bio hazardous materials it is crucial the proper handling by using, gloves and tweezers are used. There are not too many electrical devices that are used in this experience, but the two cameras, a computer, and the pressure sensor do need to be used. All of these three things are electrical devices and they will in fact be around the water in the system. It needs to be made sure of that none of these electrical devices are in contact with the water in the system. If the water gets into these devices it could be hazardous to the user. Water and electricity does not mix to well and this needs to e avoided. There are electrical outlets that are present all around the lab and it is mandatory the tester is aware of the leaking water and these electrical outputs to avoid any possible dangers. Also, this water will end up damaging these electrical devices and all of these devices cost a good amount of money. The last safety issues are around the manufacturing of the containers. These containers need to be created from scratch and also the screws and bolts need to be made. This will require our team to use the machine shop. All of our team members are machine shop certified so it will be important for us to make sure that we follow everything that is learned and all the right precautions are taken. Some of the materials like the steel bolts and screws, and the Plexiglas become extremely sharp when modeling them in the machine shop. This should not be of big concern though as long as our team members work in a safe manner. 4. Impact of Engineering Solutions This device itself will not have a direct effect on society because this project is created to give a lab the ability to test the strain of the valves under varying applied pressure for both transcatheter and bioprosthetic heart valves. This team is not responsible for making these valves which could one day get inserted into patients, but to rather design a testing device. This testing device can ultimately have a global effect just indirectly. If this design is created correctly and as planned this pressure system will be able to prove specific things about individual valves which could help to prevent problems from occurring with the valves before it is too late. Also, this device will have an impact on Dr. Sun s lab and other direct connections to his lab because this test will make sure that the valves being tested are suitable enough to continue on to other testing. This is important to figure this out before those long extended tests have been started and the excessively long time is wasted. The information that will be gained from this testing device could help to create different and more effective bioprosthetic heart valves. This could also globally have a significant impact. Heart valve replacement surgeries are common and generally very expensive. The design that our team is creating will be able to test these valves in an in vitro to help guarantee the patients replacement to be successful. Ultimately,

15 15 this will lower a large amount of fear from the patients knowing that numerous testing has been done. This could make heart valve replacements have a longer and higher percentage of success rate. This will give the surgeons the confidence also in the heart valves knowing that they have been rigorously tested to make sure they perform effectively. The device being created could also have an economic effect on society. This device will be able to obtain and analyze the effect of heart valves under a specific pressure. The most information possible about the valves can only help out the engineers trying to create these bioprostehtic valves. When all the mechanical properties of the biomaterials being used to create these valves are known they could possibly be able to alter and change the materials in the design to make it more cost efficient. If this becomes more cost efficient it will only have a positive impact on the hospitals providing the surgery and the patients paying for these specific valves. Also, the device will limit the amount of time spent testing valves that ultimately end up failing. This extra time will be more cost efficient for the labs which are paying for the valves and their employees testing the heart valves. 5. Life Long Learning There is a large amount of experience that everyone involved in this design project that everyone is gaining. For the most part everyone involved in senior design has never worked so extensively on one project. The experience that is being gained is something that each and every one of us will be able to take and apply to future jobs and consistently throughout one's career path. This team will also gain from working in an established biomedical engineering Lab that other teams and students will not get to experience. Being able to consistently being in a laboratory setting is something that as engineers is crucial. The knowledge and understanding from using the needed machines for our design will help us when we go out and interview for other jobs. One of the main lifelong lessons being taught throughout this whole senior design process is the skill learned with working in a group. In almost every profession and especially as an engineer it is crucial to be able to work well in groups. This is even more important to biomedical engineers who tend to work on very long and complicated projects that one person cannot just complete by themselves. Another thing being learned throughout this process is time management. This design project is very time consuming and even more difficult because we have to be able to coordinate around other classes and all of our teammates schedules. This is teaching each of us that sometimes we have to sacrifice some things that we do on our free time in order to coordinate with our teammates and to have a successful project. Another lesson that is being learned by group member of this project is the process of a project design. Before this project started none of us knew the amount of time and effort that is needed to be put into the creation of the device. There are so many factors that have to be

16 16 accounted for that was unaware originally of our teammates. Also, because there are project deadlines that need to be followed it forces the team to make sure we are keeping up with the design process and acknowledging all the different topics that we have to undergo. Some of these include the Project Statement, Proposal, specifications, and Optimal Design. Even though we are doing all these different processes for our class we also realize this is something that companies are all doing also every time they are creating a different device. This experience will help prepare us more for our jobs. Since Labview is something that is needed in our project design, all of our team members will become more comfortable with a scientific computer program. Computer programs like Labview are critical for almost any engineering company. This is because the precession and function of these high end programs are far more convenient and successful then things done just based off the users knowledge. Most engineering companies require a basic understanding in programming in order to get hired and this design will give us the experience that will be useful for our future careers. The last thing that everyone involved in our design will gain experience with the machine shop. Before senior design started none of our team members have ever created anything in the machine shop. All of us not are cleared and certified enough to work and create the different parts needed in our design. Gaining this understanding about the machines is important because now we can better comprehend the difficulty and what is entailed for any of the pieces to be created from scratch. This also will teach the preparation needed for the people in the machine shop in order to have them completely understand the dimensions and design of each individual part.

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