Injection Catheter for Stem Cells Adam Goon, Michael Conrardy, Joel Webb, Andrew Bertram

1. Injection Catheter for Stem Cells Adam Goon, Michael Conrardy, Joel Webb, Andrew Bertram Client: Dr. Tim Hacker, PhD (UW Department of Medicine) Advisor: Prof. John Webster (UW Biomedical Engineering Department) Motivation Budget Final Design Abstract Three component guided catheter The purpose of this project is to create a catheter that can provide multiple injections in a reduced amount of time compared to the current procedure. The catheter will be used by the client in his research of injecting stem cells into the heart to determine if it will produce new cardiomyocytes of the heart. The final design consists of three components that can provide multiple injections at different locations in the ventricle. The design has adjustable height and can be rotated 360 degrees, so all walls of the ventricle can be reached. The final prototype would be made of extruded polyurethane with an injection catheter that has a nitinol needle for injections. Estimated cost to extrude polyurethane for true-to-scale catheter in UW Polymers Lab: $5000 • External Component • Flexible tube in which internal component is inserted • Contains small slots from which needle can exit • Contains a rectangular track to assure internal component is linearly aligned with slots • 9 French (3 mm OD x 2.25 mm ID) Testing Background • Accuracy Testing • Positioned catheter a fixed distance from graph paper (3.5 in. or 88.9 mm) • 12 trials of marking where needle contacted paper • Inner component height kept constant during all 12 trials • Determined mean point of all 12 trials • Standard deviation showed how far each injection would be from mean point • Y-distance determined to compare to distance between holes on outer component • Current research is being conducted involving the injection of stem cells into dead heart tissue • Research will determine to what extent stem cells can regenerate dead or damaged heart cells • Our client is using a single injection catheter (Myostar by Biosense-Webster, see Figure 2) that must be repositioned for each injection site on pigs • The procedure involves the use of x-ray imaging, contrast agent and an ECG to determine the placement of the catheter on the heart walls (see Figure 1) • Currently, no catheters to provide multiple injections in the heart Figure 3: External component with 14 slots and a track for internal component to travel along • Internal Component • Solid tube inserted within external component • Contains rectangular extrusion in which track of external component would travel • Contains circular track for injection component • Guides injection component out of holes along external component at ~60 degree angle Figure 8: Scatter plot of 12 points of injections at 3 different hole locations Figure 1. An X-ray image of the catheter inside the left ventricle during a procedure • Standard Deviation • x-direction: 3.05 mm (0.36 mm)* • y-direction: 3.56 in. (0.42 mm)* • Y-Distance between mean points: • Hole 6 to 7: 20.32 mm (2.40 mm)* • Hole 7 to 8: 19.30 mm (2.28 mm)* • * Estimated measurements in true-to-scale design Figure 4: Internal component with circular track for injection component. Extruded track to go along external component • Injection Component • Follows circular track of internal component • Polyurethane tubing with lumen for stem cells • 3 mm long, 27 gauge nitinol needle at tip • Protrudes up to 25 mm from internal component into left ventricle • Current use of single injection catheter is very time consuming • The heart is still beating so moving the catheter around is difficult • Needle depth is inconsistent due to different bending angles • Alternative catheters are not flexible enough to pass aorta and enter ventricle Future Work • Determine method of rapid prototyping or plastic extrusion to create prototype of true-to-scale catheter • Determine optimal slot size without affecting structural integrity of catheter • Develop mechanical handle to ensure proper alignment of holes and track • Test for accuracy, consistency, and time reduction of procedure on true-to-scale prototype • Test lengths of needles to determine which size will work best in true-to-scale design Figure 5: Injection component with polyurethane tubing and a 3 mm long nitinol needle on the end for injections Figure 2. Current catheter used to inject stem cells. The catheter incorporates a single retractable needle at the tip [1] • Materials: • Polyurethane will be used for interior and exterior • 27 gauge nitinol needle used on the injection component • Current catheter can be used for injection component Client Requirements Dimensions • Multiple injections: The catheter must be able to create multiple, quick injections to decrease time of procedure • Size: Must be small enough in diameter to fit through the arteries and aorta of the body • < 14 French diameter (4.66 mm) • Flexibility: The catheter must be made out of flexible enough material to curve through the aorta • Consistency: The needle must enter the muscle wall of the heart with a constant depth • Accuracy: The catheter must be positioned in the heart to improve accuracy of injections at the same location Internal Component External Component Acknowledgements Special Thanks to: John Webster, Professor, UW-Madison Biomedical Engineering Dept. Tim Hacker, UW Department of Medicine Amish Raval, Assistant Professor, UW-Hospital Tim Osswald, Professor, UW-Madison Mechanical Engineering Dept. and Polymers Lab [1] http://www.med.upenn.edu/mcrc/patel_lab/documents/LVCatheterUsingEtOHinSwineJICE.pdf [2] http://www.memory-metalle.de/html/01_start/index_outer_frame.htm [3] http://www.alzet.com/products/Alzt_cathrs.php References Figure 6: True-to-scale internal component with dimensions Figure 7: True-to-scale external component with dimensions