Biomedical Engineering Capstone
In my senior capstone, our team developed an innovative medical device to address liver perfusion challenges during transplantation, in collaboration with Paragonix. Below you'll find the key stages - from initial research through final presentation - with links to more documentation.
This project was a semester long effort in collaboration with Katie Lew, Anupama McCulloch, and Stephen Albright.
Project Overview
Livers only have a short window of time to be transplanated after removal from the donor. Paragonix is working on a device to perfuse the liver with perfusate to extend this time to up to 48 hours. Our team developed a cannula prototype to connect the liver portal vein to the Paragonix device in a safe ane secure fashion.
Existing Solution
Currently, Paragonix uses a barb cannula to connect the liver portal vein to their device. The cannula is inserted and a suture is tied around to secure it in place. This solution creates a good seal, however it causes significant damage to the portal vein, meaning surgeons on the receiving end have to remove a section of the portal vein and reattach it to the liver.
Engineering Requirements
Before we started ideating, we noted some of the engineering requirements our cannula had to meet. Of utmost importance was the seal quality of the cannula, and the strain on the portal vein, since we want to minimize damage to the transplant site.
Design Constraints
We brainstormed quite a few different design ideas, everything from magnets and suction methods, to adhesives and mechanical clamps.
Prototyping
We eventually settled on a 2 part design that uses a silicone ring and a tapered inner cannula. The silicone ring slides around the outside of the portal vein, and the tapered inner cannula is inserted into the portal vein. The two are brought together to create a seal, and the silicone allows for a better seal with less compressive force. Our first successful ideation indicated this was a plausible design, however the attachment mechanism between the ring and the body of the cannula needed some attention. We created this intial design using reversable zip ties, which demonstrated the concept. However when we got to test it in a porcine model, the zip ties got in the way of cannulation, so we moved onto more flexible designs.
Final Prototype
Our final prototype used the same silicone ring and tapered inner cannula design, but we replaced the zip ties with hinging arms that could swing down during cannulation, and swing back up to secure the cannula in place. This design was much more flexible, and it had ridges for the arms to lock into place, with the added benefit of both a tactile and auditory feedback.
Testing
We ran a series of tests to validate our design, including this pictured leak test. We attached our cannula models to a peristaltic pump and measured leakage across hour long periods at 5 minute increments. We also tested user experience by having fellow peers try to cannulate and timing and measuring their experience. We found that our design created a significantly better seal than the existing barb cannula by nearly 66% less leakage on average. Our cannula took an average of 2 minutes and 14 seconds to cannulate, which was slightly slower than that of the barb, however we believe the tradeoff for security and safety is worth this small time.
