The aneurysm portion of the project focused on creating a physically realistic benchtop aneurysm to study how a TPU printed stent could affect flow rate through the aneurysm. The aneurysm model was found online through a research paper published on ResearchGate that has more than 100+ 3D scans of real patient aneurysms.
There were two specific things I was thinking about while choosing the model 1. Easy access to insert the stent 2. No Cupping The model was scaled up 7x and then printed on the 3BL. It was scaled up so that I could successfully get a functional stent that could 3D printed using TPU. I had to ensure that I could actually insert the stent but ALSO get the stent out. The stent was modeled to snug up around the surface of the aneurysm so that the stent would wrap around the curvature of the aneurysm model. Due to printing this using the Formlabs, I had to ensure cupping wasn't a possibility. I've heard horror stories of cupping and I did not want to become one of those people, and I also wanted my part to come out as precise as possible. I applied custom touchpoint sizes as well as lattice structures for easy removal and a smooth surface finish so that my stent could not get sliced by a small sharp touchpoint.
The assembled system was integrated into a closed-loop flow setup driven by my peristaltic pump, enabling repeatable testing and visualization of flow behavior through the parent vessel and aneurysm sac.
Pump
This was the portion that took the longest just due to the fact that I had never done modeling projects like this before.
I CAD race. That's what I do. And this was NOT CAD racing
This design was inspired by a Youtuber called PattysLab. Every part of this design dynamically changes itself through the equation.txt file. If you change 1 value, all of the other dimensions will change as well. Due to my extensive work in my universities print lab, I understand the importance of tolerancing as well as how to do it. Everything is toleranced perfectly and you get tight, nominal, and loose fits exactly where you need them. The best part... 0 supports. This design is user friendly and allows for any person with 0 printing experience to still get a perfect print every time.
The hardest part of this portion of the project was just getting enough torque to actually get the pumping action. Originally, my entire design was going to be a lot smaller since I wanted to get as close as possible to an actually aneurysm mock loop. It did NOT work. I explain more at the bottom of this page as to why.
Stent
This stent is made out of TPU with a hardness rating of 95A. The biggest challenge I had to face while printing this is how I would could get a large enough stent that won't fail during a print. Most 3D-printed materials can use removable supports made from the same material, but TPU doesn’t work that way. If you try to print TPU with TPU supports, you will just fuse the part together.
I have a Bambu P1S at home which is what I used for this entire project and you could say that with my AMS I could do TPU for the part and then PLA for the support but you can't. The reason is because you have to ensure that each material is flushed out completely from the nozzle or else you will still get fusion between supports and part. This is costly as well as extremely inefficient. So, I opted for another strategy.
I used my schools 3D printer
I printed the stent on a Prusa XL. 1 tool head was the TPU, 1 tool head was PLA. This allowed for easy removal and the part came out perfect.
How a part of this project failed
Originally, I was going to use 3mm ID & 7mm OD tubing. I thought I would be able to squeeze this tubing but I just did not have enough torque in order to achieve full occlusion. My motor was still not strong enough so I opted to switch to 5/16" ID tubing.
My pump could achieve a flow rate of 6.53 L/min using 5/16" tubing but I could not get any flow measurements due to materials I had on hand. I originally attempted to measure using my schools Sensirion SLI-0430. This sensor was great for my Glaucoma lab in my Biofluids class but not good at all for my use. Why? Because it's meant to measure >55µL/min and I was definitely going way past that. I also couldn't get flow through the sensor due to air pressure being greater than the pressure of water exerted through that section of tubing so flow would not even go through. That is why my setup (video to the left) has the flow exit higher than the flow measurement section since I was trying to have gravity work with me.
So, the peristaltic pump worked great. Every 3D printed part worked great, I just had too much oversight in what was possible with my equipment. It is possible. But not with my setup.