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Alan - Turbulent Flows Ahead



So, change of plans on receiving the human islet cells for live testing. I talked to Charlie and he said that the human islet cell supplier might not be able to have any cells in stock for the foreseeable future. The problem with obtaining human islets is that they’re extremely hard to come by, since they have to be sourced from recently deceased, young, healthy organ donors. It’s understandable that there aren’t many “in stock”. I asked Charlie about subbing in mouse islets since those could be harvested at will, but he explained that each mouse only has a small fraction of the islets that a human does, so we would need to sacrifice 80-100 mice for just this project – an ethical choice that I am happy to avoid having to make. Fingers crossed that I receive them before I leave California though!

After the past two weeks, I successfully fabricated a few more hollow fiber cartridges that were suitable for in vitro tests. I tested them all for water flow rates with this pump setup, and collected pressure drop data for each of them. 

Charlie showed me this cool book on Molecular Transport Phenomena for biomedical engineering purposes, where I found this equation from Poiseuille’s law for modeling the fluid flow through my hollow fibers. 

It turns out that my collected pressure/flow rate data matched the expected values from the calculations, but they were all off by a certain factor (probably just a unit conversion error). Either way, it was super cool to see my fluid flow data correlate with a mathematical model.

Since I won’t be able to test any cells soon, I’m making the most of the little time I have left here by working with Nathan, who’s a mechanical engineer in the Roy lab. There’s a ton of cool design that has gone into developing both the artificial pancreas device as well as the artificial kidney device.

Charlie told me that they’re still seeing a significant amount of clotting inside the outer structures of the pancreas device when they implant it in pig studies, which they think might be from the sharp turns of the ultrafiltrate flow path. After talking with Nathan about the manufacturing and machining challenges of making the outer structures, he gave me some part files for the device which I’ve been able to open with Solidworks and explore using CAD. 

I figured out how to run computational fluid dynamics simulations (CFD) on the flow paths as well – here’s a picture of what the fluid velocities look like (most of the actual device is cut out for confidentiality). The red areas indicate fast-moving ultrafiltrate flow, which prevents proteins from having time to settle and clot. Blue areas indicate stagnant flow, which suggests clotting will occur. Hopefully I’ll have time to engineer some different possible flow path designs which might minimize this stagnation.



Other than that, I’m excited to be working more with the design side of the device and finishing up my time at the Roy Lab!  



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  1. TECJuly 28, 2018 at 7:57 AM

    Very cool. And it's a lovely example of a 4th degree function in real life - Q goes as the 4th power of R. These don't come up too often!

    ReplyDelete

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