Alan - Fibers, Fibers Everywhere

Hey everyone! It’s been a while since my last blog post – I’ll chalk that up to being so busy these past couple of weeks with lab work and other things. Going into my fourth week at the Roy lab, it’s hard to believe that my time here is flying by so quickly already, but here we are. 

After my first week at the lab, I started working on my independent project. As I mentioned before, my lab works with creating bioartificial organ devices, specifically an implantable artificial pancreas. Once implanted, the patients blood goes through the device and through diffusion, an ultrafiltrate is produced by passing the blood across a silicon nanopore membrane (SNM). (here’s a picture of one of those silicon nanopore membranes I keep talking about - the rainbow is from refracted light, not actual coloring) 

This ultrafiltrate is mostly just blood plasma, but it has a couple of key ingredients: dissolved oxygen, glucose, and other nutrients. The ultrafiltrate is then fed through an agarose gel, which has islet clusters (pancreas cells) suspended in it. The cells take in the dissolved oxygen and glucose, and produce insulin that’s fed back into the ultrafiltrate, and then back into the bloodstream.

Some of the problems that the device is facing is the density of islets in the gel. The current method for making the gel involves poking many small wires through a mold as the gel sets, leaving these thin channels for the ultrafiltrate to flow through. There aren’t enough of these channels though, and they’re too far apart for the islets to really extract anything from them. So, my project involves exploring alternate methods for creating these channels using hollow fibers. 

The hollow fibers that I’m working with are made out of polyethersulfone, a type of porous plastic. Normally, I would praise the wonders of this plastic’s filtration properties (they can filter out molecules as small as certain antibodies or insulin), but it turns out that the fibers are so light that their static interactions make them fly everywhere whenever I try to work with them. 

But once I was able to collect a bundle of reasonably straight fibers and tape them down, I then threaded them through a unit that I made from a couple of tubing adapters. Here’s a picture of the basic setup, as well as what they look like after slicing the ends flush to the connectors. I tried a variety of epoxy resins and silicone glue to “pot” the fibers, or basically hold them in place at the ends of the tube. I finally settled on a type of aquarium silicone glue, which I was able to slice through once it was done drying, to create a flush seal at the ends.

There are actually 36 individual fibers inside of each test unit I’m making – I actually derived this number from calculations on fiber density and diffusion radii, as well as optimizing for fluid permeability. Really cool to be able to apply design principles that I learned in engineering classes at school to biomedical problems in lab.

# of Fibers	Fiber Density
16	6.7%
24	10.0%
36	15.1%

I then connected the units to a pump, flowing water through at a very slow rate (20 microliters/min!) to see if water would penetrate the fibers and test for any leaks. The results were pretty promising, so I injected some microparticle solution to simulate the eventual in vivo tests I would be conducting.

Microparticle solution involves extremely small pink beads that are around the same shape and size of mouse islets. By putting this solution into my hollow fiber units, I can see how islets would interact with the geometry of my unit, without having to deal with the problems associated with living cell cultures.

As you can see in the picture, the microparticles are pretty clustered around the outside of the fiber bundle. This is a bit of a problem – I need the particles/islets to be evenly distributed within the unit to ensure that diffusion and ultimately, cell survival, is as high as possible. There’s also the problem of the fibers being twisted and compacted, which just happens as a part of the assembly process. Because of how small and fragile the fibers are, it’s difficult to control their positioning. Hoping to solve this next week with some alternative solutions I’ve been brainstorming with Jimmy, one of the engineers in the lab.

Here are some microscope images of the sealed ends of the units. As you can see on the top left, the silicone is really viscous and doesn’t seep in between the fibers as well as I’d like, creating a large air bubble that could be prone to leaks. The middle picture is more ideal, with all the fiber ends open and sealed. But sometimes the fibers come flattened like on the right image, leading to lower hydraulic permeability. All three still have the problem of randomly patterned fibers, which is something I’m hoping to focus on solving next week.

Also, I finally had a chance to meet with Shuvo, my PI. We talked briefly about the lab and my transition, as well as some of his goals for my time here. It was exciting to hear that he truly wanted me to have a great experience at his lab, and that my independent project would have measurable impacts on the development of the future iBAP device. Shuvo then explained that “Not all research has a clear answer. If it was about finding an answer, or making one, it would be development. Hence, R&D, or Research, and Development. Thus, there are no failures in research, simply more knowledge.” This distinction was really important for me to hear, as I’d been pretty consumed with trying to figure out a way for my project to merge seamlessly with the device in its current form, instead of focusing on figuring out the basic knowledge of what is and isn’t possible.

And a little on the lighter side – Rohit, Michelle and I had the chance to go to SF Pride this past weekend. The SF Pride Parade is one of the biggest pride events in the nation, and the enthusiasm from the crowd certainly echoed that. It’s a public festival that goes right through downtown Market St. and ends up at Civic Center Plaza. It was really cool to see a city come together around a singular cause, as well as being exposed (quite literally, @nudists) to a different kind of culture than the East coast.