Barrett Chamber Flow Visualization
Barrett Chamber Flow Visualization
For my lab rotation here, I was tasked with visualizing the flow of blood/blood-like objects across the 1st generation Barrett chambers.
The design of the chamber is seen below. Some key characteristics are that the chamber is suspended from resting flat on a surface to allow liquids to diffuse through the membrane, and that there are 5 permeable channels which are not isolated from one another; the fluid can move from channel to channel.
DIC light microscopy was used to provide contrast between the different materials under 40x magnification. Glass nanobeads (average radius = 5600nm) and blood were diluted separately with DI water and flowed through the chamber at various speeds (10 microliters/minute standard) using a syringe pump. By varying focus manually, a tomogram of many different heights within the Barrett chamber was assembled. Videos were taken at 15 frames/minute with autocontrast settings applied and assembled into a video by the custom MATLAB code available in the microscope rooms. Ideally, I would expect to observe particles flowing across the filter above the pnc-membrane, exiting through the outport, without the particles penetrating through the filter to the other side.
Red Blood Cell Flow Over pnc-Si Filter Video (1 microliter/minute)
Blood Cells Flow Through Ruptured Chamber Video (15 microliter/minute)
The first two videos show tomograms of blood flowing over the filter’s permeable regions, from above to below. The first video demonstrates the impermeability of the blood cells, as no cells diffuse through the channel and come out below in the tomogram. In the second video, a ruptured chamber makes cells leak around the outside of the permeable regions and sizeable blood flow is observed below the chamber. The surface of the membrane appears wrinkled; deformations occur when the membrane does not have equal stress on each side (ie the membrane was not immersed).
Nanoparticle Tomogram Nonimmersed: Video 1 and Video 2
Similar to the red blood cell tomograms, each of the nanoparticle nonimmersed tomograms show impermeability to the nanoparticles, and a wrinkly surface of the membrane. The nanoparticles and the blood cells both adhere to the surface of the membrane if not flowing over them, and particles only become loose when a Newtonian collision occurs and the inciting particle becomes trapped.
Nanoparticle Tomogram Immersed, Ruptured Chamber, Central Channel
Nanoparticle Tomogram Immersed, Ruptured Chamber, Peripheral Channel
For the two immersed tomograms seen above, the membrane surface is smooth, due to the stress on both sides of the membrane being equalized. In the tomogram of the central channel, the flow above the membrane is good, however beads are present below the membrane due to a chamber rupture near one of the peripheral sides. The flow below is in an opposite direction to that of the flow above. The tomogram of the peripheral channel opposite that of the ruptured side doesn’t show any beads below. There are a large number of beads that are adhered to the membrane in these videos; water with the nanoparticles mixed in was allowed to sit in the chamber overnight from previous experimentation.
From Dean’s discussion at the last NRG meeting, I made another observation under the microscope that wasn’t captured on video. The initial flooding of the chamber appeared pyramidal (Dean’s video here), with the central permeable channel flowing the quicker than the peripheral channels. However, I’m not sure if his channels were isolated from one another in the model; here all the fluid is contained in one chamber.