Introduction
As discussed in a previous post, we are working to adapt a PDMS flow insert as a manufacturable component. While our priority was maintaining the original flow channel geometry as Mansouri et al. designed, we slightly changed the channel length (5 mm –> 4.6 mm) to accommodate an extra bonding area for the pressure-sensitive adhesive (PSA). This change does not significantly impact the uniform shear stress profile at the membrane (validated by the COMSOL model shown in Figures 1 and 2). Additionally, this confirms the flow is fully developed before reaching the membrane.
Figure 1. A. Manufactured flow insert, with a molded PDMS top layer and PSA/PET/PSA channel. B. Shortened channel dimensions maintain uniform shear stress at the culture surface.
The shear stress values at the culture surface across the length of the membrane were calculated to be 10.661 dynes/cm2 for the revised channel and 10.657 dynes/cm2 for the original channel at a flow rate of 580 µl/min (Figure 2).
Figure 2. A. Defines channel length of shear stress values plotted in B. B. Shear stress values across bottom of flow channel at a flow rate of 580 µl/min.
V1 ALine Flow Insert
We recently received a test batch for this design from ALine. The inserts are delivered in an array and require separation using a sharp blade. The assembly process is detailed in Figure 3.
Figure 3. Assembly process for manufactured flow insert.
ALine performed a leakage test and found that the PSA provides a tight seal, preventing leakage from the channel (Figure 4). In-house testing confirmed alignment of the insert with the open well of component 1 as well as a tight seal between the PSA layer and the membrane surface.
Figure 4. Leakage test performed at ALine, demonstrating a tight seal between the PSA and glass slide.
Initial inspection of the inserts showed promising optical clarity when compared to the in-house PDMS (Figure 5).
Figure 5. Phase images taken at 10x in a microslit membrane device, showing comparable optical clarity between the in-house and ALine PDMS.
However, when imaging at lower magnification (4x), we noticed lines on the top surface of the channel that significantly interfere with imaging, as shown in Figure 6.
Figure 6. Lines on top surface of PDMS channel cause phase imaging issues at 4x.
To test biocompatibility, we seeded HUVECs in NPN devices with either the ALine or in-house insert.
Figure 7. Loss of HUVEC viability after 12 hours of culturing in ALine insert.
We hypothesize that this loss of cell viability is due to (1) poor gas exchange or (2) a toxic substance is leaching out from the insert. We are currently testing the toxicity hypothesis by culturing HUVECs in a 24-well plate and placing the insert in the well to observe potential cell loss due to the material itself.
The in-house inserts are sonicated in a beaker of ethanol to remove any potential harmful agents. We could also test sonicating the ALine insert, although this may affect the PSA layer. Additionally, we will request the inclusion of a blue backing layer on the insert (similar to other μSiM components) as an added measure of sterility. More improvements to come…
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