(H-318) Optimization of the assembly for a disassemble milli-fluidic bioreactor

Introduction::

Mechanical forces have been shown to affect cell migration, behaviour, and interaction. To model cell behaviour under differential shear forces in vitro, many bioreactor systems have been developed, including cone and plate bioreactors, microfluidic and millifluidic channels, and parallel plate reactors. Though each has its advantages, micro and millifluidic channels have the advantage of ease of production, low cost, and choice of materials, which can also be used to affect cell behaviours. The channels are also highly tunable, in terms of cross sectional shape, size, and flow delivery, that make them applicable to many biological applications. However, a challenge with the micro and millifluidic channels that many people face is leaking during fluid flow through the channel, especially at high shear rates and in cases where permanent bonding is not used to adhere the two sides of the channel (i.e. when disassembly is needed). Leaking can lead to fluid loss and an alteration of flow streamlines and shear stress levels. Therefore, to reduce leakage from millifluidic channels, we have tested different materials, sealing techniques, and channel housing designs in order to maximize ease of assembly while eliminating leakage over different shear conditions. For this project, we have chosen to focus on a 3D printed disassemble milli-fluidic channel design, which allows us to apply shear stress over long periods to cells and study cellular behavior in vitro. 

Materials and Methods:: The SLA printer Form 3B was used to 3D print device components using Formlabs resins BioMed Clear and Flexible 80A. To assemble the flow bioreactor, the flow device was encased using glass coverslips and a hard outer casing. Vacuum grease was used to create a fluid-tight seal between the flow device and glass coverslips. Eight slotted screws were then installed into the hard outer casing to apply compressive force on the assembly, giving this assembly procedure the name “rigid compression with eight screws”. In an alternate assembly method called “flex compression with four screws,” (Fig. 1) a soft, rubber-like compressing layer made with Flexible 80A resin was placed between the glass coverslips and hard outer casing. After the introduction of the soft compressor, the number of screws was reduced to four screws in order to further decrease assembly time. The screw placements are B, D, E, and G as indicated in Figure 2.

Results, Conclusions, and Discussions::

Leak-proof flow was reliably established with the “rigid compression with eight screws” assembly method. However, assembling the device this way was time-consuming and cumbersome, as the glass coverslips would often crack even when carefully installing the screws into the casing after the entire sterilization process. In order to mitigate the risk of cracked glass, a soft, rubber-like compressor was placed between the glass coverslips and rigid casing, and this resulted in no cracked glass with the maximum compression level the screws provided. However, leak tests of the “flex compression with four screws” method did not reliably establish leak-proof flow through the bioreactor. So, while it did make the assembly process more efficient, leak-proof flow could not be guaranteed. Possible reasons for this include: (1) insufficient compression force, (2) insufficient vacuum grease, and (3) the geometry of the flexible compressors does not apply the compression force uniformly across the glass coverslips, making leaking viable where there may be less compression. 

While leak-proof flow was not reliably established with the “flex compression with four screws” method, the assembly process was significantly easier and much faster than the “rigid compression with eight screws” method. It is important to make this process more efficient because it means less time and resources are wasted to achieve an experimental result for the researchers using this flow bioreactor for their own research. In order to achieve both a more efficient and leak-proof assembly method, the “flex compression with four screws” process could be optimized with methods such as changing the geometry of the flexible compressors, increasing the screw count, and ensuring enough vacuum grease is applied.

Acknowledgements (Optional): : My work and knowledge gained would not have been possible without the help of Dr. Jane Grande-Allen and Dr. Jennifer Connell and all members of the Grande-Allen Lab at Rice University.

References (Optional): : Silverio V, Guha S, Keiser A, Natu R, Reyes DR, van Heeren H, Verplanck N, Herbertson LH. Overcoming technological barriers in microfluidics: Leakage testing. Front Bioeng Biotechnol. 2022 Sep 7;10:958582. doi: 10.3389/fbioe.2022.958582.