(Digital Presentation) Design, Flow Simulation and Experimental Test of Micro/Milibioreactor with Pillar Structures for Bubble Control and Cell Growth
Authors: Bourguignon Natalia , Bravo Elisa , Chamorro Daniel , Aravelli Aparna , Perez Maximiliano , Lerner Betiana , Bhansali Shekhar 
Published: November 2022

The demand for Lab on a Chip (LOC) devices, such as microbioreactors, has driven microfluidic research and technology. With the capability of controlling the environment and monitoring results in real-time, microfluidic devices are highly advantageous in the application of cell culture. On the other hand, micro/nano-scale bubbles have become a field of growing interest for addressing many challenges in LOC applications. In this work, we present a novel microfluidic bioreactor based on a micropillars design that reduces stresses caused by bubbles on the cell growth in the microchip. The combination of one chamber with 3-pillars and 10-pillars design with the channel heights of 270 µm and 2 mm was evaluated.

To obtain the optimal architecture, computational fluid dynamics (CFD) simulations using SolidWorks Flow Simulation Software were created to characterize the designs. Simulations are essential to assure that the washing of cells and bubbles do not occur in the fluid and to weeding out the designs that are suitable for cell growth. Numerical results showed that the velocity is high at the inlet and outlet when compared to the interior portions of the chamber. A higher flow rate and velocity were observed during the filling time in the 10-pillars design (3.0 x10-4 m/sec) in comparison with the 3-pillars design (2.4 x 10-4 m/sec). Also, a more homogeneous filling pattern was observed in the 3-pillars designs. This behavior occurs because the increased number of pillars manifests with a greater number of nuclei of flow disturbance, and more centers of agitation, resulting in a more heterogeneous flow. Pressure is homogenous for both 3 and 10 Pillars designs with slight changes from the inlet, with higher pressure, to the outlet, with lower pressure.

The microfluidic devices were manufactured using flexographic master mold (Fmold) technology and polydimethylsiloxane (PDMS 10:1) as substrate. The total liquid capacity of the microchips was calculated as 205.5 μL for 270-um-height and 1522 μL for 2-mm-height. An experimental flow test with methylene blue using the syringe pump, with an inlet flow rate at 2.5 μL/sec, and image analysis from video using ImageJ software was performed. The experimental results were found to be comparable to the simulations results. When the number of pillars and height of the chambers increased, a higher flow rate and velocity were observed during the filling time. In this context, the 3-pillar design with 2 mm height was considered the most suitable design for cell culture applications. In addition, the 2 mm larger height design was tested for bubble control, and the results showed some of the bubbles were easily removed by applying flow rate, and the ones that remained inside the chamber did not block the channels in the pillar’s designs without affecting the system.

The present platform has a simple architecture, inexpensive manufacturing methods, ease of operation, and the ability to use different types of cells. The pillar milli-bioreactor system has the advantages of bubble control, a large volume of work, real-time monitoring, and a suitable microenvironment for cell culture with prospects for future health applications.