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. 2019 Aug 20;10(8):551.
doi: 10.3390/mi10080551.

A Passive Microfluidic Device for Chemotaxis Studies

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Free PMC article

A Passive Microfluidic Device for Chemotaxis Studies

Maria Laura Coluccio et al. Micromachines (Basel). .
Free PMC article

Abstract

This work presents a disposable passive microfluidic system, allowing chemotaxis studies, through the generation of a concentration gradient. The device can handle liquid flows without an external supply of pressure or electric gradients, but simply using gravity force. It is able to ensure flow rates of 10 µL/h decreasing linearly with 2.5% in 24 h. The device is made of poly(methylmethacrylate) (PMMA), a biocompatible material, and it is fabricated by micro-milling and solvent assisted bonding. It is assembled into a mini incubator, designed properly for cell biology studies in passive microfluidic devices, which provides control of temperature and humidity levels, a contamination-free environment for cells with air and 5% of CO2. Furthermore, the mini incubator can be mounted on standard inverted optical microscopes. By using our microfluidic device integrated into the mini incubator, we are able to evaluate and follow in real-time the migration of any cell line to a chemotactic agent. The device is validated by showing cell migration at a rate of 0.36 µm/min, comparable with the rates present in scientific literature.

Keywords: chemotaxis; diffusion; mini incubator; passive microfluidic device.

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
(A) Device scheme (not in scale); (B) CAD drawing of the microfluidic device; (C) exploded view of the device. All the CAD files can be found in Supplementary Materials.
Figure 2
Figure 2
Experimental set-up used to characterize and validate the microfluidic device: mini-incubator and microfluidic device (MFD).
Figure 3
Figure 3
Isometric view of the microfluidic device (A); the device in the loading phase of the dyes appears as in the figure (B), while at the end of the experiment there is a fairly uniform concentration within the central reservoirs and in the drain ones, maintaining, however, two flows at different separate concentrations (C). We also report the time-lapse acquisitions of the channel at the most significant time instants (D).
Figure 4
Figure 4
(A,B) Simulation of the food dye concentration gradient: the concentration gradient of the dye within the transversal channel is linear only after 192 h, due to the low value of the diffusion constant; (C,D) simulation of the interleukin-8 (IL-8) concentration gradient: unlike the food dye, the concentration gradient of the interleukins becomes linear after almost 60 min; (E) the concentration values were calculated according to the pixel intensity of images taken in time-lapse along the transversal channel and are therefore expressed in arbitrary units, we report the pixel intensity as a function of the distance 8 h after having filled the device with the blue dye; (F) gradients of concentration of the food dye as a function of the channel position at different times; (G) simulated trend of the concentration gradient within the transverse channel, values expressed in mol/m3; (H) real trend of the concentration gradient.
Figure 5
Figure 5
Graphs of the gradients as a function of time obtained during the experiments with dyes in which: (A) 3000 µL of water + dye and 3500 µL of only water were loaded respectively in the two source reservoirs; (B) 3500 µL of water + dye and 3500 µL of only water were loaded respectively in the two source reservoirs; (C) 3750 µL of water + dye and 3500 µL of only water were loaded respectively in the two source reservoirs; (D) 3961 µL of water + dye and 3500 µL of only water were loaded respectively in the two source reservoirs.
Figure 6
Figure 6
Cells media within the device (A); chemotaxis of a single cell (B). Cell movements could be observed after about 175 min. The average speed of cell movement was about 0.36 μm/min.

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