Platform design and experimental setup. Panel (A): The platform comprised (i) a supporting glass slide with a PDMS slab carved to accommodate the cell culture coverslip (f), (ii) a membrane-based vacuum system for the reversible sealing of (i), and (iii) the microfluidic channels, 0.2 × 0.1 mm (w × h), delivering fluids to the cultured cells (inlets in (a) and outlets in (b)). The assembled platform formed a 16 × 16 × 0.5 mm culture chamber (c) where cells were exposed to the fluid streams. The top layer embedded connections to the vacuum system (d) and to a pressure-monitoring auxiliary service (e). Panel (B) reports an image of the assembled platform, which was entirely optically transparent, operated flowing a color tracer (fluorescein) in 2 of the 8 channels. Panel (C): The micro-perfusion apparatus was essentially composed by the multilayered microfluidic platform, two syringe pumps, and a vacuum control system. The interface with a fluorescence microscope equipped with an environmental chamber is shown.
Model validation. Panel (a) reports representative results of the mathematical modeling showing concentration maps within the culture chamber. For a defined molecular species with its diffusion coefficient and fixed systems geometrical specifications, increases in the fluid flow rate change the shape of the compartment. Transport phenomena span from diffusion- to convection-dominated regimes following increases in flow rate. Panel (b) shows merged fluorescent images reconstructing the entire culture chamber, acquired during the experimental runs performed using parameters equal to the modeled ones.
Computational modeling of the infection process. is the theoretical relative efficiency of microfluidic perfused versus static infection. Panel (a) reports curves parametric in Pe and as a function of the square root of time. The horizontal line at (equality of perfused and static molar fluxes) separates the variables space where perfused-microfluidic () or standard static () infection conditions are favored. Panel (b) plots as a function of Pe at a defined time (t = 90 min) of infection. Finally, panel (c) plots the times at which for .
Static infections on HFF cultures. HFF were plated at a 100 cells/mm2 density, and all infections started 24 h after seeding. MOIs were: 50 in panel (a), 100 in panel (b), and 100, 200, 400, respectively, for the data points in panel (c). In panel (a), the plotted data points demonstrate how longer incubation times of cell cultures with the viral suspension led to increases in the infection efficiency. In panel (b), increases in the viral suspension volume (at a given MOI) led to reduced infection efficiencies; in parallel, panel (c) demonstrates that no significant changes in infection efficiencies were measured for increases in the viral suspension volume at constant viral particles concentration.
Comparison between static and microfluidic infections at different Péclet numbers for two cell types. Cell density was kept constant at 100 cells/mm2; MOI was 100, and infection time 90 min. Experiments were performed at and . Panels (a) and (c) refer to HFF cultures, (b) and (d) to MEF. Data were obtained via image analysis of cell cultures 48 h post infection. Panels (c) and (d) graph the modeled profiles for (the theoretical relative efficiency of microfluidic perfused versus static infection) and allow comparison with representative experimental results. Empty markers are for Pe = 10 and filled markers for Pe = 100. **. *.
Comparison between static and microfluidic infections for different infection times and at effective MOI. The results presented in panel (a) were obtained by exposing the cells to the viral suspension at MOI 10 for times ranging from 90 min to 12 h, both in static and microfluidic perfused culture. The use of microfluidics allowed obtaining higher efficiencies for longer incubation times. In panel (b), infections were performed at an effective MOI of 100 for 12 h and led to significantly higher efficiencies in microfluidic infections compared with those reached in static conditions. **.
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