Figure 4.

Cell viability. (a) Schematic representation of the microfluidic workflow used for the characterization of H1975 and HL60 cells viability in droplets. Cells were encapsulated in droplets with medium and incubated for 72 hours. A fluorogenic assay (Calcein-AM) was then injected in each droplet allowing the fluorescent detection of the droplets containing living cells. (b) Image of the electro-microfluidic injection system. The white arrow indicates the droplet flow direction. The green arrow indicates the presence of a cell. When the droplet passes by the injection arm, it is locally destabilized by applying an electric field. The field ruptures the film separating the droplet and reagent, allowing the reagent to be injected. Scale bar: 100 µm. (c–e) Green fluorescence histograms depicting negative (black) and positive (red) cell count events. (c) Signal recorded at cell encapsulation with the fluorogenic assay added in bulk. 9,150 cells were counted out of 56,567 droplets resulting in λ = 0.16. Inset shows cell distribution with Poisson fit as a straight line: λ_fit = 0.17 ± 0.004 with R² = 0.99. (d) Signal recorded 72 hours after cell encapsulation. 13,865 cells were counted out of 105,781 droplets resulting in λ = 0.13. Inset: λ_fit = 0.14 ± 0.002 with R² = 0.99. (e) Signal recorded at encapsulation with the fluorogenic assay added drop-by-drop using the electro-microfluidic device. 8,127 cells were counted out of 51,054 droplets resulting in λ = 0.16. Inset: λ_fit = 0.17 ± 0.004 with R² = 0.99. (f) HL60 and H1975 conditional viability following 72 hours of incubation in droplets. HL60: λ_t=72h/λ_t=0h = 0.61 ± 0.07 (mean ± s.d, n = 2). H1975: λ_t=72h/λ_t=0h = 0.77 ± 0.04 (mean ± s.d, n = 3).