Extension of the feedback system to stabilise average cell encapsulation concentrations in microdroplets. (a) Micrograph of the cell encapsulation device, consisting of an aqueous inlet for cell suspension samples which is diluted and flow focused by a dilution buffer, followed by flow focussing with an immiscible oil to form microdroplets. (b) Graph showing the variation in droplet volume (red) and average red blood cell count per droplet (yellow) when using syringe pumps. Cells placed in a syringe without density matching quickly settle and the concentration of cells encapsulated quickly falls (yellow curve). By density matching the sample to the cells, there is a slow drift in encapsulation concentration. (c) Graph showing the change in volume (green) and cell count per droplet (yellow) for pressure based pumps without feedback (time < 0) and with feedback (time > 0). Drift in the cell count is also present when using pressure pumps, as can be seen before feedback is turned on at time = 0, however this can be compensated for by feedback to alter the dilution factor. (d) Extracted rate of change of the cell count per droplet when using pressure pumps with and without feedback for density matched and non density matched red blood cells. The plots show the mean gradient of linear fits to the cell count per droplet over a thirty minute period, error bars are the standard deviation (N = 3). Scale bar is 300 µm.