Fig. 6.

Responses of the flow controllers for liquid flow, airflow, and vacuum level. Figures a and d show a settling time of 4.5 s and a resolution of 0.6 $\mathrm{\mu }$L min${}^{-1}$ respectively for the flow controller with liquid flow. Figures b and e show a settling time of 14 s and a resolution of 0.2 mL min${}^{-1}$ respectively for the flow controller with airflow. Figures c and f show a settling time of 2 s a resolution of 3 mbar respectively for the flow controller used to generate the desired vacuum. The black lines represent the applied voltage levels (shown on the right side of the y-axes) to the controllers, while the red lines are the system responses (shown on the left side of the y-axes). The dashed lines represent that the settling times are defined as the result reaches within 2 % of the desired stable values. These values are suitable for a lung-on-a-chip experiment parameters described in Table 2. The noise seen in Fig 6d-f is due to 8-bit ADC. It can be improved by using higher bit ADC or averaging the data. According to the manufacturer, the accuracy of the mass flow controller is $0.167\mathrm{\mu }\text{L}{\text{min}}^{-1}$ for water and $0.13\mathrm{\mu }\text{L}{\text{min}}^{-1}$ for air, and of the pressure controller is $0.075\text{bar}$ for air