Various microfluidic cell culture devices have been developed for in vitro cell studies because of their capabilities to reconstitute in vivo microenvironments. However, controlling flows in microfluidic devices is not straightforward due to the wide varieties of fluidic properties of biological samples. Currently, flow observations mainly depend on optical imaging and macro scale transducers, which usually require sophisticated instrumentation and are difficult to scale up. Without real time monitoring, the control of flows can only rely on theoretical calculations and numerical simulations. Consequently, these devices have difficulty in being broadly exploited in biological research. This paper reports a microfluidic device with embedded pressure sensors constructed using electrofluidic circuits, which are electrical circuits built by fluidic channels filled with ionic liquid. A microfluidic device culturing endothelial cells under various shear stress and hydrostatic pressure combinations is developed to demonstrate this concept. The device combines the concepts of electrofluidic circuits for pressure sensing, and an equivalent circuit model to design the cell culture channels. In the experiments, human umbilical vein endothelial cells (HUVECs) are cultured in the device with a continuous medium perfusion, which provides the combinatory mechanical stimulations, while the hydrostatic pressures are monitored in real time to ensure the desired culture conditions. The experimental results demonstrate the importance of real time pressure monitoring, and how both mechanical stimulations affect the HUVEC culture. This developed microfluidic device is simple, robust, and can be easily scaled up for high-throughput experiments. Furthermore, the device provides a practical platform for an in vitro cell culture under well-controlled and dynamic microenvironments.

Microfluidic technology plays an essential role in various lab on a chip devices due to its desired advantages. An automated microfluidic system integrated with actuators and sensors can further achieve better controllability. A number of microfluidic actuation schemes have been well developed. In contrast, most of the existing sensing methods still heavily rely on optical observations and external transducers, which have drawbacks including: costly instrumentation, professional operation, tedious interfacing, and difficulties of scaling up and further signal processing. This paper reports the concept of electrofluidic circuits - electrical circuits which are constructed using ionic liquid (IL)-filled fluidic channels. The developed electrofluidic circuits can be fabricated using a well-developed multi-layer soft lithography (MSL) process with polydimethylsiloxane (PDMS) microfluidic channels. Electrofluidic circuits allow seamless integration of pressure sensors with analog and digital operation functions into microfluidic systems and provide electrical readouts for further signal processing. In the experiments, the analog operation device is constructed based on electrofluidic Wheatstone bridge circuits with electrical outputs of the addition and subtraction results of the applied pressures. The digital operation (AND, OR, and XOR) devices are constructed using the electrofluidic pressure controlled switches, and output electrical signals of digital operations of the applied pressures. The experimental results demonstrate the designed functions for analog and digital operations of applied pressures are successfully achieved using the developed electrofluidic circuits, making them promising to develop integrated microfluidic systems with capabilities of precise pressure monitoring and further feedback control for advanced lab on a chip applications.