Meeting 1

Paper: Minsoung Rhee and Mark A. Burns. 11/7/2009. “Microfluidic Pneumatic Logic Circuits and Digital Pneumatic Microprocessors for Integrated Microfluidic Systems.” Lab Chip, 9, 21, Pp. 3131–3143. Publisher's Version

Presenter: Elizabeth Gallardo, Louis de La Rochefoucauld

Background: Both presenters are from Professor Robert Wood’s Microrobotics Laboratory, which specializes in developing small robots. Most famously, the lab developed RoboBee, a tiny flying robot. The lab has recently ventured into the field of soft robotics. 

Elizabeth and Louis are interested in soft controllers and have been exploring microfluidics  to leverage microfluidic circuits as oscillators to drive soft robots. They believe that more applications can be achieved if digital logic systems in microfluidics can be adopted in the robotics field. Their long term goal is to build a roboticists-friendly library of microfluidic circuits to enable more applications. 

Therefore, Elizabeth and Louis presented the paper “Microfluidic Pneumatic Logic Circuits and Digital Pneumatic Microprocessors for Integrated Microfluidic Systems.” In this paper, the authors construct a basic binary valve system using negative pressure and a flexible membrane. When negative pressure is created using vacuum, the membrane, or diaphragm, is pulled and allows flow. When the vacuum is turned off, normal atmospheric pressure pushes the membrane back and closes the channel. 

Building on NOT gates constructed from these diaphragm valves, the authors present a few interesting circuits, including NOR gate(figure 4), NAND gate(figure 5), XOR gate (figure 5), pneumatic flip-flop that can be used to store binary data (figure 7), Pneumatic gated D latch (figure 8), shift register that consists of two D-latch (figure 9), 4-bit digital pneumatic microprocessor that controls four outputs (figure 10), 3-bit microprocessor that controls 8 outputs (figure 11).

In an attempt to recreate the devices in the paper for their lab uses, Elizabeth and Louis used quake valves. Different from the diaphragm valves, the quake valves are initially open and become closed with positive pressure, and they are also easier to manufacture and better to control with pressure. They use 3D printing for remodeling the circuits. However, the first two iterations produced unsatisfactory results due to 1) too much pressure loss in the channel 2) with wider channel and simplified circuit, pressure is still too weak to activate the valves.

Finally, Q&A discussions included possible extensions of current devices into larger circuit systems, ways to simulate resistance, capacitor and voltage divider in such devices like in electronic designs, comparison of electronics and microfluidics in terms of scalability, etc.