Biochemical engineers at the University of California, Irvine, have developed a finite state machine (FSM) implemented as a pneumatic circuit using microfluidic valves to build a lab-on-a-chip.

For years, biochemical and mechanical engineers have been attempting to automate several of the chemical processes that are currently done by hand — for example, lab technicians using pipettes to determine the concentration of a chemical dissolved in a liquid. According to the researchers, automating these tasks could make them less expensive as well as expedite the time it takes to complete them, thereby potentially offering medical lab results in minutes instead of hours. As such, the engineers have been attempting to build a lab-on-a-chip, with help from pneumatics.

Autonomous control of serial dilution. (A) System-level diagram of the autonomous dilution ladder. A 4-bit FSM controls routing of peristaltic waveforms from the pump oscillator to the appropriate rungs of the dilution ladder. (B) Annotated image of microfluidic chip: FSM (box 1), dilution ladder (box 2), and ring oscillator (box 3). The pump control routing network makes up the remainder of the chip. (C) Time-lapse images of the 1:1 serial dilution process. Peristaltic pumping around each loop is driven by three valves actuated in a ripple pattern: one valve in the middle of a rung and another two on the far left and right. During each dilution step, additional unactuated valves along the far left and right seal off the rest of the rungs to create a closed loop between the two active rungs. The two smaller circles along each rung are not actuated but instead provide flexible windows to allow rung volume to expand and contract in response to peristalsis. Source: Science Advances (2023). DOI: 10.1126/sciadv.adg0201

Because several chemical processes involve the movement of liquids, the researchers investigated the use of water pressure instead of electricity when creating circuits for use on a possible lab-on-a-chip. Consequently, the team built a tiny sandwich featuring panes of glass as the bread and a sheet of silicone as the interior, or filling of the sandwich. Ahead of assembling the so-called sandwich, however, the researchers etched the glass panes to enable a liquid to pass through while holes poked into the silicone sheet connect the channels in the glass panes.

To stand in for the zeroes and ones used in FSMs, the researchers used pressure — wherein standard atmospheric pressure represented a zero and vacuum induced pressure represented a one. Meanwhile, the coding programs were achieved by poking holes in the silicone sheet.

The team then tested the structure by building a four-bit lab-on-a-chip, programmed to conduct serial dilution wherein the concentration of a chemical in a solution is determined. According to their findings, the team demonstrated that microfluidic devices similar to theirs could potentially be used for applications including testing blood not just for viruses like SARS-CoV-2, but also their concentrations.

A study detailing the research, Pneumatic computers for embedded control of microfluidics, appears in the journal Science Advances.