The power of today's electronic computing systems is not a point of debate. It is possible to crunch enormous volumes of data, run complex software and handle an array of tasks that would have once seemed unimaginable.
Yet, these systems are not ideal for many environments, and certain use cases. They require an electrical outlet or battery, and they can be cumbersome to control because they require an interface that must bridge the physical and electronic worlds.
As a result, bioengineers are exploring alternatives in the field of microfluidics. In June 2023, researchers at the University of California, Irvine (UC Irvine) and California State University, Long Beach (CSULB) reported a breakthrough in the journal Science Advances. They developed a pneumatic computer that uses pressure rather than electricity to encode and decode data on a lab-on-a-chip device.
"Microfluidics technology can drive significant advances in applications ranging from epidemiological testing to environmental monitoring and food safety," says Elliot Hui, an associate professor of biomedical engineering at UC Irvine and lead author of the paper.
The technology also has applications in soft robotics and medical prosthetics.
"Today's lab-on-a-chip systems must usually be accompanied by a large electromechanical apparatus to interface between electronic and fluidic components. We're looking to eliminate it," said Hui.
Adds William Grover, an associate professor in bioengineering at the University of California, Riverside, and a pioneer in the field of microfluidics, "These pneumatic systems take an age-old idea of computing without electricity and make it feasible for controlling a variety of advanced biological and chemical systems."
Computing Under Pressure
The idea of constructing computing devices that tap into fluidics systems is not new. Grover points out that over a century ago, player pianos used air to read songs that were punched in paper rolls. Various other computing systems have incorporated water, air, or other elements.
"Pneumatics has long been viewed as a viable way to compute. But as low-cost electronics emerged, the focus shifted mostly to building more powerful and inexpensive computing systems powered by electricity," Grover explains.
Today's lab-on-a-chip systems, used for tasks such as Covid tests or growing cell cultures—either have extremely limited onboard capabilities or rely on a separate computing device—often large, unwieldy, and costing tens of thousands of dollars—to control specific functions.
The system developed by the current group of researchers eliminates the need for any external device. "The significance of this device is that it not only can compute, but it can also control fluidic systems," explains Siavash Ahrar, an assistant professor in the Department of Biomedical Engineering at CSULB and a member of the research group. "We can manipulate air pressure to arrive at a desired outcome."
The research team developed a 0.25-millimeter-thick sheet of silicone and placed it between two thin panes of glass etched with tiny channels. Valves open and close by deflecting the silicone sheet—a process that mimics electronic transistors. Variations in pressure within the channels emulate the way conventional computers use voltage fluctuations to produce binary code.
In this case, a "1" represents vacuum pressure and a "0" is atmospheric pressure. By swapping tiny silicone sheets that function like punch cards, it's possible to build a full-fledged computing device that can be programmed. "This translates into a lab-on-a-chip system that is small, flexible, and potentially inexpensive," Hui says.
The Right Touch
The emergence of pneumatics as a computing tool could alter many fields and lead to new innovations. It would provide inexpensive testing methods for viruses, help monitor food safety, and detect environmental contaminants and pollutants. Moreover, it is possible to evolve beyond merely testing for the existence of a pathogen or particle, something today's testing kits already can do.
"By programming a device to perform dilutions, you can detect concentration levels, such as the viral load for a patient or the precise contamination level for a water or air sample," Ahrar says. "It's possible to obtain a much more detailed and accurate analysis at a much lower price."
Not only would standalone pneumatic logic deliver enormous diagnostic benefits in labs, hospitals, and environmental settings, but the technology enables lab-on-a-chip tests in places where they have never been available, Ahrar says. "This makes it possible to take clinical testing into the field—including in developing countries and other locations that have traditionally been excluded from testing."
Another space that could benefit from pneumatic computing is soft robotics and prosthetics, Ahrar says. These devices, typically constructed with silicone rubber, increasingly are used for rehabilitation and to work with children suffering from disabilities or trauma. Soft robots operate with pulses of pressure, typically generated by a computer connected to the device through a large number of valves and tubing.
Cutting cords and cables would reshape the way these devices are used. "Traditional systems are bulky and difficult to manage," Ahrar says. "A pneumatic device could change that. It would deliver all the functionality of a conventional computer on a standalone soft robot."
Constructing a commercially viable pneumatic computing device still faces headwinds. For example, the system developed by Hui and his team holds only four bits of data and has limited on-board circuitry and logic. As a result, it delivers only basic functionality. "There is still a considerable amount of work required to develop a fully functional system and manufacture devices at scale," Hui says.
Nevertheless, the researchers continue to experiment with different system configurations and incorporating three-dimensional (3D) printing into the design process, which could lead to more flexible and inexpensive systems. Pharmaceutical companies and others have expressed interest in the technology, which could help make current lab-on-a-chip systems far more powerful and flexible.
Grover says the technology could also make healthcare more efficient by letting hospitals reprogram medical devices for different uses, rather than requiring separate devices for everything. "Much the way a smartphone handles tasks that used to require separate dedicated devices, pneumatic logic could make it easier for one device to run different programs and perform different functions," he explains.
Concludes Hui: "Microfluidics offers a lot of intriguing possibilities."
Samuel Greengard is an author and journalist based in West Linn, OR, USA.
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