In the 1960s and 1970s, as engineers began to create the first computers, some people explored the idea of performing computations using fluids instead of electronics.  Known as fluidic computing, this idea fell from popularity relatively quickly because no one could miniaturize a control system capable of handling minute amounts of fluid.  Today, however, a few researchers such as Manu Prakesh, PhD, have realized that fluids and bubbles can be controlled by exploiting fluid dynamics.  This insight has led to the creation of new microfluidic tools that may someday be useful for high-throughput screening and compartmentalized chemistry.

Fluidic computing shows that it is possible to manipulate information and material at the same time.  Prakesh has created a number of droplet-based circuit elements that can be combined to perform complex computations.  Some examples of these circuit elements include logic gates, flip-flops, counters, ring oscillators, and synchronizers.  Prakesh has also written open source software to help fellow engineers design complex systems from the building blocks that he has created.  Because these computational circuits are easily shrinkable and depend on a pressure source instead of a power source, they might work well in implantable devices.

As part of his work, Prakesh has also studied the way in which natural organisms manipulate fluids.  One animal that he has studied is the red-necked phalarope, a shorebird that feeds on small aquatic organisms.  The red-necked phalarope has long bill and uses what is known as a capillary ratchet to coax water droplets up its bill.  The bird vibrates its bill so that water droplets drive themselves upward as they seek to minimize their surface area.  Learning from the phalarope’s behavior, engineers have now created microfluidic devices to move fluid droplets in similar ways.

Another example of an organism that carefully manipulates fluids is the water strider, an insect that walks on water.  The legs of the insect are covered with fine, hydrophobic hairs that usually repel water.  The water strider is able to generate traction because the hairs on its legs are oriented so as to form a directional adhesive.  In other words, the legs of the water strider only stick to the water’s surface when the legs are oriented in one direction.  Thus, the motion of a water strider can be divided into a striking phase and a gliding phase.  Engineers have been able to create surfaces similar to the legs on a water strider, and vibrating these surfaces causes water droplets to move in one direction only.             

Taken together, the recent advances that have been made in the handling of fluid droplets promise to help engineers build better implantable devices, perform more exact combinatorial chemistry, and conduct more efficient screening experiments.

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