Tree-On-A-Chip Mimics Plants' Hydraulic Pumping Power

CC BY-NC-ND 3.0. MIT News

Trees and other plants are natural hydraulic pumps. They efficiently and continuously pull water up from the roots to the leaves and send sugars produced in the leaves back down. This natural phenomenon inspired engineers at MIT to make a device that mimics the hydraulic action of plants to power robots and other technology.

The so-called tree-on-a-chip has no moving parts or pumps and like a real tree is able to passively and continuously pump water and sugars through the chip. The device can maintain a steady flow rate for days.

What's the point of this device other than its cool factor? Well, engineers have found it difficult to tiny pumps and parts that can power the movements of tiny robots. This new technology could act as a mini hydraulic actuator for these small bots, propelling them with sugar power.

“For small systems, it’s often expensive to manufacture tiny moving pieces,” said Anette “Peko" Hosoi, professor and associate department head for operations in MIT’s Department of Mechanical Engineering. “So we thought, ‘What if we could make a small-scale hydraulic system that could generate large pressures, with no moving parts?’ And then we asked, ‘Does anything do this in nature?’ It turns out that trees do.”

In trees, the hydraulic system is made up of channels of tissues called xylem and phloem. The system balances itself. When there is more sugar in the phloem, more water is pulled up by the xylem to flush the sugar down to the roots to keep the sugar-to-water ratio in balance. The leaves also play a crucial role in keeping up a constant production of sugar, which keeps the flow of sugar and water steady through the tree.

The create this on a chip, the team combined two plastic slides and drilled two channels that act as the xylem and phloem. They inserted a semipermeable material between the channels like in the membrane in a tree and filled the xylem with water and the phloem with water and sugar. Another membrane was put over the phloem and then a sugar cube was placed on that to represent the leaves that deliver extra sugar. The chip was connected to a tube ran from a tank of water.

The chip was able to passively and constantly pump water from the tank through the chip and then out to a beaker at a steady rate for several days. This device could be built into small robots to hydraulically power movements without the need for moving parts or pumps. Even better, you could just put a sugar cube on top and off it'd go.