Engineers at MIT have successfully developed a microfluid device incorporating the pumping mechanism existing in plants with the intent to apply the device for moving small robots.

The "tree-on-a-chip" was a complete replica of the plan-based water pumping technology where no moving parts or external pumps are engaged. The MIT device showed that it can pump water and sugars for days at a constant flow rate.

Trees and plants are nature's superb hydraulic pumps. The internal hydraulic mechanism draws water from the leaves and pumps down the sugars produced by the leaves through photosynthesis into the roots. Water rises through tree channels like xylem abetted by surface tension.

The chip has smartly mimicked the channels that take water to the phloem. In trees, water travels up the xylem channel and moves into the phloem after being filtered through a semi-permeable membrane under a process called osmosis. From the phloem, water goes to the roots, enriched by nutrition that strengthens the roots.

The study has been published in the journal Nature.

Replicating Nature's Complexity

"The goal of this work is cheap complexity, like one sees in nature," noted Anette Hosoi, professor and associate department head for operations in MIT's Department of Mechanical Engineering.

Hosoi noted that adding another leaf or xylem channel in a tree is easy. But small robotics is marked by difficulty in many areas including manufacturing, integration, and actuation.

"If we could make the building blocks that enable cheap complexity, that would be super exciting. I think these [microfluidic pumps] are a step in that direction," she added.

The tree-on-a-chip device successfully overcomes the limitations of the half-baked attempts made in the past when microfluidic pumps used fabricated parts to ape xylem. In the past efforts, the hydraulic action would stop within a few minutes.

The MIT project was spurred by the need to design hydraulic robots on a smaller scale so that they perform like the bigger robots of Boston Dynamic's four-legged robot moved by hydraulic actuators.

Robot Applications

Considering the ease to make tree-on-a-chip, it is easier to integrate it into small robots to produce hydraulic functions and motions without any pumps or parts.

"If you design your robot in a smart way, you could absolutely stick a sugar cube on it and let it go," Hosoi said.

Critical Sugar Element

Credit for the success of the tree-on-a-chip device lies in the sugar element. The researchers perfected the hydraulic mechanism by simulating xylem and phloem channels through drilling of plastic slides.

Filling xylem with water, they separated xylem and phloem by a semi-permeable membrane and placed a sugar cube on top of the membrane to render the pressure for pulling down the enriched water to the roots.

The success of the chip in perfectly aping a plant's water pumping mechanism was amply demonstrated with the chip pumping water within itself and later to a beaker at consistent rates for so many days.