If you're a regular reader of New Atlas, then you know that scientists enjoy putting things on chips. We've reported on a lung on a chip, a placenta on a chip, a kidney on a chip, and a heart on a chip – and that was in 2016 alone. Now, a team of MIT researchers has gone outside the human body in its chip enthusiasm and put an entire tree on a chip, sort of. The development could lead to improved hydraulics in tiny robots and maybe even allow them to be powered by simple sugar cubes.

Modeling elements from biology on chips allows scientists to run experiments, test out treatments and make observations that wouldn't necessarily be possible in other ways. The new chip from MIT allowed researchers to mimic the natural pumps inside trees. The device was able to move fluids without any external power source or mechanical parts for several days in the lab.


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Specifically, the chip mimics the tissue-filled channels in trees called xylem, which draw water up into a tree, and the other channels called phloem, in which sugar and nutrients are stored. Inside a tree, water travels up the xylem and is then drawn into the phloem through a semipermeable membrane through the process of osmosis. This water then washes down through the phloem, bringing nutrition to the roots.

Although researchers have developed such mini tree-based systems before, they always stopped pumping within minutes. That's because without a steady source of sugar, such as the one produced by the leaves of a tree, the fine balance between water and sugar that maintains osmosis is disrupted.

Sweet solution

To solve this problem, the MIT researchers simulated xylem and phloem channels by drilling into plastic slides. The xylem channel was filled with water, while the phloem channel contained water and sugar. The channels were separated by a semipermeable membrane. An additional membrane was placed over the phloem channel and a sugar cube was placed atop it to reproduce the sugar made by a tree's leaves during photosynthesis. The chip was then attached to a tube that allowed the system to draw water up from a tank.

Sure enough, the chip passively pumped water through itself and out into a beaker at a constant rate for several days.

While mimicking a tree on a chip seems like a fun thought experiment, the actual impetus for the project was to search for a way to develop hydraulic systems for small robots in an affordable way.

"The goal of this work is cheap complexity, like one sees in nature," said Anette Hosoi, professor and associate department head for operations in MIT's Department of Mechanical Engineering. "It's easy to add another leaf or xylem channel in a tree. In small robotics, everything is hard, from manufacturing, to integration, to 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."

Just how much of a step?

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

A paper detailing the work, which was sponsored in part by the US' Defense Advance Research Projects Agency (DARPA), has been published in the journal, Nature Plants.

Source: MIT News