We’ve discussed the creation of electronic plants recently and the idea of using plants as electrical storage and transferring devices, allowing an electric connection from, say, one end of a garden or field to another.

But plants can transfer far more than just electricity. They are already masters at transferring necessary nutrients from the soil up into their tissues using vast networks of roots. Some plants even survive by taking advantage of other root systems and stealing away nutrients for themselves.

One of the primary substances moved between the xylem, system that takes nutrients from the roots up into the tissues and leaves, and phloem, system that takes nutrients made via photosynthesis in the leaves down into the rest of the tissues, network is a simple one.


Passive Watering

The huge, hulking structures that plants are need a significant amount of water to keep up cellular function. Sure, their lack of movement or other activity reduces their needs significantly compared to constantly moving animals such as us, but the required amount of water remains significant.

The thing that makes this part of the xylen system special, however, is that it is not an active pumping system. Plants do not waste energy forcing water and nutrients up their piping. Instead, they have set up a passive diffusion system using mechanisms such as transpiration, pressure flow, and osmosis gradients.

All three work around differentials in pressure, whether from water evaporating from the top of the plant pulling up water from the lower tissues, to the lack of water in the roots forcibly using osmosis to pull in water from the soil, which also pushes the water inside the plant upward from the increased pressure from below.

Stealing From The Classics

It is these sorts of incredibly developed systems over evolutionary time that has amazed scientists in the field of microfluidics, which is the study and manipulation of water systems on the micro scale.

Using plant and especially tree systems as an inspiration, researchers from MIT and Cornell University have developed what they call a “tree-on-a-chip”. It works in the same way actual tree systems do, using passive osmotic pressure differentials to drive the water flow. Due to this, it requires no moving parts or active systems for pumping.

Though, as one would expect when working with a plant based system, passive pumping such as this is a slow process, but one that is still able to move a significant amount of water and other materials.

It has been suggested by researchers that one use for the chip is as an actuator to control a system in small-scale robots. A passive system will allow less weight, materials, and overall mechanical oversight than an active pumping or moving system. This is especially true due to the fact that making smaller and smaller moving parts becomes more and more prohibitively expensive, counter-intuitive as it may seem.

The Last Touch

The building of hydraulics-based robots is already a significant field of study, including at MIT itself. One of the primary researchers has had a focus on creating small-scale versions of hydraulics robots, but wanted to look into making simpler mechanical systems that required less money and effort. They would also be less likely to break as fast if there were less moving parts.

Previous attempts to make hydraulics systems using passive pressure diffusion similar to tree’s xylem processes did not turn out to be that effective, with the passive pumping running out of steam in only a few minutes. Comparatively, this new chip can work for several days before the pressure becomes no longer effective.

The key was to include a third part of the tree’s mechanisms, not just the xylem and phloem, but also the leaves’ sugar system as well. Sugars diffusing into the phloem increases the sugar to water ratio and maintains a stable osmotic pressure that offsets any incoming water.

Little Construction Needed

The chip itself is a plastic casing with two small channels that mimic the xylem and phloem systems. As you would find in a tree, the xylem was filled with water and the phloem with the sugar and water mixture to create a gradient. A semi-permeable material was placed in between the two channels, just like the cellular structures in between them in trees themselves.

Lastly, the special difference was added, with another semi-permeable membrane being placed on the phloem side and a sugar cube on top of it acting as the diffusor of sugars into the phloem system. Once water was connected up and added into the xylem side, the cycle was complete.

The chip was capable, for several days at least, of pulling water from the water source into itself and out into another container. And it was largely a simple creation once the idea for it was sparked.

With this completed, the next step is to actually build robots that will utilize it, though that may be a longer process. But, someday, this invention may help small-scale robots function in everyday life.

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Photo CCs: Emirgan 04589 from Wikimedia Commons

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