Trees passively pull fluids great distances. Image Source: Flickr User: andrewmalone

As technology advances, it feels like there is a persistent desire to decrease size. Sleek cell phones over clunky landlines, minuscule video cameras over yesterday’s behemoth camcorders. But this emphasis on size can cause a number of issues for the scientists. In robotics, development is being stymied by the need for better (and smaller) hydraulic systems. It is often difficult to manufacture tiny moving pieces for robots, so researchers are seeking out ways to alleviate the need for moving parts altogether. As in so many things, they’ve turned to nature for a potential solution. Plants, from lavender to poplar trees, use a passive fluid transport system for a constant stream of nutrients.

In recently published research, scientists created a tree-on-a-chip in hopes of using this technique for microfluidics in finer movements in robots.1 This publication reveals that researchers were able to create a passive system that maintains a steady flow rate of water and sugars through the chip for several days. In conjunction with innovative lab software, this research can be refined and moved from the benchtop to the consumer.

Passive Transport at Its Finest

House plants like that immortal spider plant at my parent’s house all the way up to the tallest tree on earth, a 115.7 m tall redwood named “Hyperion”2, use the same fluid transport system. Phloem and xylem are the tissue systems responsible for their fluid and nutrient transport. Xylem is chiefly responsible for water transport, whereas phloem is the system that transports sugar and other nutrients around the organism. These two tissues work in tandem with the aid of basic water properties:

  • Cohesion-Tension – Water is cohesive, which aids in its desire to evade gravity. Water saturates cellulose microfibrils of the primary cell wall in mesophyll cells, cells which are also exposed to internal air space. Some water evaporates into the internal air pocket, decreasing the water on the mesophyll cell walls. This increases the tension on the water in the cells, thereby increasing the pull on the water within the xylem. Voila! This creates enough tension to draw water from the roots to the top of the tree and tips of the branches.3
  • Osmosis –  As sucrose, the product of photosynthesis, is actively transported from the source to the phloem, water potential in the phloem reduces. This causes water to move across a semipermeable membrane from the parallel xylem tissue. Increased water in the phloem drives the transport of sugars to sink cells (roots, fruits), where water may move back across the membrane into the xylem.4 This consistent overturn of water also contributes to water draw from roots to leaves.

Nature has done a superb job of creating a semipermeable system to drive fluid transport within plants, and similar membranes can now be modeled and designed using modern lab software. Osmosis is a natural process based on concentration gradients, but creating or assessing membranes to operate in passive hydraulics for robots is a more complicated avenue of investigation. Pore size, solute and pressure will need to be evaluated and modeled to ensure a consistent passive flow of adequate force to drive robotic movement.

Fueled by Sugar

Previous attempts at phloem/xylem systems of passive transport, regardless of scale, often ceased to function after a very short period of time. When reflecting upon these past failures, researchers identified the missing piece: the consistent sugar production of the leaves. The consistent drive to allocate recently produced sugar to sugar sinks is a large component of passive fluid transport in plants that most manufactured systems failed to incorporate.

When constructing this chip, the researchers sandwiched gaskets, channels and membranes. Using PVC and PET sheets, phloem and xylem channels were crafted, with a membrane in between and additional space for the phloem channel to interact with a sugar source. Now, the pièce de résistance: the investigators simply placed a cube of sugar over the phloem and they were off to the races! Constantly diffusing sugar into the constructed system mimicked leaves well enough to drive passive fluid movement for several days; an incredible achievement.

This preliminary research is still a far cry from its intended applications in robots. Researchers will need to determine exactly what solutes can be used with which membranes, a process which will benefit from modern lab software. By conducting in silico analyses and simulations, you can catapult your research into the future and move this novel information from benchtop to client base. BIOVIA Materials Studio is the missing key to rapidly advancing your research in this field. With extensive bottom-up computer simulations, you can save you and your lab both time and R&D funds that would otherwise be spent exploring dead ends. Please contact us today to learn more about how our software options can support the efforts of your lab.

 

  1. “Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip,” March 20, 2017, https://www.nature.com/articles/nplants201732
  2. “What is the World’s Tallest Tree?” April 15, 2013, http://www.livescience.com/28729-tallest-tree-in-world.html
  3. Movement of Water and Minerals in the Xylem,” Retrieved May 2, 2017 from Boundless Biology, https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/transport-of-water-and-solutes-in-plants-183/movement-of-water-and-minerals-in-the-xylem-698-11923/
  4. Movement of Water and Minerals in the Xylem,” Retrieved May 2, 2017 from Boundless Biology, https://www.boundless.com/biology/textbooks/boundless-biology-textbook/plant-form-and-physiology-30/transport-of-water-and-solutes-in-plants-183/movement-of-water-and-minerals-in-the-xylem-698-11923/