Technology Review: Synthetic Tree Hauls Water

A tree can transport water an amazing distance--from its roots, through a trunk up to 85 meters tall, and finally to its leaves, where the water evaporates. Now, scientists at Cornell University have created a microfluidic system to mimic that process. Their "synthetic tree" opens up a new way to move liquids over long distances without using mechanical pumps.

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created the synthetic tree out of a thin sheet of hydrogel, a material more commonly used to make contact lenses. They etched two networks of parallel channels into the hydrogel to represent the capillaries in a tree's root system as well as the ones in its leaves. They connected the two networks with a single channel representing the trunk of the tree.

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In a real tree, evaporation from the leaves is what pulls water up through the plant--a process known as transpiration.

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Stroock and Wheeler found that their system accurately mimics this transpiration process, pulling water through at strengths several times greater than those inside a real tree.

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Furthermore, because the water in a tree is under negative pressure--as if it were being sucked up through a straw--the water is in a metastable state, meaning it is between a liquid and a vapor. So the synthetic tree could also serve as a model system for studying liquids in this state.

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"In the case of liquid under negative pressure, it would tend to boil and become a vapor to relieve the negative pressure. But trees have managed to handle water in a metastable state very efficiently, so that's why this work is so nice."

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Stroock envisions that the synthetic tree system could be used to move liquids passively without needing mechanical pumps. In heat-transfer applications, it could cool small devices, like laptop computers, or larger ones, like vehicles, or even buildings. It could also be part of an soil remediation system, Stroock says. Instead of needing to flood soil with water to flush out contaminants, a synthetic tree could pull the contaminated water out.

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