When Abraham Stroock looks at a tree, he sees a complex feat of engineering. Inside the trunk, the branches, and the leaves, an intricate network of capillaries draws water dozens of meters into the air, with nary a pump in sight. This incredible system inspires Stroock’s approach to microfluidics.
Microfluidics involves moving tiny volumes of liquid through channels that are usually etched into a rigid material such as glass or silicon. Stroock, however, works with hydrogels, soft polymers that absorb water. Recently, he molded a capillary system that mimics a tree’s into a slab of hydrogel. This “synthetic tree” uses evaporation to pull water through its capillaries. The force it achieves is equivalent to that required to move liquid up a vertical column 85 meters high–the height of a redwood.
Liquid diffuses out of the hydrogel capillaries and into the surrounding material, just as it would in living tissue. Hydrogels are also biologically compatible, so such systems could serve as wound dressings that remove fluid and deliver drugs to promote healing. They could also act as three-dimensional scaffolds for engineered tissues; oxygen and nutrients could travel to cells inside the scaffolds. To mimic real tissues, the materials will ultimately have to provide conduits for proteins and cells–another step in Stroock’s plan to “give the material life.”