Something new under the sun: Slippery surfaces, now transparent!
Sometimes it isn’t about what plants can directly do for us in terms of food, fuel or fiber. Instead it’s about how they inspire us. No, I’m not talking about Wordsworth’s daffodils or Frost’s birches. I’m talking about practical engineering. It turns out that the pitcher plants of genus Nepenthes have optimized the design principles behind the ultimate slippery surface. These carnivorous plants rely on this slipperiness to trap ants and other insects into their pitchers, which are filled with digestive juices. The way that pitcher plants create their slippery surface is distinct from current engineering strategies to develop non-stick surfaces. This so-called ‘bio-inspired’ engineering strategy applies nature’s principles to modern human problems.
The Aizenberg lab in Harvard’s Wyss Institute for Biologically Inspired Engineering has been pioneering this technology to develop improved liquid-resistant surfaces, called slippery liquid infused surfaces or SLIPS. Check out this video clip of Aizenberg describing SLIPS. Like the pitcher plants, a porous solid is used as the base structure, but a liquid lubricant is used as the filler creating a film at the surface. This film is responsible for kicking the slipperiness up a notch because the liquid-liquid interface created by the lubricant film works better as a repellent than a liquid-solid or liquid-air interface. For the past two decades, the majority of non-stick coating research has focused on materials that rely on a liquid-air interface.* The Aizenberg lab has studied the variables of the bio-inspired system and has reported methods to manufacture it as a material coating. Note, that while the fundamental idea was taken from nature, the actual coatings produced are not derived from pitcher plants. Still not impressed, check out this video:
The SLIPS technology has uses far beyond foiling vandals. As the mother of a small child, I spend quite a bit of time dealing with the effects of liquids being where they should not be. I would almost be willing to coat everything I own in SLIPS! No more grape juice absorbing into the car seat. No more syrup in the carpet. No more spaghetti sauce on the walls. You get the idea. Of course there are other uses beyond these everyday trivial annoyances. The SLIPS coating is potentially useful for uses as diverse as preventing ice build-up or bacterial growth on surfaces. Think de-icing planes, eliminating damaging ice formation on power lines, or creating sterile surfaces for medical purposes.
Am I the only one thinking about this possible application?
As if these possible applications weren’t exciting enough, the real news this week from the Aizenberg lab is that SLIPS is now more durable and available as a fully transparent coating. In a paper in Nature Communications, Vogel and co-authors describe the next version of SLIPS that makes the coating technology more versatile. The scratch-resistance and optical properties open more practical application possibilities from coating eyeglass lenses to solar panels to automobile windshields. No more defrosting required!** It seems the Aizenberg lab has optimized the SLIPS system for the right combination of physical properties as a proof of theory, but there is still work to be done to make it economical and manufacturable on a commercial scale.
So, thanks for the idea, plants!
*On a related note, the other liquid-repellents using liquid-air interface were based on lotus leaves. Apparently, plants are experts in non-stick technologies.
**Not that I worry about that too much down here in Louisiana, but still.
***One last observation purely from a science news standpoint- this story is a great example of an informative piece of news. The available press release and the Aizenberg lab website included specific details and references to primary peer-reviewed scientific literature (with convenient links to PDFs of the full texts) of how the technology works. If you want more details about the chemistry, physics and engineering behind SLIPS, please consult those sources.