Tropical Plant Inspires Super-Slippery Coating for Medical Use

Chemical engineers have turned to exotic meat-eating plant life for inspiration in creating materials that have potential for use as a coating on medical devices.

The pitcher plant – which is carnivorous by trapping and digesting animals in leaves that resemble trumpets or small pitchers – has a highly slippery surface that stops its prey from escaping.

This surface can repel liquids and contaminants, the scientists from Harvard University found, and it has self-healing properties when scratched.

They mimicked these effects in their work to develop a transparent coating they call SLIPS (slippery liquid-infused porous surface), which has been recognized in the latest Institute of Chemical Engineers awards, shortlisted at the end of 2013.

First publishing their work in Nature, back in 2011, the researchers succeeded in furthering a decade of similar research that had used the lotus plant for inspiration, for its “natural non-wetting structures.”

While this progress in chemical engineering had inspired the development of liquid-repellent micro-textured surfaces, these were “still plagued with problems that restrict their practical applications,” including not being able to self-heal.

Medical tubing application

Nepenthes-Burkei - the carnivorous pitcher plant
The carnivorous pitcher plant, which is shaped like a small pitcher and has a slippery inner surface, has given scientists inspiration for a super-slippery coating for medical devices.

Taking inspiration from the pitcher plant’s inner surface to develop the properties of the new material, however, has meant that it could be used to coat the insides of medical tubing, such as catheters and blood transfusion systems, improving the flow and sterility of fluids through them.

The scientists created their super-slippery surface by infusing a “nano/micro-structured porous material” with a lubricating fluid.

They say their approach is not costly, being “applicable to various inexpensive, low-surface-energy structured materials (such as porous Teflon membrane).”

The chemical engineers list a number of remarkable properties to their new material, which can:

  • Repel various simple and complex liquids (water, hydrocarbons, crude oil and blood)
  • Quickly restore liquid-repellency after physical damage (in under 1 second)
  • Resist ice adhesion, and
  • Function at high pressures (up to about 680 atmospheres).

Commenting on the shortlisted innovation, Dr. David Brown, chief executive of the Institute of Chemical Engineers, says: “Some existing coatings have limitations, including contamination and degradation by contaminants, lack of self-healing capabilities and damage tolerance.”

Dr. Brown adds:

“By mimicking the pitcher plant’s skin structure, Harvard University’s new coating self-heals almost instantly, even if scraped with a knife or blade.

It is capable of operating in extreme temperatures and high pressure, and can be applied to surfaces ranging from metals and semiconductors, to paper and cotton fabric.”

BBC archive footage shows a short video about the pitcher plant. The particularly large example has 2-3 pints of digestive liquid in it and can trap small rodents – there is one record of a drowned rat being discovered within the plant’s modified leaf structure.

The video also shows, sped up by time-lapse photography, the growth of the carnivorous trap from what first appears to be a leaf shoot. The plant, the Nepenthes rajah, grows only in one region, a mountainous one in Borneo.

Carnivorous plant inspires protective coatings, statement from the Institution of Chemical Engineers media centre, published online, accessed January 2nd, 2014.

“Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity.” Wong T, Kang SH, Tang SKY, and others. Nature, 2011, volume 477, pages 443-447 (published online, September 21st, 2011; DOI:10.1038/nature10447). Abstract at Nature website.Full-text PDF at Harvard website.