One Friday morning, Peter Parker and his biology classmates visited a research laboratory at a metropolitan university. Minutes after Peter stepped into the research laboratory, a genetically altered spider bit him. Within the following hours, Peter experienced changes in his body that gave him the ability to stick to walls and to shoot cobwebs. Peter transformed into Spider-Man.
Scientists predict that within the next 10 years this tale of science fiction will become a reality. Hopefully, humans will not have to suffer from a spider’s bite. Rather wear a suit made of a material with very strong adhesive properties.
Spiders and geckos are the inspiration for these adhesive materials. Geckos, the small brown or dark gray lizards, have a sticky pad on the sole of their feet that allow them to climb smooth surfaces and even walk on ceilings while upside down. These sticky pads allow geckos to hold up to 100 times their own weight. Evolution has been entrusted to develop pads with a high density of tiny hairs that interacts with the surface where the geckos walk on.
But, how does it work? Scientists want to understand the mechanism by which geckos’ feet adhere to any surface. Since the adhesion is dry, scientists know there are no chemicals involve in the adhesion process. It must be a purely physical attraction.
A study published by Eduard Arzt (PNAS, volume 102, page 16293), a scientist at the Max Planck Institute for Metals Research in Germany, and another study published by Kellar Autumn (PNAS, volume 99, page 12252), a professor at Lewis & Clark College in Oregon, have shown that two kind of attractive forces are responsible for the adhesive properties of geckos: capillary and van der Waals. The attractive forces between the tiny hairs and the surface work as a Velcro; that is to say, geckos’ feet stick and take off from any surface with ease.
The adhesive mechanism of spiders is similar to the one of geckos. Spiders also have tiny hairs on their feet that give them a strong dry adhesion. Van der Waals and nanointerlocking, also known as friction, are the two forces involve in the adhesion process of spiders.
Nicola M. Pugno, a professor at the Polytechnic University in Turin, Italy, is researching a synthetic material that will mimic the adhesion properties of spiders and geckos. In a paper published in Journal of Physics: Condensed Matter (volume 19, page 395001) professor Pugno proposed to use carbon-nanotube-based technology to develop the sticky material.
Carbon nanotubes are cylindrical carbon molecules whose diameter circles the nanometer. Hence, a carbon nanotube is very small; it is close to 1000 times thinner than a human hair.
Ali Dhinojwala, a professor in the department of polymer science at Akron University in Ohio, published a study in Chemical Communications (volume 30, page 3799) that shows how carbon nanotubes generate adhesive forces 200 times greater than those on the tiny hairs of geckos.
If a pair of “gecko-material gloves” can sustain a mass of 2552 lb (calculation presented on Pugno’s paper), then a pair of gloves made of a “carbon-nanotube-material” is the perfect complement to the Spider-Man’s suit.
Within the next 10 years, many other scientists around the world will continue to develop technologies with properties never seen before. The understanding and manipulation of organic and inorganic matter at the molecular level will give us a world possible only in science fiction. Who knows, maybe one of these days we will be able to stick to walls and to swing between skyscrapers, just like our hero: Spider-Man.
