Featured Research

from universities, journals, and other organizations

How stick insects honed friction to grip without sticking

Date:
February 19, 2014
Source:
University of Cambridge
Summary:
When they’re not hanging upside down, stick insects don’t need to stick. In fact, when moving upright, sticking would be a hindrance: so much extra effort required to ‘unstick’ again with every step.

Scanning electron microscopy image of conical, micrometre-sized outgrowths that cover the tarsal ‘heel pads’ of some stick insects (false colours).
Credit: Image by David Labonte & Adam Robinson.

When they're not hanging upside down, stick insects don't need to stick. In fact, when moving upright, sticking would be a hindrance: so much extra effort required to 'unstick' again with every step.

Latest research from Cambridge's Department of Zoology shows that stick insects have specialised pads on their legs designed to produce large amounts of friction with very little pressure. When upright, stick insects aren't sticking at all, but harnessing powerful friction to ensure they grip firmly without the need to unglue themselves from the ground when they move.

In a previous study last year, the team discovered that stick insects have two distinct types of 'attachment footpads' -- the adhesive 'toe pads' at the end of the legs, which are sticky, and the 'heel pads', which are not sticky at all. The insect uses different pads depending on direction and terrain.

By studying the 'heel pads' in more detail, researchers discovered the insects have developed a way to generate massive friction when walking upright. They do this through a system of tiny hairs that use combinations of height and curvature to create a 'hierarchy' of grip, with the slightest pressure generating very strong friction -- allowing stick insects to grip but not stick.

The researchers say the study -- published today in the Journal of the Royal Society Interface -- reveals yet another example of natural engineering successfully combining "desirable but seemingly contradictory properties of human-made materials" -- namely, the best of both hard and soft materials -- simply through clever structural design.

"Just by arrangement and morphology, nature teaches us that good design means we can combine the properties of hard and soft materials, making elemental forces like friction go a very long way with just a small amount of pressure," said David Labonte, lead researcher from the Department of Zoology.

The power of friction relies on 'contact area', the amount of close contact between surfaces. In rigid materials, such as steel, even the tiniest amount of surface roughness means there is actually relatively little 'contact area' when pressed against other surfaces -- so any amount of friction is very small.

On the other hand, soft materials achieve a lot of contact with surfaces, but -- due to the larger amount of contact area -- there is also a certain amount of adhesion or 'stick' not there with hard materials.

To solve this, stick insect's hairy friction pads employ three main tricks to allow contact area to increase quickly under pressure, creating a scale or 'hierarchy' of grip with absolutely no stick:

  • Both the pad itself and the tips of the hairs are rounded. This means that, when pressure is applied, more contact area is generated -- like pushing down on a rubber ball.
  • Some hairs are shorter than others, so the more pressure, the more hairs come into contact with the surface.
  • When even more pressure is applied, some of the hairs bend over and make side contact -- greatly increasing contact area with very little extra force.

These design features work in harmony to generate large amounts of friction with comparatively tiny amounts of pressure from the insect. Importantly, there is hardly any contact area without some tiny amount of pressure -- which means that the specialised 'frictional hairs' don't stick.

Arrays of tiny hairs have been found before, for example on the feet of geckos, beetles and flies. However, these hairs are designed to stick, and are used when creatures are vertical or hanging upside down.

Sticky hairs are completely aligned and have flat tips -- meaning that they immediately make full contact that hardly changes with additional weight -- as opposed to friction hairs, with their higgledy-piggledy height ranges and rounded tips.

"We investigate these insects to try and understand biological systems, but lessons from nature such as this might also be useful for inspiring new approaches in human-made devices," said Labonte.

He uses the example of a running shoe as a possible human-made item that could be enhanced by stick insect engineering: "If you run, you don't want your feet to stick to the ground, but you also want to make sure you don't slip."

Adds Labonte: "Stickiness is the force that is needed to overcome when trying to detach one thing from another. If the soles of your feet were made of Scotch tape, it may be helpful when you are walking up walls or hanging upside down, but the rest of the time it would be incredibly frustrating."

"Stick insects have developed an ingenious way of overcoming the conflict between attachment and locomotion, with a dual pad system that alternates between stick and grip depending on the situation."


Story Source:

The above story is based on materials provided by University of Cambridge. The original story is licensed under a Creative Commons Licence. Note: Materials may be edited for content and length.


Journal Reference:

  1. D. Labonte, J. A. Williams, W. Federle. Surface contact and design of fibrillar 'friction pads' in stick insects (Carausius morosus): mechanisms for large friction coefficients and negligible adhesion. Journal of The Royal Society Interface, 2014; 11 (94): 20140034 DOI: 10.1098/%u200Brsif.2014.0034

Cite This Page:

University of Cambridge. "How stick insects honed friction to grip without sticking." ScienceDaily. ScienceDaily, 19 February 2014. <www.sciencedaily.com/releases/2014/02/140219075446.htm>.
University of Cambridge. (2014, February 19). How stick insects honed friction to grip without sticking. ScienceDaily. Retrieved September 23, 2014 from www.sciencedaily.com/releases/2014/02/140219075446.htm
University of Cambridge. "How stick insects honed friction to grip without sticking." ScienceDaily. www.sciencedaily.com/releases/2014/02/140219075446.htm (accessed September 23, 2014).

Share This



More Plants & Animals News

Tuesday, September 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Ice Age Wooly Mammoth Remains for Sale

Raw: Ice Age Wooly Mammoth Remains for Sale

AP (Sep. 23, 2014) A rare, well-preserved skeleton of a woolly mammoth is going on sale at Summers Place Auctions hope the 11.5-foot tall, almost intact specimen will fetch between $245,000 to $409,000. (Sept. 23) Video provided by AP
Powered by NewsLook.com
Fox Bites Conn. Student And School Staffers In Rare Attack

Fox Bites Conn. Student And School Staffers In Rare Attack

Newsy (Sep. 23, 2014) A fox attacked a second-grade boy at a Connecticut elementary school Monday. It also attacked two school staff members and a woman and her dog. Video provided by Newsy
Powered by NewsLook.com
Will Living Glue Be A Thing?

Will Living Glue Be A Thing?

Newsy (Sep. 23, 2014) Using proteins derived from mussels, engineers at MIT have made a supersticky underwater adhesive. They're now looking to make "living glue." Video provided by Newsy
Powered by NewsLook.com
Raw: Tiger Kills Man at India Zoo

Raw: Tiger Kills Man at India Zoo

AP (Sep. 23, 2014) A white tiger killed a young man who climbed over a fence at the New Delhi zoo and jumped into the animal's enclosure on Tuesday, a spokesman said. (Sept. 23) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins