RESEARCH NEWS

SEPTEMBER 2009 | VOLUME 12 | NUMBER 9 11

Two scientists have discovered that the ability of

the gecko to grip onto smooth surfaces is actually

triggered by gravity, and that it is the steepness of

a surface that makes them deploy their gripping

mechanism. These findings and future results may

have applications in the medical world, space travel,

and in robotics, to name but a few.

The researchers, from the University of Calgary and

Clemson University, have been examining how and

when geckos use their specialized toepads to attach to

surfaces under different circumstances.

Published in the online edition of the Proceedings of

the Royal Society [DOI: 10.1098/rspb.2009.0946], the

research showed that the adhesive system was turned

on when a surface was inclined to at least 10 degrees,

regardless of the type of surface involved.

It was known how geckos are able to stick to most

surfaces but not what actually triggered the use of

the adhesion system. The setae, the bristles that cover

their toes, and the microscopic, hair-like filaments

called spatulae that are attached to them, give the

geckos the ability to grip, but it is also crucial that

they are able to turn the adhesion system on and off

easily as they move across a surface.

An interest in evolutionary biology and how animals

respond to particular challenges led the researchers to

explore how natural selection has created an system

that enables geckos to deploy their special grip when

needed.

A key insight of their research was in showing the

importance of feedback and perception for the

gecko, when it was realised that geckos never use

their clinging mechanism when on the horizontal,

even when that surface is extremely slippery. Russell

explains that “it may be disadvantageous for geckos

to use their adhesive system on level surfaces. We

know that it would slow them down, but we don’t

know if there are other physical limitations that would

render such a system less effective if not assisted by

gravitational loading that can be experienced in body

orientations beyond the horizontal.”

The hope is that an understanding of the geckos’

in-built traction system will have commercial

potential, from a use in space exploration, to military

applications such as in bomb disposal, to medical uses

such as bandages, or even in the area of robotics.

As Higham points out, “a robot could potentially be

faster when moving on a level surface by not adhering.

When the robot encounters an incline, it could then

deploy the system and climb.”

Russell and Higham now aim to continue by observing

different types, sizes and ages of gecko, to see how the

adhesive system is deployed in other species of geckos,

which will help them better understand the extensive

diversity of such systems.

Laurie Donaldson

Climbing the walls – gecko-styleBIOMATERIALS

Engineers have developed a new method for creating high-performance membranes from crystal sieves called zeolites; the method could increase the energy efficiency of chemical separations up to 50 times over conventional methods and enable higher production rates.Researchers led by chemical engineer Michael Tsapatsis of the University of Minnesota [Choi et al., DOI: 10.1126/science.1176095] reported this discovery in the July 31, 2009, issue of Science. Tsapatsis’s team developed a rapid heating treatment to remove structural defects in zeolite membranes that limit their performance, a problem that has plagued the technology for decades. This discovery could increase the energy efficiency of producing important chemical solvents for example; renewable biofuels such as ethanol and butanol.Conventional methods of creating zeolite membranes involves growing a film of crystals with small organic ions added to direct the crystal structure and pore size; two zeolite properties that help determine which molecules can pass through the material. Then they slowly heat the zeolite film in a process called

calcination to decompose the ions and open the pores. This method for creating zeolite films often leaves cracks at the boundaries between grains of zeolite crystals.In an effort to minimize the formation of cracks and other defects, the heating rate during calcination must be very gentle, extending the length of the process to well over 40 hours.Tsapatsis’s team developed a treatment called Rapid Thermal Processing (RTP), a treatment in which zeolite film is heated to 700 degrees Celsius within one minute and kept at that

temperature for no more than two minutes. Acting as an annealing method, RTP refines the granular structure of the zeolite crystal film.When the researchers examined the RTP-treated films they found no evidence of cracks at grain boundaries. Although they found other types of defects, these don’t seem to affect the membrane properties or performance.In a comparison to conventionally-made zeolite membranes, Tsapatsis said, “We observed a dramatic improvement in the separation performance of the RTP-treated membranes.” A second round of RTP treatment improved separation performance even further to a level on par with current industry separation methods.The researchers demonstrated the RTP process on relatively thick (several micrometers) zeolite membranes. Tsapatsis and collaborators are now working towards making zeolite membranes 10 to 100 times thinner to allow molecules to pass through more quickly. They hope to eventually implement RTP treatment with its beneficial effects to these membranes as well.Jonathan Agbenyega

Membrane breaks through performance barrierSURFACE SCIENCE

Membranes + defects (top), after RTP – defects (below).

Figure of a Gecko

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