“Sticking” with the Gecko

Van der Waals Forces and Animal Adhesion

upload.wikimedia.org http://www.gotpetsonline.com/pictures-gallery/reptile-pictures-breeders-babies/tokay-gecko-pictures-breeders-babies/pictures/tokay-gecko-0005.jpg

www.whyfiles.com

Activity Goal

• Explain how geckos and jumping spiders use van der Waals forces to adhere to surfaces

• Explain the relationship between mass of an organism and number of setae/100 mm2

• List some potential applications that use gecko/jumping spider adhesion properties

Terms to Know

• Micro symbol: mdefinition: one millionth or 10-6

• Micrometer or micronsymbol: mmdefinition: one millionth of a metera human hair is about 50 mm wide

http://images.google.com/imgres?imgurl=http://www.nsf.gov/od/lpa/news/03/images/wire_on_hair_big.jpg&imgrefurl=http://www.nsf.gov/od/lpa/news/03/pr03147_images.htm&h=960&w=1228&sz=197&hl=en&start=3&sig2=rkwzYL2bDxq6t_bdIfOY-Q&um=1&tbnid=Y9V-_MzcLrD-RM:&tbnh=117&tbnw=150&ei=EvDfR-zxI4_eigGbwcTUBQ&prev=/images%3Fq%3Dhuman%2Bhair%2B%26um%3D1%26hl%3Den%26rlz%3D1T4GGLJ_enUS248US253

Terms to Know• Nano

symbol: ndefinition one billionth or 10-9

• Nanometerone billionth of a meter

http://microcosm.web.cern.ch

0.1 nm 1-10 nm 1 m

10 m

100 m1 mm1 cm

The Nanoworld

• Nanotechnologythe control of shape and size at the nanoscale to design and produce structures, devices, and systems

Terms to Know

Terms to Know

• INTERmolecular Forces – Weak forces of attraction between

molecules (i.e. dispersion, dipole-dipole, dipole-induced dipole, hydrogen bonds)

– Much weaker than intramolecular forces

• Van der Waals Forces– Forces that arise when a temporary

dipole in a non-polar molecule induces a dipole in an adjacent non-polar molecule

d-

d+d-

+d

Terms to Know

Tokay Gecko (Gekko gecko)

an insect-eating, noisy reptile from South East Asia • Scansors

lamellae or gill-like structures on the bottom of the foot• Setae

hair-like bristles that come out of the scansors• Spatula

branches from the setae that end in flat triangles

http://en.wikipedia.org/wiki/Tokay_gecko

Gecko Morphology

http://images.google.com/imgres?imgurl=http://ist-socrates.berkeley.edu/~peattiea/gecko_foot_tour.jpg&imgrefurl=http://socrates.berkeley.edu/~peattiea/research_main.html&h=365&w=578&sz=77&hl=en&start=13&sig2=4K8MfL4Nukg2ujB4fltpEw&um=1&tbnid=F98wzSz5PBo28M:&tbnh=85&tbnw=134&ei=CfXfR-bxLpiCiAGXrfzDBQ&prev=/images%3Fq%3Dgecko%2Bsetae%26um%3D1%26hl%3Den%26rlz%3D1T4GGLJ_enUS248US253

Terms to Know

Jumping Spider (Evarcha arcuata)- a species of jumping spider primarily found in Europe• Scopula

protrusion found at the tip of each foot • Setae

hair-like bristles that come out of the scopulae • Setules

densely cover the setae and broaden into flat, triangular end

http://whyfiles.org/shorties/152sticky_spider/Photo courtesy Ed Nieuwenhuys

Getting a Grip on Spider Attachment: an AFM Approach to Microstructure Adhesion in Arthropods

Antonia B Kesel, Andrew Martin, Tobias Seidl

a) Tarsal claws, scopula and hairs

b) Scopulas differentiation into setae

c) Single setae covered with setules

d) Setule density is lower on upperside of the setae

e) Setules on the underside broaden to a flat, triangluar end

f) The spider’s elements that are in direct contact with the substrate

Station 1—Graph InterpretationArzt, Eduard, Stanislav Gorb, and Ralph SpolenakProc Natl Acad Sci U S A. 2003 September 16; 100(19): 10603–10606. Published online 2003 September 5. doi: 10.1073/pnas.1534701100. Copyright © 2003, The National Academy of Sciences

Q: What do each of the colored regions represent?

Q: What happens to the number of setae per 100 mm2 as the mass of the organism increases?

Q: What kind of relationship is this?

flies

beetles

lizards

bugs

spiders

Station 1—Graph InterpretationArzt, Eduard, Stanislav Gorb, and Ralph SpolenakProc Natl Acad Sci U S A. 2003 September 16; 100(19): 10603–10606. Published online 2003 September 5. doi: 10.1073/pnas.1534701100. Copyright © 2003, The National Academy of Sciences

The following pictures are Scanning Electron Microscope pictures of an animal’s foot. Match each picture with the correct organism: beetle, fly, spider, lizard

flies

beetles

lizards

bugs

spiders

beetlesflies spiderslizards

Station 2—ExperimentHow does the number of setae affect the strength of the

attachment force?

# of “setae” 4 8 16 32

Total Force (N)

Mass chosen to weight down toothbrush _________________Surface chosen __________________

Station 3—Applications/Biomimetics

• 2 Articles for students to read about newly designed gecko-tape.

• http://www.scientificamerican.com/article.cfm?id=gecko-inspired-adhesive-s “Gecko-Inspired Adhesive Sticks It to Traditional Tape”

• http://www.sciencedaily.com/releases/2012/02/120216165500.htm “Gecko Feet Inspire Amazing Glue That Can Hold 700 Pounds On Smooth Wall”

Station 3—Applications/Biomimetics

• 2 Articles cont.

• Answer questions relating to:– Advantages gecko tape might have over conventional tape– Problems in the manufacturing and use of gecko tape– Distance of setae to substrate

(nanometer scale)– Methods of adhesion in the gecko

(van der Waals forces)– Gecko and spider feet morphology

More Recent Developments

http://www.lclark.edu/~autumn/dept/Blog/4FB9A0EB-5911-4000-9D05-B1048F01E6C9.html

http://web.mit.edu/newsoffice/2008/adhesive-0218.html

Stanford University’s Sticky Bot

MIT’s dissolvable medical adhesive

Station 4—SEM ImagesStudents study SEM Images, read, and answer questions about gecko and spider morphology

Jumping Spider

Why do geckos/spiders have so many setae?they may not all have the correct orientation

How do they detach?their setae need to be at an angle greater than 30o

If all of a gecko’s setae were stuck to a surface at the same time, how many pounds would it be able to support? 286 lbs!

Why do pictures “c” & “d” for the Jumping spider look different? the bottom of the setae has a lot more setules than the

top

Gecko

What is the advantage to having flat ends?greater surface area

flies

beetles

lizards

bugs

spiders

Station 5 — Spider Student?

y = m (x) + blog (NA) = 0.699 log (m) + 13.8

How many setae/100 mm2 a 130 lb person would need to stick to a wall?

The equation for the best-fit line on the graph can be written: 

log of log of setae per 100 mm2 log of mass of organism in grams How many setae/100 mm2 would a 130 lb person need to stick to a wall? 1st: Convert 130 lbs to grams. mass = 59090 g   2nd: Substitute this value into the equation of the straight line.

  NA = 1.37 X 1017setae/100 mm2  

3rd: Convert this to setae / 100 cm2

  NA = 1.37 X 1023 setae / 100 cm2

+

+

13.8log(m)0.699=log(NA)

bxm=y

+= 13.8log(59090)0.699log(NA)

References:

Gecko pic- http://images.iop.org/objects/phw/news/12/10/14/Gecko.jpgGecko pic 2- http://www.exoticpetswholesale.com/i//sm_blue_gecko02.jpgTooth brush pic - http://www.kosherimage.com/images/tbrush-4layflat.jpgSpring scale pic- http://www.enasco.com/prod/images/products/2A/VC131047l.jpg

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