Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Absorption Hypothesis: Attachment of Beetles to Nanoporous Substrates
Elena Gorb 1 *, Solveig Kleinz 1 and Stanislav Gorb 1
1 Department of Functional Morphology and Biomechanics, Zoological Institute, University of Kiel, 24098 Kiel, Germany
Abstract-Traction experiments with ladybird beetles showed that forces on nanoporous substrates were significantly lower t hat those on solid
surface samples. The comparison of the evolution in contact angles of the two fluids, polar water and non-polar mineral oil, showed that porous
substrates absorbed both polar and non-polar fluids, whereas solid surface samples did not. Thus, the reduction of insect attachment on
nanoporous surfaces may be explained by (1) the absorption of the secretion fluid from insect adhesive pads by porous media and/or (2) the
effect of surface roughness.
It has been repeatedly reported that micro- and
nanostructured waxy surfaces of plants strongly reduce insect
attachment. To explain anti-adhesive properties of such
substrates, four hypotheses have been previously proposed: (a)
roughness hypothesis; (b) contamination hypothesis; (c) fluid
absorption hypothesis; and (d) wax dissolving hypothesis [1].
Recently, only the two first hypotheses ([2 – 6] for (a) and [7 –
9] fo r (b)) were proven. To date, the wax d issolving
hypothesis and the fluid absorption hypothesis have not been
experimentally tested. In the present study, we used
nanoporous substrates with the same pore diameter (220 – 235
nm), but different porosity (area of voids in a material surface,
normalized over the total area), in order to test the fluid
absorption hypothesis, claiming that the structured wax
coverage of plants may absorb the fluid from the setal surface
of insect adhesive pads and by this reduce the adhesion force.
We performed traction force measurements with tethered
seven-spotted ladybird beetles Coccinella septempunctata L.
(Coleoptera, Coccinellidae), walking on five different
substrates [10]: (1) smooth glass plate; (2) smooth solid Al 2 O 3
(sapphire) disc; (3 – 5) three types of nanoporous Al 2 O 3 discs
(back side of anodisc membranes Whatman, Schleicher and
Schuell, Whatman International Ltd., Maidstone, UK) having
the porosity of 28, 42 and 51%. Forces were measured with a
load cell force transducer (10g capacity, Biopac Systems Ltd.,
Santa Barbara, CA, USA). Both males (n=10) and females
(n=10) were used in the experiments.
We found that the forces ranged from 0.16 to 16.59 mN in
males and from 0.32 to 8.99 mN in females. The highest force
values were obtained on the smooth surfaces, where males
generated considerably higher forces compared to females. On
all three porous substrates, the forces were significantly
reduced, and the only difference was obtained between
nanoporous membranes having the highest and lowest
porosity. Males produced essentially lower forces than
females on porous samples [10].
The reduction of insect attachment on nanoporous
substrates may be explained by (1) possible absorption of the
secretory fluid from insect pads by porous media and (2)
surface roughness, reducing real contact area between tenent
setae of insect adhesive pads and substrate.
To examine the ability of porous substrates to absorb fluids,
we performed additional absorption experiments with solid
and nanoporous surfaces samples using a high-speed optical
contact angle measuring device OCAH 200 (DataPhysics
Instruments GmbH, Filderstadt, Germany). The comparison of
the evolution in contact angles of the two fluids, polar water
and non-polar mineral oil (Mobil DTE Medium, viscosity 43.4
mm 2 •s at 40°C [11]), showed that porous substrates absorbed
both polar and non-polar fluids (figure), whereas solid surface
samples did not. Since the beetle secretion or at least a part of
it consists of oily substances, we can conclude that adhesion
reduction in our traction experiments at least partially can be
explained by the ability of nanoporous substrates to adsorb
non-polar lipid-like fluids.
contact angle [ ° ]
70
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0
0 10 20 30 40 50 60
30
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absorption
absorption
0
0 10 20 30 40 50 60
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(a)
(b)
Figure 1. The evolution in contact angles of water (a) and oil (b)
on the nanoporous surface sample with the porosity of 42%.
This work was partially supported by the SPP 1420 priority
program of the German Science Foundation (DFG)
“Biomimetic Materials Research: Functionality by
Hierarchical Structuring of Materials” (project GO 995/9-1).
The first author thanks Naoe Hosoda (NIMS, Tsukuba, Japan)
for fruitful discussions.
*Corresponding author: egorb@zoologie.uni-kiel.de
[1] E.V. Gorb and S.N. Gorb, Entomol. Exp. Appl. 105, 13 (2002).
[21] S. Gorb, Attachment devices of insect cuticle (2001).
[3] A. Peressadko and S. Gorb, Proc. 1st Int. Conf. Bionik, 257
(2004).
[41] D. Voi gt et al., J. Insect Physiol. 54, 765 (2008).
[51] E. Gorb and S. Gorb, Entomol. Exp. Appl. 130, 222 (2009).
[6] J. M. Bullock and W. Federle, J. Exp. Biol. 212, 1876 (2009).
[7] L. Gaume et al., Arthropod Structure & Development 33, 103
(2004).
[8] E. Gorb et al., J. Exp. Biol. 208, 4651 (2005).
[9] E. Gorb and S. Gorb, Ecology and biomechanics: A mechanical
approach to the ecology of animals and plants, 147 (2006).
[10] E. Gorb et al., Proc. 9th Biennial ASME Conf. on ESDA, 1
(2008).
[11] M. Varenberg and S. Gorb, Adv. Mater. 21, 483 (2009).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 208