Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
, 99 (19), 12252-6

Evidence for Van Der Waals Adhesion in Gecko Setae

Affiliations
Comparative Study

Evidence for Van Der Waals Adhesion in Gecko Setae

Kellar Autumn et al. Proc Natl Acad Sci U S A.

Abstract

Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

Figures

Fig 1.
Fig 1.
Force of gecko setae on highly polarizable surfaces versus for surface hydrophobicity. (A) Wet adhesion prediction. (B) van der Waals prediction. (C) Results from toe on highly polarizable semiconductor wafer surfaces differing in hydrophobicity. (D) Results from single seta attaching to highly polarizable MEMS cantilevers differing in hydrophobicity. Note that geckos fail to adhere to hydrophobic, weakly polarizable surfaces [polytetrafluoroethylene where θ = 105° (25) and the dielectric constant, ɛ = 2.0 (23)]. Adhesion to hydrophilic and hydrophobic polarizable surfaces was similar. Therefore, we reject the hypothesis that wet, capillary interactions are necessary for gecko adhesion in favor of the van der Waals hypothesis.
Fig 2.
Fig 2.
Tokay gecko (Gekko gecko) adhering to molecularly smooth hydrophobic GaAs semiconductor. The strong adhesion between the hydrophobic surface of the gecko's toes and the hydrophobic GaAs surfaces demonstrates that the mechanism of adhesion in geckos is van der Waals force.
Fig 3.
Fig 3.
Synthetic gecko spatulae and perpendicular pull-off force measurements using a tipless AFM probe. Sample synthetic PDMS spatulae are shown in the Upper Left AFM tapping mode image of 16 × 12 × 1.72 μm3 scan area. Adhesive function of the synthetic was similar to that of natural gecko setae, suggesting that specific surface chemistry is not required, and that an array of small, simple structures can be an effective adhesive.

Similar articles

See all similar articles

Cited by 163 articles

See all "Cited by" articles

Publication types

LinkOut - more resources

Feedback