Biomedical Engineering Reference
In-Depth Information
complex micro- and nanoscale surface architec-
ture that minimizes adhesion and results in the
lotus leaf's ability to pick up dirt in water drop-
lets (
Figure 14.1
)
[1]
.
This self-cleaning behavior, called
superhydro-
phobicity
, is useful for many modern applica-
tions, including stain-resistant paints and roof
tiles as well as coatings for fabrics and other
surfaces that need to stay dry and repel dirt.
Scientists are also studying this effect for lab-on-
a-chip applications, in which hydrophobic and
hydrophilic materials can be used to control the
flow of liquids through microfluidic compo-
nents
[2]
.
Although the self-cleaning properties of lotus
leaves have been documented for millennia and
are being implemented in technological applica-
tions today, there are many other structures,
especially in the animal kingdom, which we
have only recently begin to understand.
Geckos are able to climb on walls or crawl
upside down on ceilings without adhesives.
This remarkable behavior originates on a gecko's
foot. Although smooth in appearance to the
naked eye, this reptile's toes are covered in tiny
structures that allow it to attach to a wide vari-
ety of surfaces (
Figure 14.2
). Indeed, gecko toes
have fine, micrometer-width hairs called
setae
in
the lamellae of their toes. Each seta has about
400-1,000 branches ending in a spatula-like
structure about 0.2-0.5
μ
m long
[3, 4]
.
When a gecko crawls up a surface, these tiny
spatulae “stick” with weak van der Waals forces
to help the gecko's toes temporarily adhere to
nanoscale undulations on a given surface. These
forces are relatively weak compared to normal
FIGURE 14.1
The surface of a lotus leaf has a complex micro- and nanostructured surface to help minimize adhesion, as
shown in (a) the SEM image of a lotus leaf surface and (b) a higher-magnification image with hierarchical structures on the
leaf's surface. A drop of water (c) on the surface of the lotus leaf forms nearly a perfect sphere. Adapted from Ref.
1
, with
permission from SPIE.
