General Aspects of Biomimetic Materials - Biotechnologies and Biomimetics for Civil Engineering - page 69

Fig. 3.5 Scanning electron
microscope image of the eye
on a leaf miner moth. Image
source Louisa Howard,
Dartmouth college, Electron
Microscopy Facility, public
domain

100 µ m

Fog-collection. More than 450 million people currently live under water
scarcity in arid regions and two-thirds of the world population are expected to live
in water stressed areas by 2025 as a result of the exponential demographic growth
and the ever increasing rate of water exploitation (Diop and Rekacewicz 2008 ).
Although an inconvenience to drivers, fog is a valuable resource that could be
tapped to alleviate this problem. For example, in arid regions of coastal Africa
(Shanyengana et al. 2002 ) and in the coastline of the Atacama desert in Chile
(Cereceda et al. 2008 ) oceanic fog represents an inexpensive water source, most of
the times more reliable than precipitation or surface water. The integration of fog
collection materials, technologies and structures into buildings, urban environ-
ments and agricultural landscapes could potentially provide fresh water for human
consumption in poor dry countries, provide water to the top of skyscrapers without
pumping, and reduce the exploitation of groundwater for farming purposes. A
wide variety of species, ranging from cactuses to ferns and insects can be found in
arid regions which rely on elaborate fog-collecting strategies that are worth
mimicking in this context. For example, the Namibian desert beetles (from the
genus Stenocara) use a strategy to collect water from the morning fog, which
enables them to survive under the harsh weather conditions characteristic of their
habitat. The water-collecting mechanism used by the Namibian beetle relies on the
bumpy surface of its wings, which combine hydrophilic regions that induce coa-
lescence of water drops, with hydrophobic wax-covered paths that transport water
to the insect's mouth (Parker and Lawrence 2001 ). Several researchers have
directed their efforts towards the development of fog-catching surfaces inspired in
the topography of the wings of Stenocara beetles (Zhai et al. 2006 ; Garrod et al.
2007 ; Dorrer and Rühe 2008 ; Thickett et al. 2011 ). The mechanisms behind the
fog-harvesting ability of cactuses spines (Ju et al. 2012 ; Cao et al. 2014 ) and spider
silk (Zheng et al. 2010 ) have also be studied in detail, constituting excellent
biomimetic models for the development of water collection strategies.