General Aspects of Biomimetic Materials - Biotechnologies and Biomimetics for Civil Engineering - page 66

windows in buildings during flight, most of the times with fatal consequences.
Collision with glass is estimated to cause hundreds of millions of bird casualties
every year in the United States alone, adding up to the man-derived causes for the
decline of bird populations, from hummingbirds to falcons (Sheppard 2011 ).
Conventional strategies to prevent collisions are based on the imprinting of pat-
terns visible to birds on the glass. However, this strategy reduces the passage of
sunlight and may interfere with the building's aesthetics. Searching for a better
solution, the European manufacturer Arnold Glas designed and produced Ornilux, 3
a bird-friendly glass with a UV-reflective cover invisible to human eye. This
solution was inspired by spider signaling through web decorations. In order to
prevent their webs from being damaged by flying birds, spiders include special silk
structures in their pattern that reflect UV light (Bruce et al. 2005 ). This reflex
allows birds to locate and avoid a spider's web without warning their prey. The
coating of glass with a similar pattern of UV reflectors has been claimed to reduce
bird collisions by 76 % (Ornilux 2014 ).
3.3.3 Superhydrophobicity and Self-Cleaning Properties
The external and internal surfaces of buildings are recurrently exposed to liquid,
gaseous, and solid water, whether as a result of rain hitting facades, water vapor
condensing in the ceramic tiles of bathrooms or snow crystals falling down on
roofs. The creation of new materials capable of handling water under these dif-
ferent circumstances in a more efficient way can be foreseen as a way of improving
durability, comfort, and performance of a vast array of surfaces (e.g., tiles, floors,
roofs, walls, etc.) found in buildings. Nature is a source of inspiration in this
regards, since strategies to manage water at surfaces and control wettability are
widely found across organisms due to their relevance in the context of properties
like self-cleaning, drag reduction, adhesion, water capture, condensation and
evaporation kinetics or biofilm formation (Koch and Barthlott 2009 ).
Self-cleaning. In some cases, the accumulation of water layers over the surface
of living organisms is detrimental to vital processes. This is especially critical for
plants, since the deposition of water over their leaves may impede gas exchange,
hinder respiration and interfere with thermoregulation. Moreover, water films and
droplets can partially block the sunlight that is essential for photosynthesis and
allow potentially pathogenic microorganisms to proliferate (Koch and Barthlott
2009 ). Thus, some plants have engineered ways to render their surfaces hydro-
phobic. On hydrophobic surfaces, the energy necessary for liquids to spread is
larger than the cohesive energy between the liquid molecules. As an outcome, the
contact angle, i.e., the angle between the surface and the liquid-air interface, is
high (above 150 for superhydrophobic surfaces) inducing the formation of drops