General Aspects of Biomimetic Materials - Biotechnologies and Biomimetics for Civil Engineering - page 71

The attachment of microorganisms to surfaces also presents a major concern in
public health control. With the recent outbreaks of flu epidemics and the persistent
incidence of hospital-acquired infections, the potential of the inanimate environ-
ment (door and stair handles, hospital surfaces, public transports, etc.) for
spreading diseases has been seriously discussed (Page et al. 2009 ). In hospital
facilities, for example, there is a confluence of multiple pathogenic organisms,
often drug-resistant or contagious strains, which are easily transported in, as well
as out, unless effective anti-microbial measures are taken. Again, the availability
of anti-microbial surfaces could offer architects and engineers a valuable option to
minimize microbial spreading in buildings like hospitals, day-care centers and
food-preparation facilities (Hasan et al. 2013 ; Page et al. 2009 ). A successful
example of a bio-inspired anti-biocolonization surface is described next.
Shark-skin. The search for materials to which organisms struggle to adhere was
primarily motivated by the naval industry. From barnacles, mussels, tubeworms
and algae to microalgae, fungi and bacteria, all sorts of marine organisms get
attached to the hull of ships (Chapman et al. 2013 ). As a consequence, the
hydrodynamic drag increases, fuel consumption soars, the ship's framework cor-
rodes faster and regular maintenance is required to remove the biological layer
(i.e., biofouling) and replenish the cover (Schultz et al. 2011 ). One of the most
interesting developments in the search for new, long-lasting, nontoxic alternatives
to minimize fouling came out from the realization that dermal denticles that cover
the skin of sharks had an unprecedented capacity to prevent microorganisms from
settling. Further studies attributed this capacity to the distinct pattern of tiny
riblets, arranged in diamond shape, on the shark's denticles (Chung et al. 2007 ).
When microorganisms settle on a surface, they signal other individuals of the same
species to induce the formation of biofilms, which help the colonization besides
avoiding detachment. Over the shark skin though, the signalling and biofilm
establishment is inhibited by the topography (Chung et al. 2007 ). This discovery
led to the development of Sharklet TM , ''the only nontoxic, biocide-free and no-kill
surface pattern used to inhibit bacterial attachment, survival and touch transfer-
ence'' (Sharklet 2011 ). In Sharklet TM textured films, the characteristic topography
of shark's dermal denticles was re-interpreted, simplified and optimized, origi-
nating a diamond pattern of ribbons which is easy to produce at large-scale. As a
result, in surfaces covered with Sharklet TM films the settlement of green algae is
reduced by 85 % and bacterial attachment by more than 76 % (Sharklet 2011 ).
The films are currently marketed as being ideal to cover frequently touched bac-
teria-prone surfaces in healthcare buildings or in other facilities where bacterial
absence is desired.
Other natural examples of anti-biocolonization surfaces are the skin of pilot
whale (Globicephala melas), which secretes an enzymatic gel that breaks down the
components of natural glues (Baum et al. 2003 ), the eggs of the white dogwhelk
sea snail (Dicathais orbita), which combine a micro-roughness with oily secretions
(Lim et al. 2007 ) and the wings of cicadas (Psaltoda claripennis), which display a
set of pillars with diameters around 100 nm that mechanically disrupts bacterial
cells (Ivanova et al. 2012 ).