Chemistry Reference
In-Depth Information
scaffold, three levels of porosity can be achieved. The arrangement of fibres
in the yarn determines the accessible space for cells. The inter-fibre space
may be considered as the first level of porosity. This inter-fibre space or first
level of porosity can be controlled by varying the number of fibres in the
yarn and also the yarn packing-density. Further variations in porosity can
be achieved by using twisted, untwisted, textured, untextured, continuous
or spun yarns. At this level, the dimensions are only a few micrometers, and
it is at this level that electrospinning can make the difference in the
production of scaffolds with nano-dimensioned gaps between individual
fibres. The gap or open space between the yarns forms the second level of
porosity.
In the case of knitted scaffolds, the porosity can be varied selectively by
changing the stitch density and stitch pattern, or, in case of woven scaffolds,
by controlling the inter-yarn gaps. Furthermore, a third kind of porosity can
be introduced by subjecting the textile structures to secondary operations
such as crimping, folding, rolling and stacking. In other words, the flexibil-
ity of microstructural parameters is very important for applications such as
scaffold engineering
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. Similar to the microstructural aspects, the mechani-
cal aspects of scaffolds, such as structural stability, stiffness and strength,
have considerable influence on the cellular activity. In tissues like bone, cell
shape is influenced by the cellular activity, and in blood-vessel applications,
the scaffold needs to be strong enough to resist physiologically relevant pul-
satile pressures and, at the same time, match the elasticity values of a native
blood vessel
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.Textile structures are particularly attractive for tissue engi-
neering because of their ability to tailor a broad spectrum of scaffolds with
a wide range of properties.
8.3.7
Heat storage and thermo-regulated textiles
and clothing
Since the dawn of evolution, man has been trying to keep body tempera-
ture at a constant level, around 37 °C, by wearing clothes. Before the devel-
opment of intelligent textiles, body temperature was maintained by adding
or removing layers of clothing. If clothing could automatically change its
thermal resistance according to body temperature, it could provide control
over the rate of heat uptake or release and thereby regulate body tem-
perature. The first thermo-regulated heat-insulating materials appeared in
the late 1980s. The solar-ray selective absorbing textile can absorb the near
infra-red wavelengths of the sunlight spectrum and convert it to heat, thus
enhancing the inner temperature of the clothing. The far-infrared textile can
absorb the body's irradiated far-infrared ray and turn it into heat, enhanc-
ing thermal resistance. Ultra-violet absorbing fabric can absorb the ultra-
violet wavelengths of the light spectrum and reflect the near-infrared rays
