Page 323 - Advances in Textile Biotechnology

304 Advances in textile biotechnology

Compared with cellulose from plants, bacterial cellulose possesses higher
water holding capacity, higher crystallinity, higher tensile strength, and a

finer web-like network. However, the production cost of bacterial cellulose
is still high compared with that of other natural fibres. Nevertheless, large-

scale microbial cellulose production, through environmentally friendly fer-
mentation processes, appears to be feasible in the future based on the
increased understanding of the biochemical and genetic background of cel-
lulose biosynthesis.

12.6 Future trends

Basic electrospinning can only yield random nanofibres rather than aligned

nanofibres. This can be overcome by using a rotating drum collector (Sub-

ramanian et al., 2005) and the simple or parallel knife-edge disc collector
(Xu et al., 2004), which improves the degree of alignment of the fi bres. The
low productivity of the electrospuns can be solved using multi-nozzle elec-
trospinning devices where several syringes in parallel alignment are used
to introduce the same polymer solution. This is also a method of choice to
obtain blended and even multicomponent nanofibres (e.g. for complex

tissue architectures) when the syringes are loaded with different polymer
solutions. Optimization of the system (by choosing an appropriate solvent

and fibre-forming facilitating product) and process parameters (e.g. electric
potential) in combination with use of a rotating collector and multiple
nozzles is necessary to increase the productivity of aligned continuous fi bres.
Multicomponent nanofibres can be also produced by coaxial electrospin-

ning. In coaxial electrospinning, two concentrically aligned nozzles are used
for spinning and the same voltage is applied to both nozzles. In this instance,
a core–shell nanofibre is created for application in hollow nanofi bres and

nanochannels (Sun et al., 2003). This method is also suitable for fabricating

solid fibres using electrically dissimilar materials. For example, one polymer
may be selected to enhance the mechanical strength, whereas the other
could be chosen to increase the wettability.
The development of an efficient large-scale fermentation technology for

microbial cellulose production at a competitive cost is also required in the
future. For this purpose, a combined use of airlift and stirred-tank reactors,
the use of rotating disk reactors, or continuous cultivation, might be pos-
sible ways to obtain high-productivity bacterial cellulose synthesis at lower
energy cost. Another important approach to raise a good bacterial cellulose
production is the optimization of the culture and the bacterial strain selec-
tion. Improvement in media compositions by selecting appropriate carbon
and nitrogen sources, and incorporating substances that stimulate cellulose
production could also contribute to cost reduction. Escherichia coli and
Salmonella are able to improve the cellulose production with Acetobacter

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