Civil Engineering Reference
In-Depth Information
on the surface of a liquid medium, which had the capability to grow to a thickness of 25
mm and proved to be very strong and tough. Brown also verii ed that this membrane
was generated by a bacterium, initially named
Bacterium xylinum
, but later classii ed as
Acetobacter xylinum
and currently termed
Gluconacetobacter xylinus.
Further research
studies showed that this material had the same chemical composition as the cellulose
produced by plants, and until today bacterial cellulose remains as the most pure exist-
ing natural form of cellulose [5, 6].
Several other species of bacteria of the genera
Gluconacetobacer
,
Sarcina
and
Agrobacterium
have been reported as cellulose producers [4]. However, only
Gluconacetobacter
species can produce cellulose at commercial levels.
Gluconacetobacter
xylinus
remains as a model strain and is used in research and commercial produc-
tion [7]. It is a nonpathogenic, rod-shaped, obligate aerobic Gram-negative bacterium
capable of producing relatively high amounts of cellulose from several carbon and
nitrogen sources [4, 8]. Such bacteria are ubiquitous in Nature, being naturally present
wherever the fermentation of sugars takes place, for example, on damaged fruits and
unpasteurized juices, beers and wines [8]. Recently, we have also reported the pro-
duction of BC by a
Gluconoacetobacter sacchari
strain using dif erent carbon sources
with yields comparable to those obtained with
G. xylinum
[9]. In the latter decades,
the use of BC gained considerable attention in the global scenario of increasing aware-
ness and demand for biobased environmentally-friendly functional materials because
of its inherent abundance, renewability, biodegradability, biocompatibility and specii c
features (particularly the nanometric dimensions and nanostructured network). h e
creation of nanocomposites with diverse partners, as synthetic and natural polymers,
bioactive compounds as well as inorganic NPs constitutes a wide i eld of BC research
and development, as tentatively revised by some authors in the latter years [10-13]. For
instance, Shah
et al.
[11] compiled representative methodologies for BC composites
preparation, some classes of BC composites and their applications, Fu
et al.
[12] sum-
marized the current investigation on BC-based materials for skin tissue repair and Hu
et al.
[13] collected relevant results on functionalized BC derivatives and composites.
However, the domain of BC-based composites is exceptionally vast and in continu-
ous innovation. h erefore, the aim of this chapter is to present a comprehensive, yet
detailed, overview of most relevant results obtained on the production and properties
of BC, and in particular on the design and applications of BC composites with dif erent
partners.
2.2
Bacterial Cellulose Production, Properties and
Applications
2.2.1 Bacterial Cellulose
Production
Bacterial cellulose synthesis by
G. xylinus
starts with the production of individual
β-(1→4) chains between the outer and plasma membranes of the bacterial cell. A single
G. xylinus
cell may polymerize up to 200 000 glucose molecules per second into β-(1→4)
glucan chains, followed by their release outwards through pores in the cell surface [14].
BC chains then assemble into protoi brils, with approximately 2-4 nm of diameter, that
