Civil Engineering Reference
In-Depth Information
reactor, at er 72 h of cultivation, the i nal concentration of the bacterial cellulose was 7.72
g.L
-1
, which was three times higher than that reported for the stirred-tank reactor [53].
h e spherical type bubble column bioreactor (Figure 2.8) is another modii ed air-
lit reactor with spherical shape instead of cylindrical. h rough the addition of small
amounts of agar to the culture medium, low shear stress is achieved as well as high
oxygen transfer rates. As a result, 5.6 g.L
-1
of BC were produced at er 72 hours of culti-
vation [54, 55].
2.2.2
Bacterial Cellulose Properties and Applications
Bacterial cellulose is characterized by specii c and extraordinary properties which allow
applications other than those of plant cellulose. First of all, it is obtained in a highly
pure form, completely free of hemicelluloses, lignin and pectins [4], making it easier to
extract and purify as compared to plant cellulose [7].
BC is characterized by an ultrai ne network structure composed of ribbon-shaped
i brils with an average diameter 100 times thinner than those of plant cellulose i bers
(Figure 2.9) [4]. As a result, BC membranes are a highly porous material with substan-
tial permeability for liquids and gases and high water uptake (water content >90%) [8].
B C n a n o i bers have low density [58] and high degree of polymerization (about 2000-
6000) [4, 59]. In addition, their large aspect ratio and high surface area leads to strong
interactions with surrounding components, resulting, for example, in the retention of
high amounts of water, strong interactions with other polymers and biomaterials, and
i xation of dif erent types of nanoparticles [60], these are fundamental aspects on the
development of novel composite materials as will be discussed latter. BC is also charac-
terized by a high crystallinity index (60-80%) [1, 4, 61, 62], high mechanical strength,
with a tensile strength of 200-300 MPa [1, 4] and a Young's modulus of up to 15 GPa [1,
4, 8, 63]; as well as high thermal stability (with a maximum decomposition temperature
ranging between 340-370˚C) [64].
h e resistance to
in vivo
degradation, due to the absence of cellulases in the human
body, and low solubility of BC may also be advantageous for some tissue engineering
applications [65] .
h e biocompatibility and nontoxicity of BC has also been accessed, through
in vitro
and
in vivo
studies. Several reports indicated that BC is not cytotoxic to chinese hamster
Figure 2.9
SEM images of the surface (let ) (reproduced from [56]) and cross-section (right)
(reproduced with permission from [57]) of a BC membrane.
