Civil Engineering Reference
In-Depth Information
and surface area reduced in microbial cellulose composites compared to pristine
microbial cellulose, probably due to the i lling of pores by MMT and chtosan. Water-
holding capacity and water release rate of the composite membrane were found to be
dependent on the nature and arrangement of the composite material on the surface
and inside the matrix of the microbial cellulose sheets [68]. Nge
et al.
[69] fabricated
microbial cellulose/chitosan composite scaf olds having three-dimensional intercon-
necting open-pore microstructure with pore size ranging from 120 to 280 μm through
freeze-drying (−30 and −80°C) and lyophilization of a mixture of microi brillated
microbial cellulose suspension and chitosan solution. h e microi brillated microbial
cellulose was subjected to 2,2,6,6-tetramethylpyperidine-1-oxyl radical (TEMPO)-
mediated oxidation to introduce surface carboxyl groups before mixing. h e integra-
tion of microi brillated microbial cellulose within chitosan matrix was performed by
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC)-mediated
crosslinking. It was observed that freezing temperature and mean pore size have less
ef ect on scaf old mechanical properties, while the compressive modulus and strength
increased with an increase in microi brillated microbial cellulose content. h e observed
improvement in the scaf old rigidity was contributed from closer packing of microbial
cellulose nanoi brils as well as integration of the microbial cellulose nanoi brils web
within chitosan matrix forming the pore walls, which was achieved by EDC-mediated
covalent crosslinking. h e covalent amide bond formed during crosslinking retained
the original shape of the scaf olds during autoclave sterilization.
In 2009, Cai
et al.
[70] prepared a microbial cellulose/chitosan composite by varying
the chitosan concentration and immersion time, and a foam-like structure was obtained.
With increasing chitosan content, the crystalline structure remained unchanged, but
the crystallinity index, tensile strength and Young's modulus of the composites tended
to decrease with increasing chitosan content, but the values were much higher than
for pure chitosan. With the aim of preparing a composite of microbial cellulose and
chitosan for potential biomedical application by post modii cation in an attempt to
use the synergic benei cial aspects of both polymers, Cai
et al.
[71,72] have success-
fully prepared microbial cellulose/chitosan composite by immersing wet microbial
cellulose pellicle in chitosan solution followed by freeze-drying process. h e scaf old
has a very well-interconnected porous network structure and large aspect surface. h e
morphological studies show that chitosan molecules can penetrate into microbial cel-
lulose forming three-dimensional multilayered scaf old. By incorporating chitosan into
microbial cellulose, crystallinity tends to decrease and the thermal stability has a cer-
tain improvement. At the same time, the mechanical properties of composite are main-
tained at certain levels between microbial cellulose and chitosan. It showed much better
biocompatibility than pure microbial cellulose. Since the prepared composite scaf olds
are bioactive and suitable for cell adhesion, these scaf olds can be used for wound dress-
ing or tissue-engineering scaf olds.
Recently, Lin
et al.
[73] successfully produced microbial cellulose and microbial cel-
lulose/chitosan membranes in large scale. h e composite was prepared by immersing
microbial cellulose in chitosan solution followed by freeze-drying. h e incorporation
of chitosan in microbial cellulose (i.e., microbial cellulose/chitosan) led to a more com-
pact i bril network with smaller pore size than microbial cellulose. h e swelling behav-
ior, water retention capacity, moisture content, permeability and mechanical properties
