Civil Engineering Reference
In-Depth Information
composites is signii cantly higher in comparison to the pristine poly(3-hydroxyoctano-
ate) i lm. However, the melting temperature (T
m
) of the composites is lower. An
in-vitro
degradation study carried out in Dulbecco's modii ed eagle medium and in phosphate
buf er saline showed incorporation of modii ed microbial cellulose microcrystal in
poly(3-hydroxyoctanoate) i lm increased the biodegradability of the i lm. And
in-vitro
biocompatibility studies using human microvascular endothelial cells showed a prolif-
eration of 50-110% higher on the poly(3-hydroxyoctanoate)/microbial cellulose com-
posites as compared to pristine P(3HO) i lm.
16.11.3
Cartilage Replacement
Damage on cartilage structures and functions can result from a variety of causes such
as a bad fall or traumatic sports accident, previous knee injuries or wear and tear over
time. Immobilization for long periods can also result in cartilage damage. Articular car-
tilage does not usually regenerate (the process of repair by formation of the same type
of tissue) at er injury or disease leading to loss of tissue and formation of a defect. h is
fact was i rst described by William Hunter in 1743, who stated that, "If we consult the
standard Chirurgical Writers from Hippocrates down to the present Age, we shall i nd,
that an ulcerated Cartilage is universally allowed to be a very troublesome Disease; that
it admits of a Cure with more Dii culty than carious Bone; and that, when destroyed, it
is not recovered" [111]. Due to this limited regenerative capacity of damaged cartilage,
over 1 million patients in the United States require treatment for cartilage defects each
year. Several surgical techniques have been developed in the ef ort to repair articular
cartilage defects. Advanced degeneration of articular cartilage is ot en treated with the
total replacement of joints by prostheses. Due to wear and osteolysis, the lifespan of
these prostheses is limited. Some studies have shown that micronbial cellulose com-
posites could be used as cartilage replacement material. In 2005, Svensson
et al.
[83]
evaluated pristine and chemically modii ed microbial cellulose as a scaf old for tissue
engineering of cartilage using bovine chondrocytes. h e studies showed that unmodi-
i ed microbial cellulose supports chondrocyte proliferation at levels of approximately
50% of the native tissue substrate, collagen type II, while providing signii cant advan-
tages in terms of mechanical properties. However, compared to tissue culture plas-
tic and alginate, unmodii ed microbial cellulose showed signii cantly higher levels of
chondrocyte growth at similar levels of
in-vitro
immune response. Chemical sulfation
and phosphorylation of the microbial cellulose did not enhance chondrocyte growth in
microbial cellulose, while the porosity of the material did af ect chondrocyte viabil-
ity. h e microbial cellulose did not induce signii cant activation of proinl ammatory
cytokine production during
in-vitro
macrophage screening. h e study also coni rmed
that chondrocytes maintain their dif erentiated form when growing on microbial cel-
lulose and that the scaf old supports cell ingrowth. h e Young's modulus of unmodi-
i ed microbial cellulose was in the same range as articular cartilage, while compressive
modulus is lower than articular cartilage.
In 2006, Hutchens
et al.
[112] synthesized a novel composite material consist-
ing of calcium-dei cient hydroxyapatite (CdHAP) and microbial cellulose. In the
study, CdHAP biomimetically deposited in a microbial cellulose hydrogel produced
by Gluconacetobacter hansenii and demonstrated that formation of the composite
