Civil Engineering Reference
In-Depth Information
is similar to the physiological biomineralization of bone-producing apatite crystals
of comparable shape and size. h e CdHAP formed from an octacalcium phosphate
precursor is comprised of anisotropic 10-50 nm crystallites which are elongated in
the c-axis, mimicking the geometry of natural bone apatite crystals, and can make the
i rm intramolecular hydrogen bonding with the microbial cellulose via the cellulose
hydroxyl groups, indicating that microbial cellulose can be used as a template for bio-
mimetic apatite formation. h e formation of a chemical bond between the CdHAP and
the microbial cellulose stabilizes the composite so that it can maintain the mechanical
integrity necessary for bone substitution. When the material is implanted in the body,
chemical bonding would prevent the tiny CdHAP particles from being released to sur-
rounding tissues and initiating dystrophic calcii cation [113]. By having a distribution
of CdHAP bonded throughout the microbial cellulose, the polymer matrix transfers
the stresses to the apatite component in such a way that the particles can bear the load
[114]. It was also reported that CdHAP quickly forms a biomimetic layer of apatite on
its surface, which enables rapid bonding with bone [115]. h e previous studies also
suggest that the presence of CdHAP in this composite will induce bone colonization
when implanted into hard tissue defects [116]. Since CdHAP is the natural mineral
component of bone and CdHAP implants rapidly incorporate into the bone tissue, the
need for a second surgery would be eliminated. h e bioactivity of the CdHAP and
the biocompatibility of the microbial cellulose hydrogel substantiates this composite
as a potential orthopedic biomaterial. Azuma
et al.
[117] concluded that microbial
cellulose-poly(dimethyl acrylamide) double network gel has mechanical properties
similar to the mechanical properties of cartilage and that may meet the requirements
of artii cial cartilage. However,
in-vivo
tests that could coni rm the biocompatibility of
microbial cellulose-based cartilage replacements have not yet been reported. Microbial
cellulose-poly(vinyl alcohol) composites evaluated using unconi ned compression test-
ing also have elastic modulus values similar to those reported for native articular car-
tilage [118] .
Recently, Pretzel
et al.
[119] studied the self-healing capacity of resident cartilage cells
in conjunction with cell-free and biocompatible (but non-resorbable) microbial nano-
cellulose. In the study, standardized bovine cartilage discs with a central defect i lled
with microbial nanocellulose were cultured for up to eight weeks with/without stimula-
tion with transforming growth factor-β1 (TGF-β1). h e study showed that nonstimu-
lated and especially TGF-β1-stimulated cartilage discs displayed a preserved structural
and functional integrity of the chondrocytes and surrounding matrix, remained vital in
long-term culture (eight weeks) without signs of degeneration and showed substantial
synthesis of cartilage-specii c molecules at the protein and mRNA level. Whereas mobi-
lization of chondrocytes from the matrix onto the surface of cartilage and implant was
pivotal for successful seeding of cell-free microbial nanocellulose, chondrocytes did not
immigrate into the central microbial nanocellulose area, possibly due to the relatively
small diameter of its pores (2 to 5 μm). Chondrocytes on the microbial nanocellulose
surface showed signs of successful redif erentiation over time, including increase of
aggrecan/collagen type II mRNA, decrease of collagen type I mRNA and initial deposi-
tion of proteoglycan and collagen type II. h e present bovine cartilage punch model
represents a robust, reproducible and highly-suitable tool for the long-term culture of
cartilage, maintaining matrix integrity and homoeostasis. As an alternative to animal
