Bioactive Polymers and Nanobiomaterials Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 108

for potential application in orthopaedics and cell-based tissue engineering
applications [101-109]. By incorporating calcium phosphate into CS scaf-
fold both the compressive modulus and yield strength are signifi cantly
improved and a reinforced microstructure has been achieved [106]. The
loading of natural coralline into CS microporous scaffolds was also found
to cause an increase in compressive modulus, and to have a positive
impact on the adhesion of MSCs [107]. The composites of CS/HAp have
been found to promote the formation of bone-like apatite on their surfaces
after soaking in SBF, and to enhance the attachment, proliferation and dif-
ferentiation of osteoblast-like cells [108].
Wan et al. have investigated the interactions of chitin with calcium
species [99]. In one strategy, HAp was dispersed in chitin to produce
intimately blended material. Preliminary mechanical tests revealed a
reduction in strength for the more highly fi lled composites, but they also
revealed retention of the plastic properties of the polymer that may be
favorable for bone substitute applications [99]. Chitin/HAp composites
were also investigated by Ge et al. [103]. HAp in 25%, 50%, and 75% (w/w)
fractions was incorporated into chitin solutions and processed into air-
and freeze-dried methods. These materials were then exposed to cell cul-
tures and implanted into the intramusculature of a rat model, and they
proved to be non-cytotoxic and degradable in vivo . The presence of the
HAp fi ller enhanced calcifi cation as well as accelerated degradation of
the chitin matrix. Composites with various CS/HAp ratios were obtained
by Yamaguchi and coworkers [104] using the co-precipitation method.
In these composites, calcium phosphate formed crystalline HAp when
acetic acid and lactic acid were used in the preparation solvents for CS.
The calcium phosphate was found to be amorphous when organic acids
having more than two carboxyl groups were applied. Biodegradable CS/
Gel/HAp composites were prepared by Zhao [105], and obtained a struc-
ture similar to that of normal human bone as 3D biomimetic scaffolds by
phase separation. By changing the solid content and the compositional
variables, the authors controlled the porosities and densities of the scaf-
folds. Histological and immunohistochemical staining and SEM observa-
tions indicated that the osteoblasts attached to and proliferated on the
scaffolds. The presence of HAp in the CS/Gel composite promoted initial
adhesion of human mesenchymal stem cells (hMSC) and supported long-
term growth in 3D porous CS/Gel/HAp scaffolds [106]. Kong et al. [108]
have investigated CS/nanoHAp scaffolds for bone tissue regeneration,
and studied the bioactivity of the composite scaffolds by examining the
apatite formed on the scaffolds incubated in SBF. The authors suggested
that compared with pure CS, the composite with nanoHAp could form
apatite more readily during the biomimetic process. It is an important
fi nding because cells presented better proliferation on the apatite-coated
scaffolds than on CS scaffolds.