Zhang et al. [138] fabricated CTS/HAp composites by a co-precipitation method
and obtained excellent miscibility with no phase separation between CTS and
nanoHAp in the composite. This could be due to strong specific interactions
between the components, which endows these composites with good mechanical
strength. The maximum compressive strength was about 120 MPa for the
30/70 wt% CTS/nanoHAp composite. In vitro tests showed that degradation of
CTS in this composite takes place and that a layer of bone-like apatite forms on the
surface of the composite, which is a sign of its high bioactivity.
The mechanical resistance of CTS-based composites with HAp was addressed
by Hu et al. [139]. Investigators reported CTS/HAp multilayer nanocomposites
with high strength and bending modulus, rendering the materials suitable for
possible application in internal fixation of long bone fractures.
A wet-chemical method for production of CTS/HAp nanocrystal composites at
low temperature has been demonstrated by Murungan and coworkers [140].
Limitations associated with nanoHAp, such as bioresorption and particle migration,
can be alleviated by this approach. The rate of bioresorption of nanoHAp was
improved by the addition of CTS, and the viscoelastic nature of the composites
prevented the migration of particulate matter into the surrounding tissue upon postimplantation. In addition to these, the smoothness of the composites prevents the
soft tissues around the implant from damage.
Injectable bone substitute material consisting of CTS, citric acid, and glucose
solution as the liquid phase, and tricalcium phosphate powder as the solid phase,
was developed by Liu and coworkers [141]. Four types of cements have been used
to investigate the mechanical properties and in vitro biocompatibility of the material. In the presence of citric acid, tricalcium phosphate partially transformed into
HAp and dicalcium phosphate.
Kong et al. [142] have investigated CTS/nanoHAp scaffolds for bone tissue
regeneration. The bioactivity of the composite scaffolds has was examined by the
incubation of apatite formed on the scaffolds in simulated body fluid (SBF),
followed by study of the activity of preosteoblasts cultured on them. After incubation in SBF, carbonated HAp was formed on both CTS and CTS/nanoHAp
scaffolds. Furthermore, with increasing nanoHAp content in the composite, the
quantity of apatite formed on the scaffolds increased. Here, CTS/nanoHAp
scaffolds formed more than the pure CTS scaffolds during the bimimetic process.
Thus, the cells proliferated better on apatite-coated scaffolds than only on CTS
scaffolds.
CTS/nanoHAp microsphere-based scaffolds were produced by Chesnutt et al.
[143] using a co-precipitation method. The surface area and surface roughness of
composite scaffolds were significantly greater than that of CTS scaffolds. Interestingly, composite scaffolds swelled marginally compared to CTS scaffolds, where
significant swelling was observed, and were thus expected to maintain their shape
intact in vivo. The compressive modulus of composite scaffolds was higher than the
modulus of CTS scaffolds, and both were higher than previous CTS scaffolds
fabricated by other techniques. Osteoblast proliferation was also significantly
increased on composite scaffolds compared to CTS scaffolds. Recently, Kim et al.
[144] obtained a highly flexible HAp/CTS composite film using homogeneously
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
159
and obtained excellent miscibility with no phase separation between CTS and
nanoHAp in the composite. This could be due to strong specific interactions
between the components, which endows these composites with good mechanical
strength. The maximum compressive strength was about 120 MPa for the
30/70 wt% CTS/nanoHAp composite. In vitro tests showed that degradation of
CTS in this composite takes place and that a layer of bone-like apatite forms on the
surface of the composite, which is a sign of its high bioactivity.
The mechanical resistance of CTS-based composites with HAp was addressed
by Hu et al. [139]. Investigators reported CTS/HAp multilayer nanocomposites
with high strength and bending modulus, rendering the materials suitable for
possible application in internal fixation of long bone fractures.
A wet-chemical method for production of CTS/HAp nanocrystal composites at
low temperature has been demonstrated by Murungan and coworkers [140].
Limitations associated with nanoHAp, such as bioresorption and particle migration,
can be alleviated by this approach. The rate of bioresorption of nanoHAp was
improved by the addition of CTS, and the viscoelastic nature of the composites
prevented the migration of particulate matter into the surrounding tissue upon postimplantation. In addition to these, the smoothness of the composites prevents the
soft tissues around the implant from damage.
Injectable bone substitute material consisting of CTS, citric acid, and glucose
solution as the liquid phase, and tricalcium phosphate powder as the solid phase,
was developed by Liu and coworkers [141]. Four types of cements have been used
to investigate the mechanical properties and in vitro biocompatibility of the material. In the presence of citric acid, tricalcium phosphate partially transformed into
HAp and dicalcium phosphate.
Kong et al. [142] have investigated CTS/nanoHAp scaffolds for bone tissue
regeneration. The bioactivity of the composite scaffolds has was examined by the
incubation of apatite formed on the scaffolds in simulated body fluid (SBF),
followed by study of the activity of preosteoblasts cultured on them. After incubation in SBF, carbonated HAp was formed on both CTS and CTS/nanoHAp
scaffolds. Furthermore, with increasing nanoHAp content in the composite, the
quantity of apatite formed on the scaffolds increased. Here, CTS/nanoHAp
scaffolds formed more than the pure CTS scaffolds during the bimimetic process.
Thus, the cells proliferated better on apatite-coated scaffolds than only on CTS
scaffolds.
CTS/nanoHAp microsphere-based scaffolds were produced by Chesnutt et al.
[143] using a co-precipitation method. The surface area and surface roughness of
composite scaffolds were significantly greater than that of CTS scaffolds. Interestingly, composite scaffolds swelled marginally compared to CTS scaffolds, where
significant swelling was observed, and were thus expected to maintain their shape
intact in vivo. The compressive modulus of composite scaffolds was higher than the
modulus of CTS scaffolds, and both were higher than previous CTS scaffolds
fabricated by other techniques. Osteoblast proliferation was also significantly
increased on composite scaffolds compared to CTS scaffolds. Recently, Kim et al.
[144] obtained a highly flexible HAp/CTS composite film using homogeneously
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
159