Biomedical Engineering Reference
In-Depth Information
and PLA/HA fibers [233]. These biocomposites are able to consume
a large amount of energy in the fracture.
The action of some coupling agents was found to combine two
distinct mechanisms: (i) cross-linking of the polymeric matrix (valid
for zirconate and titanate coupling agents) and (ii) improvement
of the interfacial interactions among the major phases of the
biocomposites. This interfacial adhesion improvement appeared to
be much dependent on the chemical nature (pH and type of metallic
centre) of the coupling agents [406]. Several works claimed that
silanes do interact with HA [242, 268, 269, 1143-1145]. It was
shown that a silicon-containing inter-phase existed between HA and
PE, which promoted the chemical adhesion between the HA particles
and the polymer. A silane-coupling agent also facilitated penetration
of PE into cavities of individual HA particles, which resulted in
enhanced mechanical interlocking at the matrix-reinforcement
interface [268, 269].
Thus, the optimization of biocomposite properties by coupling
agents is currently an important area of the research. The control
and development of molecular-level associations of polymers with
calcium orthophosphates is suggested to be significant for the
resulting mechanical responses in biocomposites. It appears that
a fundamental molecular understanding of the interfacial behavior
in biocomposites is an area not sufficiently addressed in literature.
Various experimental characterization techniques using electron
microscopy, vibrational spectroscopy, X-ray diffraction, scanning
probe microscopy and others are used routinely to characterize
these materials besides mechanical property characterization. In
addition, atomic scale models for simulating the phase interaction
and predicting responses in the novel material systems, where
nanostructures and nano-interfaces are included, are important to
understand and predict the load deformation behavior [179].
In addition to the aforementioned, the surface of calcium
orthophosphates might be modified as well [144, 509, 510, 656,
1147-1154]. An interesting approach for HA surface modification
was described by Lee et al. [1154]. First,
synthesis of
surface thiol-functionalized HA (HA-SH) was realized by adding
3-mercaptopropionic acid during hydrothermal synthesis of HA,
(Fig. 6.8A). This was followed by grafting polymerization of ethylene
glycol methacrylate phosphate by radical chain transfer generating
in situ
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