Biomedical Engineering Reference
In-Depth Information
to each polymer alone [288]. As a rule, with increasing of calcium
orthophosphate content, both Young's modulus and bioactivity of
the biocomposites increase, while the ductility decreases [29, 291].
Furthermore, such formulations can provide a sustained release of
calcium and orthophosphate ions into the milieus, which is important
for mineralized tissue regeneration [287]. Indeed, a combination of
two different materials draws on the advantages of each one to create
a superior biocomposite with respect to the materials on their own.
It is logical to assume that the proper biocomposite of a calcium
orthophosphate (for instance, CDHA) with a bioorganic polymer (for
instance, collagen) would yield the physical, chemical, and mechanical
properties similar to those of human bones. Different ways have
been already realized to bring these two components together
into biocomposites, such as mechanical blending, compounding,
ball milling, dispersion of ceramic fillers into a polymer-solvent
solution, a melt extrusion of a ceramic/polymer powder mixture, co-
precipitation, and electrochemical co-deposition [36, 63, 297-299].
Three methods for preparing a homogeneous blend of HA with PLLA
were compared [297]. A dry process, consisting in mixing ceramic
powder and polymer pellets before a compression-molding step,
was used. The second technique was based on the dispersion of
ceramic fillers into a polymer-solvent solution. The third method
was a melt extrusion of a ceramic/polymer powder mixture. Mixing
dry powders led to a ceramic particle network around the polymer
pellets, whereas the solvent and melt methods also produced a
homogeneous dispersion of HA in the matrix. The main drawback
of the solvent casting method is the risk of potentially toxic organic
solvent residues. The melt extrusion method was shown to be a good
way to prepare homogeneous ceramic/polymer blends [297].
formation, which involves either
synthesizing the reinforcement inside a preformed matrix material
or synthesizing the matrix material around the reinforcement [63,
300, 301]. This is one of the most attractive routes, since it avoids
extensive particle agglomeration. For example, several papers have
reported
Besides, there is
in situ
formation technique to produce various composites
of apatites with carbon nanotubes [302-308]. Other examples
comprise using amino acid-capped gold nano-sized particles as
scaffolds to grow CDHA [309] and preparation of nano-sized HA/
in situ
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