Biomedical Engineering Reference
In-Depth Information
was a decrease in the mean diameter of BCP granules and this
influenced the viscosity of the paste. Dissolution of grain boundaries
of β-TCP crystals and precipitation of CDHA on HA crystal surface were
found during the interaction. Both phenomena were responsible for
the observed granulometric changes [900, 901]; however, within the
sensitivity of the employed measurement techniques, no chemical
bonding between BCP and HPMC was detected [1157].
A co-precipitation technique was used to prepare CDHA/chitosan
biocomposites [811]. Growth of CDHA crystals was inhibited by
organic acids with more than two carboxyl groups, which strongly
bind to CDHA surfaces via COO-Ca bonds. Transmission electron
microscopy images revealed that CDHA formed elliptic aggregates
with chemical interactions (probably coordination bond) between
Ca on its surface and amino groups of chitosan; the nano-sized
crystals of CDHA were found to align along the chitosan molecules,
with the amino groups working as the nucleation sites [811].
Formation of calcium cross-linked polymer carboxylate salts was
suggested during setting of calcium orthophosphate cement (TTCP
+ DCPA)/polyphosphazane biocomposites; a chemical involvement
of the polymer in the cement setting was concluded based on the
results of pH monitoring [558-560].
A chemical bond between the phases was presumed in PCL/HA
composites, prepared by the grafting technique [420]; unfortunately,
no strong experimental evidences were provided. In another study,
CDHA/poly(α-hydroxyester) composites were prepared by a low
temperature chemical route [393]. In that study, pre-composite
structures were prepared by combining α-TCP with PLA, PLGA and
copolymers thereof. The final biocomposite was achieved by
in situ
hydrolysis of α-TCP to CDHA performed at 56 ºC either in solvent
cast or pressed pre-composites. That transformation occurred
without any chemical reaction between the polymer and calcium
orthophosphates, as it was determined by FTIR spectroscopy [393].
In nearly every study on HA/carbon nanotubes biocomposites,
the nanotubes were functionalized before combining them with
HA. Most researchers did this by oxidation [303-307], although
non-covalent functionalizing with sodium dodecylsulfate [307] and
coating the nanotubes by a polymer [1158] before combining them
with HA were also reported. Several studies by transmission electron
microscopy revealed evidences that the functionalization enhanced
interaction between carbon nanotubes and HA [306, 307, 1159].
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