Biomedical Engineering Reference
In-Depth Information
[462]. As to biocomposites of nano-sized HA with PVAP, some indirect
evidences of a chemical bonding among the phases were found by
X-ray diffraction and thermogravimetric analysis [345]. A strong
structural correlation between the orientation of FA crystallites and
gelatin within the FA/gelatin composite spheres was discovered
that indicated to a substantial reorganization of the macromolecular
matrix within the area of a growing aggregate [444]. Recently,
chemical interactions between HA and organic molecules have been
elucidated using
calculation methods [1139].
By means of the X-ray photo-electronic spectroscopy (XPS)
technique, binding energies of Ca, P, and O atoms were found to
have some differences between nano-sized HA (Ca: 350.5 and 345.5;
O: 530.2; P: 132.5 eV) and nano-sized HA/konjac glucomannan/
chitosan biocomposite (Ca: 352.1 and 347.4; O: 531.2; P: 133.4
eV), respectively [653]. Further measurements by FTIR and X-ray
diffraction revealed that nano-sized HA was mainly linked with konjac
glucomannan and chitosan by hydrogen bonding among OH
ab initio
-
and
ions of HA and -C=O and -NH groups of konjac glucomannan
and chitosan copolymer and there was a stable interface formed
among the three phases in the biocomposite. Meanwhile, coordinate
bonding might be formed between Ca
PO
4
3−
2+
and -NH. Stable interfaces
have been formed among the three phases in a biocomposite [653].
In HA/collagen biocomposites, a covalent bond formation between
Ca
2+
−
groups of collagen molecules was found
by XPS [601]. Similar XPS observations were also made for several
other calcium orthophosphate-based biocomposites and hybrid
biomaterials [629, 664, 673].
The interaction and adhesion between calcium orthophosphate
fillers and respective matrixes have a significant effect on the
properties of particulate filled reinforced materials, being essential to
transfer the load among the phases and thus improve the mechanical
performance of the biocomposites [353]. However, for a substantial
amount of the aforementioned formulations, the interaction among
the phases is mechanical in nature. This is because the matrix often
consists of compounds with no functional groups or unsaturated
bonds, which can form ionic complexes with the constituents of
calcium orthophosphates. Obviously, less coupling exists between
non-polar polymers and calcium orthophosphate ceramic particles.
Therefore,
ions of HA and RCOO
polymers
with
functional
groups
pendant
to
the
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