Biomedical Engineering Reference
In-Depth Information
the mechanism of
precipitation of biological apatite only; due
to this reason, the mechanical properties of the biocomposites were
not tested [741].
Conventionally, collagen/calcium orthophosphate biocomposites
can be prepared by blending or mixing of collagen and calcium
orthophosphates, as well as by biomimetic methods [33, 36, 38,
41, 594, 597, 609, 686, 703, 708-710, 713, 736, 745-757]. For
example, Tampieri et al. [710] produced and compared artificial
bone like tissue apatite/collagen biocomposites prepared by using
two different methodologies: (1) dispersion of apatite in a collagen
aqueous suspension and then freeze dried and (2) direct nucleation
of an apatitic phase on assembling collagen fibrils. Biocomposites
obtained using first way were similar to uncalcified natural collagen.
The crystallite sizes were not uniform and were often aggregated and
randomly distributed into the matrix, proving that there was no real
interaction between apatite and collagen fibers. However, the second
method allowed the direct nucleation of nano-sized crystals of apatite
on self-assembled collagen fibers. In this case, the two components
(CDHA and collagen) exhibited strong interactions, highlighted by
several analysis techniques, which showed a complete analogy of
the composite with calcified natural tissue [710]. Other production
techniques are also possible. For example, using a polymer-induced
liquid-precursor process, collagen/apatite biocomposites mimicking
the nanostructure of bones, wherein nano-sized crystals of apatite
were embedded within the collagen fibrils, were prepared [757].
More complicated formulations, such as a magnetite enriched HA/
collagen [758] and HA/collagen/PVA [759] biocomposites, have
been developed as well.
Furthermore, collagen might be incorporated into various
calcium orthophosphate cements [713, 738, 760-764]. Typically,
a type I collagen sponge is presoaked in PO
in vivo
4
3−
-containing a highly
basic aqueous solution and then is immersed into a Ca
2+
-containing
solution to allow mineral deposition. Also, collagen I fibers might be
dissolved in acetic acid and then this solution is added to phosphoric
acid, followed by a neutralization synthesis (performed at 25 ºC
and solution pH within 9-10) between an aqueous suspension of
Ca(OH)
/collagen solution [708, 709]. To ensure
the quality of the final product, it is necessary to control the Ca/P
ionic ratio in the reaction solution. One way to do this is to dissolve a
commercial calcium orthophosphate in an acid; another one is to add
and the H
PO
2
3
4
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