Biomedical Engineering Reference
In-Depth Information
as an osteoinductive material but it becomes osteoconductive in
combination with calcium orthophosphates [699]. Both collagen
type I and HA were found to enhance osteoblast differentiation [700]
but combined together, they were shown to accelerate osteogenesis.
However, this tendency is not so straightforward: the data are
available that implanted HA/collagen biocomposites enhanced
regeneration of calvaria bone defects in young rats but postponed
the regeneration of calvaria bone in aged rats [701]. Finally, addition
of calcium orthophosphates to collagen sheets was found to give a
higher stability and an increased resistance to 3D swelling compared
to the collagen reference [702]. Therefore, a bone analogue based on
these two constituents should possess the remarkable properties.
Furthermore, addition of bone marrow constituents gives osteogenic
and osteoinductive properties to calcium orthophosphate/collagen
biocomposites [1].
The unique characteristics of bones are the spatial orientation
between the nanodimensional crystals of biological apatite and
collagen macromolecules at the nano-scale [39], where the crystals
(about 50 nm length) are aligned parallel to the collagen fibrils [25, 26,
35, 42], which is believed to be the source of the mechanical strength
of bones. The collagen molecules and the crystals of biological
apatite assembled into mineralized fibrils are approximately 6 nm
in diameter and 300 nm long [35, 39, 42, 609, 703]. Although the
complete mechanisms involved in the bone building strategy are
still unclear, the strengthening effect of nanodimensional crystals of
biological apatite in calcified tissues might be explained by the fact
that the collagen matrix is a load transfer medium and thus transfers
the load to the intrinsically rigid inorganic crystals. Furthermore,
the crystals of biological apatite located in between tangled fibrils
cross-link the fibers either through a mechanical interlocking or by
forming calcium ion bridges, thus increasing deformation resistance
of the collagenous fiber network [704].
When calcium orthophosphates are combined with collagen in
a laboratory, the prepared biocomposites appear to be substantially
different from natural bone tissue due to a lack of real interaction
between the two components, i.e
the interactions that are able to
modify the intrinsic characteristics of the singular components
themselves. The main characteristics of the route, by which the
mineralized hard tissues are formed
.
, is that the organic
matrix is laid down first and the inorganic reinforcing phase grows
in vivo
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