Biomedical Engineering Reference
In-Depth Information
within this organic matrix [25, 26, 35, 42]. Although to date, neither
the elegance of the biomineral assembly mechanisms nor the
intricate composite nano-sized architectures have been duplicated
by non-biological methods, the best way to mimic bone is to copy
the way it is formed, namely by nucleation and growth of CDHA
nano-sized crystals from a supersaturated solution both onto and
within the collagen fibrils [705-707]. Such syntheses were denoted
as ''biologically inspired'' which means they reproduce an ordered
pattern and an environment very similar to natural ones [708-710].
The biologically inspired biocomposites of collagen and calcium
orthophosphates (mainly, apatites) for bone substitute have a long
history [33, 442, 597, 711-730] and started from the pioneering
study by Mittelmeier and Nizard [731], who mixed calcium
orthophosphate granules with a collagen web. Such combinations
were found to be bioactive, osteoconductive, osteoinductive [33,
699, 732-734] and, in general, artificial grafts manufactured from
this type of the biocomposites are likely to behave similarly to bones
and be of more use in surgery than those prepared from any other
materials. Indeed, data are available on the superiority of calcium
orthophosphate/collagen biocomposite scaffolds over the artificial
polymeric and calcium orthophosphate bioceramic scaffolds
individually [735].
It has been found that calcium orthophosphates may be
successfully precipitated onto a collagen substrate of whatever form
or source [33, 40, 597, 736, 737]. However, adherence of calcium
orthophosphate crystals to collagen did depend on how much the
collagen had been denatured: the more fibrillar the collagen, the
greater attachment. Clarke et al. first reported the production of a
biocomposite produced by precipitation of DCPD onto a collagen
matrix with the aid of phosphorylated amino acids commonly
associated with fracture sites [716]. Apatite cements (DCPD + TTCP)
have been mixed with a collagen suspension, hydrated, and allowed
to set. CDHA crystals were found to nucleate on the collagen fibril
network, giving a material with the mechanical properties weaker
than those reported for bone. More to the point, the prepared
biocomposites were without the nanostructure similar to that of
bone [713, 738]. The oriented growth of OCP crystals on collagen
was achieved by an experimental device in which Ca
ions
diffused into a collagen disc from the opposite directions [737, 739,
740]. Unfortunately, these experiments were designed to simulate
2+
and PO
4
3−
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