Biomedical Engineering Reference
In-Depth Information
mineralization process and bond with HA to form fibroin/HA
nanodimensional biocomposites with increased gelation properties
and, thus, it can be used as an additive to improve cohesion of calcium
orthophosphate cements and decrease a risk of cardiovascular
complications in its application in veterbroplasty and kyphoplasty
[612].
While the simplicity in the processing of cements encourages
the incorporation of cells, the principal difficulty remains to
ensure cell survival. The harsh environment in terms of pH and
high ionic strength together with the high stiffness achieved upon
cement hardening can be thought as the principal threats for cell
endurance. The initial attempts have already been performed but
without a great success yet. For example, researchers have already
found that unset calcium orthophosphate cements might have toxic
effects when placed on cell monolayers, while the set formulations
are biocompatible for the same type of cells (MC3T3-E1 osteoblast-
like cells were tested). A gel encapsulation in alginate beads was
found to be a possible solution to protect living cells for seeding
into self-setting calcium orthophosphate pastes [582, 617].
In vitro
cytotoxic effect of a calcium orthophosphate cement based on α-TCP
was also observed [618]. In light of these results, the encapsulation
approach [308] could potentially be used to seed a patient's
ex vivo
expanded stem cells into a cement to create an osteoinductive bone
graft substitute that could be used to treat that patient. However,
this becomes more related to tissue engineering and biology, rather
than to chemistry and material science. A first possibility would be
designing cement formulations that have setting reactions close
to the physiological pH or by adding additives into the cement
paste able to neutralize the acidic or basic ions released during the
cementation reaction.
Finally, besides the aforementioned chemical, material and
biomedical improvements of the self-setting calcium orthophosphate
formulations, one should not forget on a better design of both
the mixing equipment and delivery (injection) techniques. As an
example, the interested readers are referred to a new cannula to
ease cement injection during vertebroplasty [619]; however, this
subject is beyond the scope of current review.
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