Biomedical Engineering Reference
In-Depth Information
only in the latter reaction of apatite cement, larger apatite crystals
were formed due to its addition. Because of larger apatite crystal
formation, the mechanical strength of the α-TCP-added formulation
increased by approximately 30%, as compared to α-TCP-free apatite
cement [454]. Besides, calcium orthophosphate cements might be
reinforced by calcium polyphosphate fibers [458, 459].
To conclude this part, one should briefly mention on the reverse
situation: there are bone concretes made of various polymeric
cements, reinforced by calcium orthophosphate powders or granules
[460-468]. The calcium orthophosphates presented in these
formulations act as fillers, which are necessary to both improve the
mechanical properties and impart bioactivity; they do not participate
in the hardening mechanisms. For example, the higher the amount
of HA was in bioactive acrylic bone cements, the higher were the
compressive and tensile moduli. Furthermore, as the percentage
of HA increased to 20 wt. %, the heterogeneity of the material was
higher [466]. Polymerization of monomers is primarily responsible
for setting of such types of biocomposites and concretes. However,
that is another story.
5.8
Clinical and Medical Applications
Injectable and self-setting calcium orthophosphate formulations
have been introduced as an adjunct to internal fixation for treating
selected fractures. Different studies have already shown that they
are highly biocompatible and osteoconductive materials, which can
stimulate tissue regeneration [22, 469]. The main purpose of calcium
orthophosphate cements, concretes, pastes and putties is to fill voids
in metaphyseal bone, thereby reducing the need for bone graft,
although such formulations might also improve the holding strength
around metal devices in osteoporotic bone. Bone augmentation (i.e.,
a reinforcement of osteoporotic bone through injection) appears
to be a very promising application field of calcium orthophosphate
cements. Such procedures ease the fixation of screws in mechanically
poor bone (for example for osteosynthesis) and decrease pains
associated with unstable vertebrae. The combination of a self-
setting nature, biocompatibility, lack of any by-products and a great
potential for replacement by bones make calcium orthophosphate
cements, concretes, pastes and putties very promising materials
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