Biomedical Engineering Reference
In-Depth Information
be performed in a sterile environment. Therefore, a mixing procedure
is very important because prior to be injected, a cement paste must
be transferred from a mixing chamber into a syringe. Ideally, this
should be done without trapping air bubbles by the cement paste
[256]. Earlier, most calcium orthophosphate cements were manually
mixed with aqueous solutions using a mortar and either a pestle or a
spatula. That time, some concerns were raised about an insufficient
and inhomogeneous mixing thus compromising the implant
strength, as well as on inconsistencies between operators causing
unpredictable variations in graft performance [257]. Mechanical
mixing (e.g.,
by either an electrically powered mixing machine of
Norian SRS/CRS
®
®
®
or Mini-malax
mixing system for Cementek
cement, produced by Teknimed S.A.) is the modern approach. It
allows mixing the cement paste within 60-80 s and enables a rapid
and reliable filling of the application syringe [34]. Besides, a cement
powder and an aqueous solution might be placed into a syringe and
mixed inside a shaker to produce a consistent cement paste of the
desired viscosity [256]. A mechanical mixing was found to decrease
both the mean viscosity of the curing cement paste and variability in
the viscosity at a given time [258]. However, it did not improve the
mechanical strength of the cement [197, 198].
Of the commercial formulations, listed in Table 5.1, Norian SRS
®
is sold as a reactant pack containing two components: a mixture of
dry powders (MCPM + α-TCP + CaCO
) and a liquid (aqueous solution
3
of Na
). The components are mixed in the operating room. The
paste that is formed is malleable and injectable for ~5 min; it hardens
within ~10 min after injection [22, 206]. However, data are available
that out of 4.5 ml Norian SRS
HPO
2
4
cement paste ~3 ml is injectable
only, whereas up to 1.5 ml of the cement might remain uninjectable
from the syringe [29]. This phenomenon is prescribed to the cement
rheology and its interaction with the hydraulic forces of the syringe.
α-Bone Substitute Material (α-BSM
®
®
) is also a two-component
system; it is prepared from a mixture of ACP and DCPD powders and
a saline solution [169]. Biopex
®
consists of four different calcium
orthophosphates: 75 wt. % α-TCP, 18 wt. % TTCP, 5 wt. % DCPD
and 2 wt. % HA. The aqueous solution contains 12 wt. % sodium
succinate and 5 wt. % sodium chondroitin sulfate [259]. Effects of
liquid phase on the basic properties of Biopex
were investigated.
When mixed with neutral sodium hydrogen orthophosphate or
®
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