Biomedical Engineering Reference
In-Depth Information
temperature was lowered for the cement with added CF (53 °C compared to
57 °C). Interestingly these research groups found that CF addition increased the
viscosity of the cement above the required level by ASTM standards (ASTM
F451—99a), meaning that use of these cements in a clinical setting would not be
ideal. Fractographic analysis identified poor CF distribution, and evidence of poor
CF-PMMA bonding, although fibre pullout was noted. This CF-reinforced cement
was used in vivo with no detrimental mechanical or biological response observed
after 18 months. During the 1980s, problems associated with the high starting
viscosity of the cement, and subsequent reduced levels of intrusion, were investi-
gated in vitro following the development of low-viscosity cement. Robinson et al.
[
75
] confirmed that CF-reinforcement of a commercial cement increased fracture
toughness of both regular and low-viscosity cements. However, the low-viscosity
cements (both reinforced and conventional) displayed a reduction in fracture
toughness when compared to the equivalent regular viscosity cement. For the
reinforced cement, Wright and Robinson [
98
] reported a decreased crack growth
rate versus the unreinforced cement. Saha and Pal [
77
] investigated the effect of
mechanically or hand-mixed CF-reinforced bone cements, and found that mechan-
ical mixing provided superior performance. They attributed this to the improved
CF dispersion throughout the cement matrix.
8.3.3
Biological Performance
Bone cement is a biologically inert component of the implant construct. However,
conventional acrylic bone cement does not normally promote bone ingrowth. Several
studies however have attempted to improve the biological performance of bone
cement. These have included the incorporation of bioactive agents, such as hydroxy-
apatite-based powders, glass ceramic particles or glass beads [
48,
61,
86
] . Each of
these additives has been reported to enhance the biocompatibility of bone cement,
thus reducing the formation of fibrous tissue at the bone-bone cement interface.
Mousa et al. [
61
] used apatite-wollastonite glass ceramic particles to reduce the
amount of monomer required for polymerisation, which lead to a reduction in the
peak exotherm, and thermally induced bone necrosis, as well as decrease the levels
of cement shrinkage. Similar results have been reported for cements containing
glass beads, which have also been shown to improve bioactivity (in terms of osteo-
conductivity) compared with hydroxyapatite powder [
86
]. Additionally, it has been
reported that many of these bioactive cement composites exhibited no detrimental
influence on mechanical performance, and for some, reinforcements and improve-
ment were observed [
61,
86
]. Concerns regarding biological performance include
the use of antibiotics, which are integrated to reduce the risk of infection and associ-
ated revision [
47
]. Many antibiotic-loaded cements are currently commercially
available and, those containing gentamicin sulphate, are believed not to cause any
adverse affect on the fatigue performance [
6
] .
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