Biomedical Engineering Reference
In-Depth Information
8.3
Reinforcement of Bone Cement
8.3.1
Developments in Acrylic Bone Cement
The intrinsic mechanical properties of acrylic bone cement (such as strength, frac-
ture toughness and fatigue crack propagation resistance) in addition to the presence
of extrinsic factors such as porosity, agglomerates of radiopaque agents and other
such stress concentrations may limit its long-term survival [
52
] . Within the current
literature there have been many attempts to improve the fatigue performance of
bone cement reported. Most studies have tried to control the extrinsic factors, in
particular porosity [
52,
62,
64
], by means of vacuum mixing or centrifugation.
However, this does not address the underlying intrinsic factors which can be broadly
categorised into two areas: (a) mechanical studies, focusing on improving mechani-
cal performance and (b) biological studies where the focus may be on the effect of
bioactive inclusions or the addition of antibiotics.
8.3.2
Mechanical Performance
A significant portion of the literature is directed towards discussing the potential
to increase mechanical performance of acrylic bone cement via reinforcement
with fibres or secondary phase particles: for example, carbon [
70,
72,
75,
77,
98
] ,
polyethylene [
63,
99
] , titanium [
46,
94
] , hydroxyapatite [
81
] , glass beads [
86
] ,
glass fl ake [
26
] , glass fi bres [
63
] and steel [
45
]. Mechanical properties that have
been reported to improve include compressive, tensile and bending strength, elas-
tic modulus, fracture toughness and fatigue resistance, when compared to cement
without reinforcement. In addition to the mechanical improvements provided by
these fillers, further benefits have been identified with reduction in the peak tem-
perature reached during polymerisation. High temperatures experienced in vivo
can cause thermal necrosis of the bone cells surrounding the cement mantle, in
addition to the coagulation of blood, which can potentially lead to aseptic loosen-
ing of the implant, and ultimately implant failure [
50
]. Reduced in situ polymeri-
sation temperatures have been observed for, but not limited to, steel, carbon fibres
and multiwalled carbon nanotube (MWCNT)-reinforced bone cement [
45,
72,
77
]. A number of researchers have investigated adding carbon fibre (CF) as a
reinforcing agent using clinically applicable cement mixing techniques for both
in vitro testing [
70,
75,
77,
98
] and in vivo applications [
72
] . Pilliar et al. [
72
]
reported that the inclusion of randomly oriented CF (0.6 cm) improved fatigue
performance, tensile strength, Young's modulus and impact resistance (i.e. indica-
tive of toughness), compared to cement without reinforcement. The thermal prop-
erties were also observed for the two cement types; the dough time and the setting
time were unaffected by the addition of CF, whilst the maximum polymerisation
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