Carbon Nanotubes in Acrylic Bone Cement - Biologically Responsive Biomaterials for Tissue Engineering - page 177

the polymerisation process that numerous cement properties, for example viscosity,
setting time, maximum cure temperature, volumetric shrinkage, etc., can be deter-
mined. These material characteristics may influence the performance of a cemented
TJR. It has also been shown that the variability in the mechanical static and dynamic
properties of commercial bone cements is significant, with greater relative differ-
ences reported in fatigue properties [ 33, 50 ] . Harper and Bon fi eld [ 33 ] found that
there was some correlation between the static and fatigue strengths; however the
ranking of the different cements tested did not match exactly. Mechanical properties
are known to be affected by cement composition, size and morphology of the
PMMA beads, molecular weight, cement mixing technique and powder-liquid ratio
[ 33, 50 ]. The variation in tensile strength, for example, is reported to vary between
24 and 49 MPa for five different commercial bone cement formulations, depending
on the mixing technique, specimen age and test conditions [ 50 ] .

8.2.5 Biocompatibility of Bone Cement “In Vivo”

Any biomaterial must exhibit some level of biocompatibility. An orthopaedic
implant has the potential to alter both the mechanical and chemical environment
locally (within the immediate surroundings) and systemically (throughout the whole
body) [ 73 ]. The implantation of any material into the human body poses the risk of
an immune response, involving inflammation of the local region, and potential
rejection of the implanted material [ 34 ]. Traditionally PMMA has been accepted as
a biocompatible or a bioinert material [ 5 ]. The potential for an immune response
associated with the use of bone cement stems from the presence of unreacted resid-
ual MMA monomer; however, this MMA is rapidly removed from the body via the
lungs, minimising systemic and cardiovascular reactions [ 19 ] . Osteolysis refers to
an active resorption of bone due to disease, infection or inadequate blood supply
[ 57 ]. Osteolysis is often associated with aseptic loosening, which has been shown to
be the most common cause for revision surgery [ 43, 44, 82 ]. It has been reported
that bone cement can lead to the onset of peri-prosthetic osteolysis (i.e. bone resorp-
tion around the implanted construct) in the form of small fragments [ 19, 32 ] . These
small fragments may be generated as wear particles between articulating surfaces
and, in excess, these particles are deposited in the surrounding tissue causing an
inflammatory response. Additionally, wear particles may be generated during
fatigue crack propagation of the cement mantle, and migration of these particles
into the surrounding tissue is then possible [ 94 ] .

8.2.6 Effect of Residual Stresses and Cement Shrinkage

It is well accepted that residual stresses are generated within the cement mantle fol-
lowing polymerisation and have a direct influence on the stress distribution at the
cement-prosthesis interface. Knowledge and understanding of these processes may