Biomedical Engineering Reference
In-Depth Information
Furthermore, shear and tensile forces play a very important role.
Thus, these parameters should also be considered, for example, using
the Mohr circle approach [401]. Besides, it is difficult to compare
the mechanical properties of different cement formulations. For
example, the following numeric values of the compression strength
and setting time were obtained: (i) Norian SRS
®
(~ 50% porosity):
®
33 ± 5 MPa and 8.5 ± 0.5 min, (ii) Cementek
: 8 ± 2 MPa and 17 ±
1 min, (iii) Biocement D
®
(~ 40% porosity): 83 ± 4 MPa and 6.5 ±
®
0.5 min, (iv) α-BSM
(~ 80% porosity): 4 ± 1 MPa and 19 ± 1 min,
respectively [399]. Among them, Biocement D
®
has the highest
compressive strength but the lowest porosity. A high compressive
strength does not necessarily mean that Biocement D
®
is the least
breakable implant [197]. Further details on the major properties
of Norian SRS
®
are available elsewhere [203, 402]. Besides, the
interested readers are suggested to get through the mechanical
characterization of a bone-defect model filled with ceramic cements
[200].
To improve the mechanical properties of the self-setting calcium
orthophosphate formulations, addition of water-soluble polymers
might be considered. For example, in early 1990s, Miyazaki et al.
[403, 404] used a number of polymers, including polyacrylic acid
and polyvinyl alcohol to improve the properties of a TTCP + DCPD
cement. They noted marked increases (up to threefold) in mechanical
properties but with an unacceptable reduction of workability and
setting time. Later, another research group reported similar results
using sodium alginate and sodium polyacrylate [405]. Afterwards,
other researchers added several polyelectrolytes, polyethylene
oxide, and a protein bovine serum albumin into α-BSM
cement
pastes to create calcium orthophosphate—polymer biocomposites
[406]. Biocomposites of α-BSM
®
®
with polycations (polyethylenimine
and polyallylamine hydrochloride) exhibited compressive strengths
up to six times greater than that of pure α-BSM
®
material.
Biocomposites of α-BSM
with bovine serum albumin developed
compressive strengths twice that of the original α-BSM
®
®
cement
[406]. Similar strengthening effect was achieved by addition of
some commercial superplasticizers [407]. The results showed that
small additions, i.e. 0.5 vol. %, in the aqueous liquid phase improved
the maximum compressive strength (35 MPa) of Biocement-H
by
71%, i.e. till ~ 60 MPa. Moreover, the addition of high amounts of
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