Biomedical Engineering Reference
In-Depth Information
Figure 10.1(a) shows the morphology of the powder of an ABC. Both
PMMA beads and smaller BaSO
4
powder particles are visible.
10.3.2 Processing parameters and setting properties of
acrylic bone cements
At the moment of mixing the solid and liquid components, the polymerization
of the liquid monomer starts, as a typical reaction of addition polymerization
towards curing the paste. The final product, after the polymerization of
the liquid phase, consists of a multiphase material, with the PMMa beads
embedded in a PMMA matrix which also contains the inorganic radiopacifying
fillers. This microstructure can be observed in Fig. 10.1(b), where a SEM
picture of a fracture surface of a cured abC is shown.
Figure 10.2(a) represents schematically the reactants and the product
obtained after the polymerization reaction. both physical and chemical
phenomena take place simultaneously, affecting the setting process as well
as the microstructure and the mechanical properties of the set material, which
depend on variables such as the chemical composition and concentration of
the initial powder and liquid components, the physical mixing method and
chemical environment (Table 10.3).
The time elapsed from the moment in which the powder and liquid
components are mixed until the cement is set is known as the setting time.
If the evolution of the temperature with time is recorded, the setting time
is the time when the temperature of the polymerizing mass is:
T
amb
+ (
T
max
-
T
amb
)/2, where
T
amb
is the ambient temperature, taken as 23 ± 1°C and
600
m
m
(a)
(b)
10.1
(a) Morphology of the powder phase of an acrylic bone cement:
PMMA beads and small barium sulphate white particles are visible,
(b) SEM image of the fracture surface of a cured acrylic bone
cement. PMMA beads are embedded in a PMMA matrix. Scale bar:
600 µm.
