Biomedical Engineering Reference
In-Depth Information
Table 2.1 Selected properties of Bioglass [3-6].
Property
Value
2.7 g/cm 3
Density
538 C
Glass transition temperature
677 C
Crystallisation onset temperature
1224 and 1264 C
Melting temperature
10 6 C 1
Thermal expansion coefficient
15.1
×
Refractive index
1.59
Tensile strength
42MPa
Young's modulus (stiffness)
35MPa
Shear modulus
30.7GPa
0.6MPa m 1/2
Fracture toughness
Vickers hardness
5.75GPa
2.1.2 The Materials Properties of Bioglass
Table 2.1 shows various thermal, physical, mechanical and chemical
properties of Bioglass. Bioglass and other bioactive glasses have poor
mechanical properties, with a lower tensile strength and higher modulus
compared to cortical bone (50-150MPa and 7-30GPa, respectively),
which means that they cannot be implanted into load-bearing bone
defects alone. So, they could not be used alone to regenerate a full-
thickness (segmental) bone defect - metallic fixation is required in those
applications to take the cyclic load. Therefore, bioactive glasses and
other bioactive ceramics are more often used to repair defects that are
surrounded by host bone.
However, bioactive glasses can be incorporated in composite struc-
tures and the glass can be formed into scaffolds or fibres to improve
mechanical properties and speed the formation of biomimetic apatite
after implantation.
2.1.3 Mechanism of Bioactivity and Effect of Glass
Composition
The original Bioglass is a quaternary soda-lime-phosphosilicate glass.
The composition is shown in Table 2.2. The silica content is relatively
low compared to window and container glass, to aid dissolution. The
calcium and sodium content is high. This lowers the melting temper-
ature but importantly also aids dissolution. On degradation, owing to
the high content of alkali-metal and alkaline-earth ions, the pH of the
 
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