Biomedical Engineering Reference
In-Depth Information
Figure 3
.
2
Implant alloys.
Ta b l e 3
.
5
Mechanical properties of metallic biomaterials [15, 16]
Ultimate tensile
strength [MPa]
Fatigue
strength* [MPa]
Elongation at
fracture [%]
BF
[*10
-3
]
E
[GPa]
Metals
CrNi-steels 490-690
200-250
>40
1-12 210
CoCr-alloys 800-1200
550-650
8-40
1.5-2.3 200
CP-Ti
390-450
150-200
22-30
1.4-1.9 100
Ti-6Al-4V 930-1140
350-650
8-15
3.0-5.6 115
* Rotating bending fatigue.
Unfortunately, these materials have exhibited tendencies to fail
after long-term use due to various reasons such as high modulus
compared to that of bone, low wear and corrosion resistance, and
lack of biocompatibility. The various causes for revision surgery are
depicted in Fig. 3.3 [46].
From the biomechanical point of view, it is desirable to have
a Young's modulus of metallic biomaterials comparable to that
of the cortical bone in order to achieve a good load transfer from
the implant into the bone, leading to a continuous stimulation of
new bone formation (isoelastic material). In order to provide an
E
modulus comparable to that of compact bone (10
−
15 GPa), porous
sintered implants are required. The reduction of Young's modulus
as a function of the porosity can be calculated by means of equation
(3.2) [5]:
