Biomedical Engineering Reference
In-Depth Information
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Al
2
O
3
CoCrMo
SS 316L
Ta
Ti Ti/Ti-6Al-4V
NiTi
b
Ti-alloys
0
10
20
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Porosity (%)
6.12
Variation of Young's modulus as a function of porosity of
alumina and common metallic biomaterials of interest for the
fabrication of scaffolds.
of NiTi foams significantly improves corrosion resistance and decreases
nickel ion release, while barely affecting transformation temperatures.
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Hirschhorn and reynolds
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explored the use of totally porous CoCrMo
implants that had an elastic modulus closer to that of bone, but the porosity
made the strength insufficient for the load. Another approach was to fabricate
porosity-graded composite structures that favour the mechanical anchorage
of cementless joint prostheses.
115, 116
The level of porosity can be graded
from a highly porous to a dense core, giving the component suitable strength
to withstand the physiological loadings while having a porous surface layer
that allows tissue ingrowth.
recently, Lotus-type porous high nitrogen nickel-free stainless steels have
been successfully fabricated using high temperature nitriding.
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The porosity
of the samples oscillated between 44 and 48% and the mean pore size was
in the biomedical field desired range (145-374 mm). When the pores are
aligned perpendicular to the load direction, the mechanical properties are
near to the human cortical bone.
Strongly bonded assemblies of short ferritic fibres constitute an interesting
class of highly porous, permeable materials (Fig. 6.13). It has been recently
proposed that if ferromagnetic fibres are employed, the material can be
actuated by the imposition of a magnetic field.118
118
The resultant deformation of
the fibre array generates a shape change, which can be predicted for a given
