Biomedical Engineering Reference
In-Depth Information
metal, 316LVM is Vacuum Arc Remelted (VAR). This process yields
a more uniform chemistry with minimal voids and contaminants. A
reducing atmosphere is preferred for thermal treatment, but inert
gas can be used. 316LVM will fully anneal at 1010
−
1121°C in just a
few minutes. The precipitation of carbides that decreases corrosion
resistance in other 300 series alloys is controlled by reduced carbon
content in 316LVM. This steel has been used for permanent implants
for many years. The corrosion resistance in the annealed condition
is good. This stainless steel has good ductility in the cold worked
condition. Applications include: suture wire, orthopedic cables,
skin closure staples, catheters, stylets, bone pins, and many small
machined parts.
Nowadays, stainless steel is a frequently used biomaterial for
internal ixation devices because of a favorable combination of
mechanical properties, corrosion resistance, and cost effectiveness
when compared to other metallic implant materials (Tables 3.8
and 3.9). The biocompatibility of stainless steel has been proven
by successful human implantation for decades. Metallurgical
requirements are stringent to ensure suficient corrosion resistance,
non-magnetic response and satisfactory mechanical properties [64].
Ta b l e 3
.
8
Typical physical properties for 316L grade stainless steel
Thermal
conductivity
(W/ m
.
K)
at at
100
o
C 500
o
C
Mean coeficient of
thermal expansion
(μm/m/°C)
0-100°C 0-315°C
Speciic
heat
0-100°C
(J/kg
.
K)
Elastic
modulus
(GPa)
Electric
resistivity
(nΩ
.
m)
Density
(kg/m
3
)
8000 193
15.9 16.2
16.3 21,5 500
740
Ta b l e 3
.
9
Mechanical properties of 316L stainless steel
Yield str
.
0
.
2% proof
(MPa) min
Elong
.
(% in 50
mm) min
Hardness
rockwell B
(HR B) max
Hardness
brinell
(HB) max
Tensile str
.
(MPa) min
485
170
40
95
217
In orthopedic and trauma surgery, stainless steel is mainly used
when stiffness is required. The ductility of stainless steel is higher
than that of cp titanium, because of its hexagonal crystal structure.
This makes contouring of stainless steel plates easier, compared to
titanium plates. Therefore, reconstruction plates made of stainless
