Biomedical Engineering Reference
In-Depth Information
Table 1.3
Room Temperature Tensile Properties of some Bioabsorbable
Magnesium Alloys.
Alloy
Yield Strength
(MPa)
Tensile Strength
(MPa)
Elongation to
Failure (%)
AM60
45
168
19
AM60, ECAPed [317]
240
315
16
AZ61
135
160
7
AZ61, ECAPed [318]
280
315
25
AZ91
150
230
3
AZ91, ECAPed [302]
290
417
8.5
h e most intriguing aspect of recent research on enhancing the proper-
ties of magnesium alloys regards modifying their strength, ductility, and
corrosion behavior to suit them for biomedical applications [270, 272,
319-322]. h e prospect of bioabsorbable magnesium implants has gener-
ated considerable excitement in the medical community, and has been the
subject of comprehensive reviews [274, 323].
h e i rst reported use of pure magnesium in trauma surgery was for a
bone plate in 1907. More recently alloy AZ31 has been used as scaf olds
for cartilage repair, bone screws, plates, pegs, and bands [323, 324]. Part
of the attractiveness of magnesium as a biomaterial is that, unlike other
metals used in orthopedics (titanium, Co-Cr, stainless steel), its corrosion
products have been shown to be physiologically benei cial. For example,
the presence of magnesium aids in mineralization of bone tissue. Several
magnesium alloys have been proposed for medical use including AE21
(2 wt.% Al and 1 wt.% rare earths), AM 60 (6wt.% Al and 0.3wt.% Mn),
WE43 (4 wt.% Y, 3 wt.% rare earths), AZ31 (3 wt.% Al, 1 wt.% Zn), AZ61
(6 wt.% Al, 0.8 wt.% Zn), and AZ91 (9 wt.% Al and 0.7 wt.% Zn). Pure
magnesium corrodes too rapidly in simulated body l uid and in
in vivo
clinical trials. Consequently, the evaluation and development of mag-
nesium for degradable medical implants centers on altering the rate of
corrosion.
h e medical application which has received the most attention is bio-
absorbable vascular stents. Each year over one million stents are placed in
humans to combat atherosclerosis. While the life saving benei ts of these
devices in restoring blood l ow in occluded arteries is unarguable, the rate
of stent failure by in-stent restenosis (ISR) has been as high as 25%. ISR is a
