Biomedical Engineering Reference
In-Depth Information
3.1 Semicrystalline morphology of UHMWPE.
high elongation-at-break, which results in increased resistance against fatigue, a
clinically relevant deformation mode (Bartel et al., 1986). While the ability of
UHMWPE to deform plastically to a large extent leads to high impact and
fatigue resistance, it causes wear under multidirectional shear, another clinically
relevant loading mode. The orientation of the material in the principal direction
of motion weakens the material in the transverse direction (Zhang et al., 2004;
Kurtz et al., 2006) and particle breakup is thought to occur when the material is
loaded in directions other than the principal orientation direction (Jasty et al.,
1997; Fig. 3.2).
Ticona is currently the only producer of medical grade UHMWPE resins
(GUR1020 and GUR1050) used by the orthopedic industry to manufacture
implants. The history of this resin can be traced in the same company back to the
original commercialization of the polymerization of UHMWPE in the 1950s.
The consolidation of the resin is performed at either converter companies or at
the orthopedic manufacturer.
Table 3.1 Physical and chemical properties of consolidated medical grade
UHMWPE
Molecular weight (g/mol)
2±6 million
Density (g/cm
3
)
0.92±0.95
Crystallinity (%)
50±60
Glass transition temperature (ëC)
ÿ160
Melting temperature range (ëC)
100±150
Peak melting temperature (ëC)
133±137
Elastic modulus (GPa)
1±2
Yield strength (MPa)
20
Ultimate tensile strength (MPa)
60
Elongation at break (%)
350±500
