Biomedical Engineering Reference
In-Depth Information
impact direction at an oblique impact angle (15°). However, the wear surface shown in
Figure 6.29b represents that the obviously increased weight loss as well as the high ero-
ero-
sion rate of as-sprayed HACs resulted from a significant brittle fracturing feature by
the normal impact (90°) of the erodent. It is worth noting that the erosion rate of HACs
is significantly decreased at each impact angle after the atmospheric heat treatment. In
addition, the erosion rate is further decreased at each impact angle for the hydrothermally
crystallized coatings, and the HT-HACs show the best wear resistance of all the condi-
high ero-
he condi-
tions. Compared with Figure 6.29b-d, it can be seen that the brittle fracturing feature of
the coating is significantly reduced with the crystallization of the HACs, especially after
the hydrothermal treatment. The HT150 specimen displays a more flattened wear surface
morphology than others, as shown in Figure 6.29d, and it represents that the normal impact
wear resistance is improved after the hydrothermal crystallization. Since the wear frac-
-HACs show the best wear resistance of all the condi-
HACs show the best wear resistance of all the condi-
Since the wear frac-
tures depend on the fracture toughness of a material, the increased fracture toughness can
help to impede crack propagation [99,215] and thus the erosion resistance can be further
enhanced. The reasons can be explained through the measurements of Young's modulus
of the coating layers as described in the previous section. To sum up, the effects of hydro-
he effects of hydro-
thermal crystallization with the self-healing phenomenon on the recovery of mechanical
properties, such as Young's modulus, the bonding strength, and the erosion resistance, in
plasma-sprayed HACs are demonstrated.
as described in the previous section. To sum up, the effects of hydro-
. To sum up, the effects of hydro-
To sum up, the effects of hydro-
StatisticalEvaluationandReliabilityEngineeringforBiomaterials
Unlike mechanical testing methods such as tensile, compressive, shear, and fatigue tests,
under a uniaxial applied force to the experimental specimens, the artificial dental and
orthopedic replacements implanted in human body are always tolerated with a complex
stress field and immersed in the body fluid for a long period. The degradation and failures
may occur from the wear, fatigue, corrosion, and dissolution problems of the implants.
Figure 6.30 illustrates failures at the femur stem and acetabular cup, which resulted from
serious dissolution and dissociation problems of the plasma-sprayed HACs [237]. Failure
types include design deficiencies, quality control, defective materials, mechanical, and
human failures. According to the definition of statistics, failure is recognized as “the event,
or inoperable state, in which any item or part of an item does not, or would not, perform
as previously specified” [238]. If the revision surgery is made for the reestablishment of
implants and artificial joints, the success rate of this revision surgery will be decreased and
the surrounding healthy bone tissues will also be injured during the surgery. Therefore,
in addition to considering the biocompatibility between the implants and surrounding
bone tissues, the evaluation of biological degradation and failures of artificial joints, which
resulted from the dissolution and dissociation for a period of implantation, should also
be made in the fundamental studies and experimental stages. However, the lifetime and
the failure of each product are different and both are influenced by the metallurgical fac-
tors, material design, manufacturing process, and applying systems, even if they are all
produced from the same manufacturing condition and equipment. Thus, the statistical
analysis can help to evaluate the data distribution, statistical significance, and predict the
long-term stability of biomaterials for clinical applications.
In order to prevent early failures and provide a long-term stable implantation for the
plasma-sprayed HA-coated titanium implants or other biomaterials, the reliability
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