Biomedical Engineering Reference
In-Depth Information
incorporation of bioinert ceramics into HA coating was generally adopted. An important
aspect based on the composites concept is the study of the influence of the addition of
other osteogenic materials such as bioinert ceramics on the mechanical performances of
HA coating as well as on bone ingrowth. Bioinert ceramics do not influence the surround-
ing tissue biomechanically, while the bioactive HA has fascinating ability to stimulate a
deposition of calcified tissue to bony tissue if inserted in a bony environment. The bioinert
ceramic is always selected as a secondary strengthening phase in HA coatings owing to
its inherent biological response. Composite materials have a structure comprising two or
more components that differ in physical and chemical properties that have been combined
to provide specific characteristics for particular applications (Yosomiya et al. 1990). Since
a composite coating combines the valuable properties of two or even more components, it
has attracted much attention (Khor et al. 2000; Ramachandran et al. 1998; Gui et al. 2001;
Sordelet et al. 1998). In any structural orthopedic implant, the mechanical behavior of the
composites is a critical contributor to implant performance. As an anisotropic, inhomoge-
neous material, the mechanical behavior of the composite coating is very complex and is
a function of the synergistic properties of the second phase, matrix, second phase/matrix
interfacial bond, and of geometric properties such as particle size distribution and con-
tent in the matrix. Generally, the strengthening mechanism in the composite coating was
believed as (Steinhauser et al. 1997):
• The second phase influences coating structure during coating formation.
• The changes of coating property through the mere existence of the second phase.
The distribution, content, shape, and size of the additives can all affect the eventual per-
formances of composite coatings.
Because of the pronounced brittleness of monolithic HA ceramic, there have been many
efforts toward improving the strength and the toughness of load-bearing biomedical parts
made of HA by adding a second phase. Many ceramic materials have been used in pros-
theses, especially in load-bearing hip prostheses and dental implants owing to the combi-
nation of excellent corrosion resistance, good biocompatibility, high wear resistance, and
reasonable strength. They do not influence the surrounding tissue biomechanically and
they have a significant level of biocompatibility (Gualtieri et al. 1987). Among the materials
used, bioinert ceramics are good at the properties of biocompatibility, biostability, cor-
rosion resistance, compressive strength, impact resistance, fatigue resistance, hardness,
scratch resistance, surface polishing, wettability by fluids, sterilization, and tribology. The
diverse use of bioinert ceramics in clinical application is mainly due to the following valu-
able aspects (Heimke et al. 1987):
• Dense, high-purity ceramic does not influence adjacent tissue biochemically.
• Bioinert ceramic does not stimulate immune reactions.
• No material-induced sarcomas could be detected.
• The remodeling processes of body tissue adjacent to the ceramic implant are the
same as in fracture healing if the same precautions of relative rest along the inter-
face are observed.
• The direct contact of well-proliferating bony tissue can be maintained during
functional loading at all those interfaces along which relative movements can be
excluded. A sufficiently dense arrangement of surface undulations can prevent
relative movements even along tangentially loaded interfaces by interlocking.
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