Biomedical Engineering Reference
In-Depth Information
to the definition of the biological environment in which the biomaterials
need to survive.
in the near future, the challenge of the material scientist will consist
in engineering replacement materials which are able ideally to mimic the
living tissue from a mechanical, but also, from the chemical, biological and
functional point of view. Starting from the example of the best materials
scientist there is, namely nature, the material scientist has to provide the
design of smart structural components that respond,
in situ
, to exterior stimuli
adapting the microstructure and corresponding properties and taking into
account phenomena that occur owing to the specific mechanisms involved
in bone tissue formation such as the biomineralization.
the demand that there is mechanical compatibility with hard tissue
historically led to metals and ceramics being considered more suitable
than polymers for these types of application. However, this approach is not
completely acceptable in many cases, because of mismatches with properties
of natural mineralized tissues. Specifically, metals are preferred for high
strength, ductility and their wear resistance but may offer some problems in
terms of low biocompatibility, corrosion, too high stiffness compared to the
natural tissue, high densities and release of metal ions with possible allergic
tissue reactions.
on the other hand, unreinforced polymers are typically more ductile but not
stiff enough to be used to replace hard tissues in load-bearing applications.
in this context, polymer-based composites are a very convenient solution
for bone repair providing a wider set of options and possibilities in implant
design. Specifically, they may be designed to meet stiffness and strength
requirements for hard tissue substitution.
9.4 Non-degradable composites
Composite biomaterials such as the hip prostheses, fixation plates and screws,
dental post, bone and dental cements represent efforts to find advanced
engineering structures for hard tissue analogues. Carbon and glass fibre
reinforced thermoset polymers (Fig. 9.2) such as epoxy resins were the
first choice for composite orthopaedic prostheses (Ambrosio
et al
., 1987).
Polymer matrices include poly(sulphone) (PS), poly(ether-etherketone)
(PEEK) and poly-etherimide (PEI) (Evans and Gregson, 1998; Alexander,
1996; yildiz
et al
., 1998; akay and aslan, 1995; Shirandami and esat, 1990;
Kettunen
et al
., 1998). These engineering polymers are characterized by high
mechanical properties, thermal stability, very marginal water absorption and
relatively easy processing. in addition, their high level of solvents and thermal
resistance allows the production of sterilizable medical devices. moreover,
the selected materials have demonstrated, at the same time, both positive
and negative properties for specific applications. For instance, PEEK has
