Biomedical Engineering Reference
In-Depth Information
ideal implant should be adjusted to the healing rate of the human
tissue with absence of any chemical or biological irritation and/or
toxicity caused by substances, which are released due to corrosion
or degradation. Ideally, the combined mechanical strength of the
implant and the ingrowing bone should remain constant throughout
the regenerative process. Furthermore, the substitution implant
material should not disturb significantly the stress environment of
the surrounding living tissue [48]. Finally, there is an opinion, that
in the case of a serious trauma, bone should fracture rather than the
implant [29]. A good sterilizability, storability and processability, as
well as a relatively low cost are also of a great importance to permit
a clinical application. Unfortunately, no artificial biomaterial is yet
available, which embodies all these requirements and unlikely
it will appear in the nearest future. To date, most of the available
biomaterials appear to be either predominantly osteogenic or
osteoinductive or else purely osteoconductive [2].
Careful consideration of the bone type and mechanical properties
are needed to design bone substitutes. Indeed, in high load-
bearing bones such as the femur, the stiffness of the implant needs
to be adequate, not too stiff to result in strain shielding, but rigid
enough to present stability. However, in relatively low load-bearing
applications such as cranial bone repairs, it is more important to
have stability and the correct three-dimensional shapes for aesthetic
reasons. One of the most promising alternatives is to apply materials
with similar composition and nanostructure to that of bone tissue
[40]. Mimicking the structure of calcified tissues and addressing
the limitations of the individual materials, development of organic-
inorganic hybrid biomaterials provides excellent possibilities for
improving the conventional bone implants. In this sense, suitable
biocomposites of tailored physical, biological and mechanical
properties with the predictable degradation behavior can be
prepared combining biologically relevant calcium orthophosphates
with bioresorbable polymers [49, 50]. As a rule, the general behavior
of these bioorganic/calcium orthophosphate biocomposites
is dependent on nature, structure and relative contents of the
constitutive components, although other parameters such as the
preparation conditions also determine the properties of the final
materials. Currently, biocomposites with calcium orthophosphates
incorporated as either a filler or a coating (or both) either into or onto
a biodegradable polymer matrix, in the form of particles or fibers,
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