Biomedical Engineering Reference
In-Depth Information
generations of bone substitute biomaterials. However, the progress
keeps going and, in current century, scientists search for the third
generation of bioceramics [759], which will be able to “instruct” the
physiological environment toward desired biological responses (i.e.,
bioceramics will be able to regenerate bone tissues by stimulating
specific responses at the molecular level) [41, 43, 56]. One should
note that these three generations should not be interpreted as the
chronological but the conceptual, since each generation represents
an evolution on the requirements and properties of the biomaterials
involved. This means that at present, research and development
is still devoted to biomaterials and bioceramics that, according to
their properties, could be considered to be of the first or the second
generations, because the second generation of bioceramics with
added porosity is one of the initial approaches in developing of the
third generation of bioceramics [781]. Furthermore, there is another
classification of the history of biomaterials introduced by Prof.
James M. Anderson. According to Anderson, within 1950-1975 the
researchers studied bioMATERIALS, within 1975-2000 they studied
BIOMATERIALS and since 2000 the time for BIOmaterials has been
coming [782]. Here, the capital letters emphasis the major direction
of the research efforts in the complex subject of biomaterials. As
bioceramics are biomaterials of the ceramic origin (see section 4.2
General knowledge on biomaterials and bioceramics), the Anderson's
historical classification appears to be applicable to the bioceramics
field as well.
The widespread use of biomaterials, however, experiences
two major difficulties. The first is an incomplete understanding of
the physical and chemical functioning of biomaterials and of the
human response to these materials. Recent advances in material
characterization and computer science, as well as in cell and
molecular biology are expected to play a significant role in studies
of biomaterials. A second difficulty is that many biomaterials do not
perform as desirably as we would like. This is not surprising, since
many materials used in medicine were not designed for medical
purposes. It needs to be mentioned here that biomaterials are
expected to perform in our body's internal environment, which is very
aggressive. For example, solution pH of body fluids in various tissues
varies in the range from 1 to 9. During daily activities, bones are
subjected to a stress of ~4 MPa, whereas the tendons and ligaments
experience peak stresses in the range of 40-80 MPa. The mean load
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