Biomedical Engineering Reference
In-Depth Information
b )
Bioactive:
Bioactive materials are a group of biocompatible materials that
can attach directly with body tissues and form chemical and biological
bonds during early stages of the post implantation period.
c )
Bioresorbable:
Bioresorable materials are the type of biocompatible
materials that are gradually resorbed before they fi nally disappear and
are totally replaced by new tissues
in vivo
.
When a bioinert material is implanted, a capsule-like layer forms on the sur-
face of the implant to keep it isolated from the living part of the body. For exam-
ple, bioinert ceramics, such as alumina or zirconia, develop fi brous capsules at
their interface when implanted. However, it is important to note that the thickness
of an interfacial fi brous layer depends upon motion and the extent of required fi t
at the interface. Therefore, a bioinert material is not useful for long-term applica-
tion. The most signifi cant class of biomaterial is bioactive material, which can po-
tentially behave as the part of a living body. A few examples of bioactive materials
are 45S5 bioglass and calcium phosphates (HA). For bioactive materials, the inter-
facial bond prevents motion between the implant-tissue interfaces and imitates
the type of interface found when natural tissues repair themselves
9
. The third kind
of material is bioresorable or degradable, which degrades with time inside the
body's environment. The degradation rate should be such that the regeneration
rate of new tissue will be same as the material resorption rate. Tricalcium Phos-
phate (TCP) and bone cement are the two examples of bioresorable materials.
1.4 CELL-MATERIAL INTERACTIONS
The interaction between biomaterials and natural tissues is an important scien-
tifi c issue and understanding this issue is essential to designing new biocompati-
ble materials. In understanding the interaction and integration of biomaterials in
a human body, it is worthwhile to mention the physicochemical conditions of the
human body's environment. For example, nominal pH values vary over a wide
range of 1.0 (gastric content) to 7.4 (blood)
10
. Additionally, pH values can change
depending on health conditions (disease, etc.). The temperature of the normal
core of human body is around 37.4 °C; however, deviations over a range of tem-
perature 20-42.5 °C have been reported for diseased patients
10
. As far as the inor-
ganic composition of the human body is concerned, total body burden of Ca, Na,
Cl ions is much higher and also traces of Mg, Fe, Zn, Cu, Al, and so on, are pres-
ent in cytoplasm.
Biologically, a cell is defi ned as a self-duplicating unit, given the proper nutri-
ents and environment. A cell can alternatively be described as a collection of
self-replicating enzymes and structural proteins. In Figure 1.3a, the anatomy of a
typical mammalian eukaryotic cell has been provided. Various important organ-
elles can be identifi ed in Figure 1.3a and important organelles include mitochon-
drion (energy warehouse), Golgi apparatus, Endoplasmic Reticulum (ER), etc. It
can be mentioned here that rough ER is one of the preferred locations for protein
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