Biomedical Engineering Reference
In-Depth Information
Toxicity
Obviously, biomaterials must not be toxic as they are used inside the human
body. Several tests (see Section 8.7) should be carried out before initiation of a
biomaterial in order to prevent negative effects. Toxicity studies are aimed at
understanding the degree of toxic substances from biomaterial to its environ-
ment. Therefore, chemical and biochemical degradation can be prevented.
8.4
Biomaterials of current cardiac devices
In 1953, the first biomaterial, silicon rubber, was introduced for medical
purposes. Even though it can be used as biomaterial, different types of silicon
rubbers, polydimethyl-siloxane derivatives, were found to be in appropriate for
pump bladders (Poirier, 1997b) because of their weak mechanical properties.
Biocompatible material can be considered in terms of its blood compatibility
(haemocompatible) and tissue compatibility (histocompatible). Haemo-
compatible material should not develop a blood clot (thrombosis), damage
blood cells and activate proteins. Histocompatible material should not be toxic
and allergenic (Lamba et al., 1998). On the other hand, the term `biocompatible'
does not always indicate haemocompatibility of the bulk material.
There are a few criteria which need to be understood about biomaterial. First
of all it is doubtful that one biomaterial can meet all the mechanical and
functional requirements for a blood circuitry device.
Substrate materials may require modification in order to provide the desired
properties for clinical applications. In the early 1990s, researchers tried to
improve the haemocompatibility of bulk materials such as new innovations in
polyurethane material (Szycher and Lee, 1993). For example, although poly-
urethane was a potential polymer as a biocompatible material along with its
excellent mechanical properties, it may not offer the required adequate func-
tional properties for a medical device. In addition, titanium and its alloys were
commonly used for cardiovascular support devices without surface modifica-
tion, yet they have a limitation on haemocompatibility (Sin et al., 2009).
MontiÁs et al. (1997) investigated titanium alloy (Ti
6
Al
4
V) and alumina ceramic
(Al
2
O
3
) for short and middle-term assistance, titanium nitride (TiN), borum
carbide (B
4
C) and diamond-like carbon (DLC) coatings on different kinds of
graphite for long-term and permanent assistance with regard to physiochemistry,
mechanics and tribology. The study shows that a composite material, a substrate
and a coating, is the most appropriate. Aluminium alloy can also be used,
although it is incapable of withstanding corrosion.
In fact, material surface interactions with blood and tissue can lead to serious
complications such as thromboembolism, bleeding and infection. In order to
eliminate these complications, part of the material development research has
shifted to surface modification fields. Therefore, material and its surface
