Biomedical Engineering Reference
In-Depth Information
1.3.2 Biocompatibility
The fundamental requirement of any biomaterial concerns the ability of the
material to perform effectively with an appropriate host response for the desired
application, that is, the material and the tissue environment of the body should
coexist without having any undesirable or inappropriate effect on each other. This
has also been mentioned in Figure 1.1. Such a requirement is broadly described
by the concept known as ' biocompatibility ' 8 . Broadly, biocompatibility is defi ned
as 'the ability of a material to perform with an appropriate host response in a
specifi c application.' From a biological point of view, biocompatibility arises from
the acceptability of non-living materials (synthetic biomaterial) in a living body
(mammal/human). There are three important aspects of biocompatibility that
a candidate biomaterial seeks to achieve in diverse environments, such as
bone, blood vessel and the eye. In the fi rst place, biomaterials must be biochemi-
cally compatible, non - toxic, non - irritable, non - allergenic and non - carcinogenic;
second, biomechanically compatible with surrounding tissues; and third, a bio-
adhesive contact must be established between the materials and living tissues.
It needs to be emphasized here that the biocompatibility depends on place of
applications. For example, a specifi c material could be biocompatible in bone
replacement, but the same material may not be biocompatible in direct blood
contact application. However, as will be discussed later, a range of in vitro / in vivo
tests are suggested to completely describe the biocompatibility property. It must
be emphasized hence that for a given biomedical application, only a selected set
of relevant tests, among various tests mentioned in section 1.6, should be carried
out on potential implant materials.
1.3.3 Host Response
In order to develop new materials, it is desirable to understand the in vivo host
response of various biomaterials. Ideally, biomaterials should not induce any
change or provoke undesired reaction in the neighboring or distant tissues. An
important aspect of host response involves the formation of a structural and bio-
logical bond between the material and host tissues. When the biocompatibility is
lacking, materials cause tissue reactions, which may be systemic or local. Systemic
responses can be toxic or allergic and triggered by the products of metallic corro-
sion and polymer degradation, release of micro particles from materials, and the
presence of contaminants.
Different human systems (such as respiratory, circulation, or digestive)
respond in different ways to contact with foreign bodies or materials. Depending
on the biocompatibility and host reaction, biomaterials can be broadly classifi ed
into three main categories on the basis of various types of host responses of bio-
materials after implantation into the living body 2 :
a ) Bioinert / biotolerant: Bioinert materials are biocompatible materials,
but cannot induce any interfacial biological bond between implants
and bone.
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