Biomedical Engineering Reference
In-Depth Information
freezing or fixation in alcohol render higher quality RNA left in the sample.
Further, for sample handling, as the area of interest is usually close to the
implant surface and requires cutting or sawing and grinding, stabilization
with embedding techniques is required. Different plastic resins which easily
penetrate the tissue are commercially available. these give rise to differences
in volume changes and temperature during curing and the adhesion to the
implant surface varies as well as preserving the antigenicity of the tissue.
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Prior to infiltration and embedding, the tissue undergoes a dehydration where
water is removed with the help of alcohol in a graded series of baths.
15.4 Analysis
A variety of different analytical techniques exist, ranging from static imaging
at different resolution levels to microbiological, chemical, biochemical,
immunological and molecular techniques to identify different components
in the tissue in close proximity to the medical device.
15.4.1 Histology/histomorphometry
qualitative (histology) and quantitative (histomorphometry) morphological
evaluations are mainly based on fixated and resin-embedded ground sections.
The methodology for un-decalcified ground sections of implant and tissue
blocks was first described in the early 1980s and is today the most commonly
used method for histological examination of the tissue response adjacent
to implants in bone. The method consists of tissue fixation, with either
formalin or glutaraldehyde, dehydration with ethanol, resin infiltration and
polymerization. the resin embedded block is then divided along the long
axis of the implant prior to sawing a thin section which is later ground to
a thin section prior to staining.
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important parameters are the sawing
direction and the final thickness of the ground sections.
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subsequent analyses of the stained ground sections are performed in
transmission light microscopy enabling qualitative and quantitative analysis
of the tissue response around the implant. Different polymer resins for
embedding have been used and evaluated such as epoxy, methyl methacrylate
and polyester.
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the polymerization, which most often is performed by
heat treatment, uv-light treatment or by adding an accelerator to the resin,
will result in a hardened block. the hardness will differ between different
polymers and different polymerization methods as well as the degree of
polymerized monomers. An important factor is the viscosity of the resin,
where lower viscosities penetrate the tissue more easily. using an image
analysis software program, different structures may be quantified.
today, in routine studies, most laboratories have developed techniques
for assaying the relative amounts/volumes of tissues adjacent to, inside
