Biomedical Engineering Reference
In-Depth Information
13.2 GLASS DESIGN AND SYNTHESIS
There are two general ways to make a radioactive glass for
in vivo
use.
The first is to add a radioactive substance to the batch materials and to
melt these materials in the normal way so that the radioisotope dissolves
in the melt and becomes an integral part of the glass. This method
has been used successfully, but the special precautions that must be
taken to handle radioactive materials during the melting and subsequent
processing is a serious disadvantage of this method.
The second method is to melt a glass in the normal fashion using
non-radioactive materials and to then make the glass radioactive by
neutron activation as the last step in the fabrication process. This greatly
simplifies the melting and subsequent handling of the glass, because it is
non-radioactive and no special precautions or procedures are required
before the neutron activation step. However, the chemical composition
of the glass is limited in this instance, because many of the elements
commonly present in oxide glass, such as Na, K, and Ca, cannot be
present as they would also become radioactive by neutron activation.
A glass used for the
in situ
irradiation of a target organ and which will
undergo neutron activation should possess the following five general
characteristics [5]. It should be:
(a) biocompatible and non-toxic in the body;
(b) chemically resistant to the body fluids to the extent that none of
the radioisotope is released in the body, and after the radioisotope
has decayed, then release can occur if biodegradability is desired;
(c) made with a composition sufficiently high in a neutron activatable
element so that the level of specific activity needed for the desired
treatment is achieved;
(d) free of any element that will form an unwanted radioisotope during
neutron activation; and
(e) capable of being formed into particles or spheres of the desired size
and shape.
13.3 NON-DEGRADABLE OR BIO-INERT GLASSES:
RARE EARTH ALUMINOSILICATE GLASSES
Many applications require that the glass remains stable in the body and
does not degrade. The composition therefore has to be designed to be
resistant to corrosion in body fluid.
