Chemistry Reference
In-Depth Information
Applications
10.1 MEDICAL
Numerous medical applications have been developed for siloxane poly-
mers.
1-4
Prostheses, artificial organs, objects for facial reconstruction, vit-
reous substitutes in the eyes, tubing and catheters, for example, take
advantage of the inertness, stability, and pliability of polysiloxanes. Arti-
ficial skin, contact lenses, and drug delivery systems utilize their high per-
meability as well. Such biomedical applications have led to extensive
biocompatability studies,
5-6
particularly on the interactions of polysilox-
anes with proteins.
7
There has been considerable interest in modifying
these materials to improve their suitability for biomedical applications in
general.
8-9
Advances seem to be coming particularly rapidly in the area of
high-tech drug-delivery systems.
10 -11
Figure 10.1 shows the range of diam-
eters of Silastic medical-grade siloxane tubing available for medical ap-
plications. The smallest tubing has an internal diameter of only 0.012
inches (0.031 cm) and an outer diameter of only 0.025 inches (0.064 cm).
Such materials must first be extensively tested (sensitization of skin,
tissue cell culture compatibility, implant compatibility). There has been
considerable controversy, for example, over the safety of using polysilox-
anes in breast implants.
12-13
The major concern was “bleeding” of low mo-
lecular polysiloxanes out of the gels into the chest cavity, followed by
transport to other parts of the body. The extent to which “bleeding” oc-
curred and its possible systemic effects on the body were argued vigor-
ously in the media and in the courts, and led to restrictions on the use of
polysiloxanes.
In the case of controlled drug-delivery systems, the goal is to have the drug
released at a relatively constant rate (zero-order kinetics) at a concentration
