Silicones
Silicones are synthetic polymers and are not therefore found naturally. They have a linear, repeating silicon-oxygen backbone akin to silica.
However, organic groups attached directly to the silicon atoms by carbon-silicon bonds prevent formation of the three-dimensional network found in silica.
These types of compound are also known as polyorganosiloxanes. Certain organic groups can be used to link two or more of these silicon-oxygen backbones and the nature and extent of this cross linking enables a wide variety of products to be manufactured.
The most important materials used in medical implants are fluids, gels and rubbers (elastomers) whose physical and chemical properties include, amongst others, a high degree of chemical inertness, thermal stability and resistance to oxidation.
Silicone fluids:
Silicone fluids (oils) are usually linear chains of polydimethylsiloxane (PDMS) which have a wide range of chain lengths and molecular masses.
Cyclic polydimethylsiloxanes also occur and are important intermediates in the manufacture of the linear chain fluids. They are virtually insoluble in water.
Silicone gels:
Silicone gels have lightly cross-linked polysiloxane networks, swollen with PDMS fluid to produce a cohesive mass.
The PDMS fluid is not chemically bound to the cross linked network but is retained only by physical means, as water is in a sponge, and there is a tendency for the fluid to "bleed".
The degree of cross-linking and amount of fluid affects the physical properties of the gel and the rate at which fluid "bleeds" from it. Once suitably cross-linked,
silicone gels retain their form without external containment.
Features of silicone |
