Platinum concentration in silicone breast implant material and capsular tissue by ICP-MS

[Guest guest]

" I would not be terribly surprised if any

physiological reactions to silicone were caused by

unreacted groups left over from the curing reaction,

rather than any properties of the bulk silicone. "

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From: Mark Thorson (nospam@...)

Subject: Re: Platinum concentration in silicone breast

implant material and capsular tissue by ICP-MS

Date: 2004-07-11 21:00:05 PST

I used to work in silicone materials for electronics,

and I know quite a lot about certain aspects of

formulation of silicones. The only metals I am aware

of being used in silicone are:

Platinum, in ppm quantities, for platinum-catalyzed

addition cure systems.

Tin, in organotin complexes, also used as curing

catalysts.

Copper, in organocopper complexes, used to suppress

a ring-scission thermal degradation mode. This would

only be used in silicones intended for

high-temperature applications. I really don't think

there is any possibility these copper additives are

used in medical silicones.

In electronics, the purity of materials is very

important.One of the attractive features of silicone

is that it is easily made in very high purity, with

only trace amounts of metals, far below the level that

could bother anybody.(Far below the levels that occur

in bodily fluids or drinking water.)

I'd be much more concerned about chemically reactive

groups left over from the curing reaction. Silicones

were and are used for implantation in the human body

because they are among the least reactive of plastic

materials.

They are almost totally inert. However, a typical

silicone cure system consists of long-chain polymer

molecules and short-chain crosslinker molecules. Both

the polymers and the crosslinkers have reactive groups

hanging off the ends and the sides. The reactive

groups on the crosslinkers bond to the reactive groups

on the polymers which bridge them together, creating

the polymer matrix, and this is the reaction promoted

by the catalyst. However, sometimes a crosslinker

will bond to a reactive site on a polymer, and it

can't find a reactive site on another nearby polymer

to react with. So even in fully-cured silicone, there

will be unreacted groups left behind, and who knows

what happens to them?

Interestingly, I once had a conversation with one of

the world's top experts on silicone for electronic

packaging on this topic, and there is a way to

eliminate these unreacted groups. You can treat the

cured silicone with ethylene or propylene gas, which

easily permeates into the silicone and reacts with the

unreacted groups. It then easily diffuses out,

leaving no residue. This could be used in electronic

applications, to lower the water absorption of the

silicone (which affects the all-important dielectric

constant) and to improve its stability. As far as I

know, nobody does this. It's an extra-cost process

which almost nobody knows about, even in the silicone

business, so no one even raises the question of

whether it should be done.

I'd be totally amazed if any medical applications of

silicone use this process. And yet, I would not be

terribly surprised if any physiological reactions to

silicone were caused by unreacted groups left over

from the curing reaction, rather than any properties

of the bulk silicone.