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Q&As since 1989
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Silver coating endotracheal tubes so deaf babies can be given artificial cochlea
2007
I am trying to help a top surgeon (otolaryngologist) who needs entotracheal tubes (polyuretane) vacuum silver-coated.
At present the wonderful work he does for children is entirely limited by immune response rejection and infection. The use of solid silver tubes has long been shown safe, but we need the flexibility that a vacuum-coated (sputtered or evaporated) silvered tube offers.
In my research days, vacuum deposition of silver onto plastic used to be simple. Now nobody seems willing.
Consultant - Montclair, NJ, US
2007
You may be right, John, but I think the overwhelming majority of this metallized plastic was metallized with aluminum rather than silver.
The plastic tubes could be electroplated if they can't be vacuum metallized. Another approach which might be even better would be to make the tubes by electroforming onto a wax mandrel, then melting away the wax. Of course I haven't seen the part in question.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007
The primary problem is adhesion.
The coating must not rub off under mild finger pressure, for example.
In evaporative vacuum deposition the silver atoms do not strike the plastic with enough energy to adhere, unless some unknown surface prep is given. But in sputtering, silver ions can be energetically propelled by volts to embed in the surface - hopefully just enough to adhere but not to damage the plastic.
The plastic is said to be polyurethane but all the manufacturers refuse to give, or don't know, details. Urethanes are a wide CLASS of differing materials and I do not know which plasticisers are used or anything about carbonyl groups etc on the surface.
MFAssociates - Montclair, New Jersey
Have you thought about some of the coating the tube with some of the new nano silver inks which are available?
These materials are very conductive and cure at reasonably low temperatures (less than 130C)
- Brownstown, Pennsylvania, USA
2007
I am guessing that the Ag is needed because of its anti-bacterial properties. Vacuum metallization would give you very good adhesion. The problem that I see with vacuum metallization is how get the Ag on the inside of the tubes. Vacuum metallization is a line of site process. Unless the ID of the tube is larger than its length I don't see how you can use vacuum metallization to coat the inside of the tubes. A vacuum coater could coat thousand of tubes in a single run. It would require them to build some special fixtures to rotate the parts. Two coating runs may be needed one to coat the inside and the second to coat the outside of the tubes (with proper ID/Length).
From a coaters point the market is small, it is a medical device requiring a lot of extra paperwork and risk, and there is a lot of effort to setup a test run. These maybe the reasons you cannot find a coater.
- Webster, Texas
2007
One possible way to get a thin film to the I.D. of a tube is to use resistive wire such as tungsten, or molybdenum coated with the desired material to be deposited. n electrical current is passed through the wire heating it and evaporating the metal on to the I.D. of the tube.
Of course, the tubing size would dictate the feasability of the job.
- Lompoc, California, USA
2007
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