X-Message-Number: 3280
Date: 16 Oct 94 23:52:06 EDT
From: Mike Darwin <>
Subject: CRYONICS Silicone Tubing

This is in response to Carlos's somewhat hostile post regarding silastic
materials.  His post doesn't merit a response in terms of decorum, but the
information he gives is incomplete (and somewhat misleading).

It's not quite so simple as Carlos, (or Hugh?), would have it.  Dow is the
primary manufacturer for most of the MATERIAL used to make the other companys'
*silicone* Class VI tubing.  

I am glad to hear Alcor has enough for 16 suspensions (and I would have happily
provided them with the list of the supplier(s) I found to replace the Dow
606-565 tubing we are/were using.


When I called Burlingame Surgical (our usual supplier) to reorder several months
ago, they informed me that Dow had pulled its silastic products in resoponse to
liability concerns and that there was not even a Dow laboratory equivalent
available.  When I talked with others in the marketplace I found the same story
elsewhere: Dow was witholding medical grade silastic material, period (the
reason: the breat implant liability mess).  Several suppliers I spoke with and

several manufacturers told me: "We have no idea what to tell you to do, there is
no product we considerable comparable for replacement of the Dow  601 tubing."

Yes, there are MANY other acceptable Class VI tubings available including
urethanes and PVCs.  But they damage our pump heads during sustained and
frequent long runs at or near zero or subzero xC temperatures; the tubing just
gets too hard and it beats the rollers to death to pump on it (anyone trying to
uncoil a garden hose on a cold or winter day will understand this problem).

I have evaluated laboratory and other manufacturer's Class VI silicone tubing

and I have found several problems: excessive spallation (breaking of microscopic
particles of the rubber into the blood  or perfusate as a result of roller

compression; guess where they end up?), significant variation in wall thickness,
and, a problem which may or may not be related; rupture of the tubing (pump

shoe) during extended pump runs, particularly at high flow during rewarming. Dow
was *the* expert at quality control in this area.

The rupture problem is not likely to be an issue during suspensions since the
flow rates are usually low and the pump run is  either short, or if long, long

at low rpms (flows).  It is, however, a problem for me when we are using a small

diameter pump shoe and asking it to put out 3LPM flow against a substantial back
pressure (narrow bore femoral cannula) during rewarming.  Also, we use a LOT of
the material.  We are doing a dog every week or two.

I should also note that even with the Dow tubing we saw a lot of external spall
(white flakes of tubing) in the pump head after long runs, even with careful
attention to occlusion (adjusting the tightness of the rollers).

We also have special concerns about the tubing surface properties which are not
of a concern in cryonics operations.

In any event, my aside was meant to be helpful to Alcor in alerting them to a
potential problem, not threating or anxiety provoking in any way.  I speak with
Steve Bridge and Hugh frequently, and we both exchange information on problems
of this sort from time to time; Hugh for instance, just recently warned me of a
failure mode he has observed in the liner to our ice water patient air shippers
which might be of concern to me since we both use the same fabricator and
material.

I was well aware that Alcor had a lot of silastic, I bought some of my first
material from them when I started BPI and began doing research.  What I did not
know was how fast they were using it up.  I can only speak to my situation.
When I first made the call I had two experiments scheduled (at considerable

personnel costs with airline tickets purchased, etc) and I had planned to cut my
packs and gas sterilize at the start of the week the experiments were scheduled
for.  Normally, I get silastic tubing *fast* from either of my two suppliers.  

Perhaps I am slower than Hugh on the uptake, but it took me nearly a week to
find what I considered an acceptable possible alternative.  I say possible,
because I have not had the opportunity to try out the new material in-vivo.
Undoubtedly Hugh knows more about tubing than I do, and I hope to profit from

that information at some point.  (Similarly,I have provided Alcor with technical
and procedural information in the past both distant and recent which I think?
they were glad to have.)


If Hugh has some experience with a reliable silastic tubing replacement, I would
really appreciate the information (since Carlos says Hugh doesn't read Cryonet,
I'll copy him on this post).

Another reason for this post was to clarify what I agree should NOT have been a
simple aside in my piece about CSNY/Cryo-Span. I brought it up because it was,
to me, such a *good* example of just how much trouble and inconvenience the
going out of business of a supplier can be to a customer.  I did not know as
much about class VI tubing, or tubing in general as Hugh did when I found I
could not get anymore of a material I knew to be both good and suitable for my
work.  I did NOT appreciate finding myself in the position of getting a crash
education on tubing, and, nearly having to delay experiments (and lose money!).
This was really my point in making the aside in the first place.

Finally, Carlos, in his opening remarks, describes my previous post as an
"apology" for CSNY.  Since Dave Cosenza has so often been accused of merely
expressing Carlos' opinions, I would be curious to know just what Carlos'
opinions vis a vis CSNY/Cryo-Span, Saul and Curtis are?

Mike Darwin

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