Subject: Diffusion/Permeation through PTFE (Gore-Tex)

From: [email-masked]
Date: 28 Jan 1994 16:45:19 GMT

Hi everybody,

	We are using a PTFE membrane covered sparger for aeration of a bioreactor. In
principle this should give bublefree sparging. Now we find that the mass
transfer (klA) is worse than ever. It is actually at 3 orders of magnitude
lower. We are running at 50 ml air/min, a stirrer speed 0f 500 rpm. We checked
all connections and found, that there must be some diffusion limitation. So in
contrast to the claimed increase in klA we have a dramatic loss. Now that
points us to question the diffusion or permeation coeeficient for air, oxygen
and nitrogen thru this membrane (about 1 mm PTFE, porous). And also if there is
a special pressure is required. Any ideas ? Anyone with related experience ?

	I would appreciate any kind of feedback, Thanx!

						Michael R Schuppenhauer
						ETH Zurich, Switzerland
						[email-masked]

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From: [email-masked]
Date: 29 Jan 1994 16:44:28 GMT

In article <[email-masked]>
[email-masked] (Charles N. Haas) writes:
>In article <[email-masked]>, [email-masked]
>wrote:
>
>> 
>> We are using a PTFE membrane covered sparger for aeration of a bioreactor.
>> In principle this should give bublefree sparging. Now we find that the mass
>> transfer (klA) is worse than ever.
>
>The first thing that I would check is the possibility of membrane fouling:
>have you tried this in a sterile, non-fouling system first?
>
>from the keyboard of:         Charles N. Haas:LD Betz Professor of

The system is as of today not anymore non-fouling per se as we incubated the
reactor. Yet, concerning Materials & Methods:

	We received the mebrane, tube of 1 mm thickness on its 316LN ringsparger
(diameter 60 mm) new from Bioengineering Ltd. The sparger was build in, and the
reactor subsequently sterilized. This application is set forth by
Bioengineering as dedicated cell culture bublefree sparging system. However
they are not able to supply data about diffusion etc.
	After sterilization we filled the reactor with sterile Medium for cell culture
(IMDM/F12) and did a sterile test for 80 h. During this time we had bubbling
sparging as we supplied gas directly from the bottle at about 1.3 bara. We
considered everything beeing alright ;( NOT !! So we incubated.
	Then we fixed our massflow controller, sealed everything and went down with
the flow to 50 mln/min. No bubbling. When using nitrogen at 200 ml/min we see
bubbling sparging. The time latencies to reach full saturation with air/oxygen
are so large that measuring a kla is close to impossible. before it was (using
same stirrer assembly & geometry) at about 25 1/h max.
	After realizing our failure we used a new identical sparger to sparge water
and saw the same behavior as stated above. We therefore have no reason to
believe there is fouling going on to inhibit the mass flow, nor is it visible.
The cell concentration is right now still small and DO variations should be so
low that, changes in flow should be easily visible.
	Therefore the question what is different when using this membrane over the
ring sparger to bubble sparging without membrane. To me this points to the
physical characteristics of the PTFE (Gore-Tex) membrane as to say their
diffusion or permeability for gases.

	I hope this additional information helps, and would really appreciate your
help!
							Michael R. Schuppenhauer
							ETH Zurich, Switzerland
							[email-masked]