design for medical sterilization question

[njlee]

hi all,

I'm designing a plastic float which will be subjected to medical sterilization such as ETO, autoclaving and hydrogen peroxide gas plasma. I'm thinking about doing a 2-piece design which will be snapped together with o-ring in between for preventing water from getting into the float. I'm trying to get away from adhesives (might not be ok with sterilization process) and ultrasonic welding (too expensive).

Is this kind of design ok for sterilization? I'm worried about the fact that it might not be easy to clean the seam line on the float (where the o-ring is compressed by the 2 parts). I understand that, in general, before sterilization, parts will be thoroughly washed, rinsed and cleaned. I'm not very familiar with the process and the requirements for sterilization. Do I have to design the float so that it can be disassembled for cleaning (worse case for me)?

how do we deal with sealed motor? i think it is the similar case i can think of.

can I say that if the float cannot be disassembled, it needs to be sterilized by gamma ray or e-beam since autoclaving cannot reach area inside the float?

any inputs or thoughts are welcomed. can anyone give me some pointers on where to look for this kind of information (design for sterilization).

Thanks,
lee

 

[MikeHalloran]

Assuming the surrounding pressure is not great, how about using an open bottom float, like an inverted cup? No seams required.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ProbaSci]

Becareful when sterilizing plastic with gamma radiation. It will degrade the material.

Plastic sterilization is a very important topic in orthopedic implants that use plastic bearings to transfer load in artificial joints.

Doesn't plastic float? Can you make it one solid piece?

 

[GenB]

Seamless, yes go seamless, it is the best way, then you can autoclave it, don't you? isn't that what you are trying to accomploish?
ER

 

[njlee]

Thanks for all the replies.

open bottom float is good suggestion.

what i need to know is whether part with seams is an "ok design" (not good design) for medical sterilization. If things get trapped in the seams, pre-sterlization conditioning like rinsing and cleaning is the only way to remove them.

I just realized that the float (2-piece float) might explode if subject to autocalving due to pressure differences.

Thanks,
lee

 

[RichardMc]

On any medical application, be sure that your o-ring materials conform to the USP Class VI standard. This assures a level of biocompatability for the safety of the user.


Richard McInteer

http://www.class-vi-o-rings.com

 

[HEC]

njlee,
What is the function of the float? This may help with recomendations for a solution. As a general guide for sanitary design applications, either completely sealed or fully open and self draining. The inverted bucket is a good idea. Autoclaving is performed with temperature and pressure elevated, therefore crushing of a sealed float may be more a problem than it exploding!



Mark Hutton

 

[Barry1961]

A glass (Pyrex) float should be cheap, stable and no out gassing.

Barry1961

 

[rorschach]

I'd be real concerned about trapped material in the o-ring groove. the o-ring is going to move in the groove with temp and pressure and some pathogens might get trapped under the o-ring and then be exposed again after the sterilization cycle is over. WAY too many med devices are recalled due to sterilization issues. I would not take chances if I could possibly find another way to skin the cat. The only way i could see this working is if the part were either single use disposable, or easily disassembled/reassembled for cleaning. have you considered a solid ldpe or Polypropylene float? it's SG is lower than water (whereas other plastics are slightly heavier) and does not need to be foamed or hollow to float. this strikes me as the easiest way to skin the cat.

 

[Barry1961]

You may be able to put some coating on the float for chemical resistance. Maybe a chrome plating.

Barry1961

 

[unclesyd]

Is metal out of the question?

 

[jmw]

I'm basically a lazy sort so rather than invest time and effort in a new design I would rather talke a moment to review the possible solutions already available, after all, if i have this problem the chances are someone else has already encountered it and solved it. OK, maybe not for this specific application.
My starting point would be a search for float switches and then talk to a couple of manufacturers, you may be able to by the float alone; a ready made float might be fairly easiliy adapted.
For example, if I find a manufacturer of float switches with a stainless steel float I know that this will have been manufactured in mass and will be competitively priced. It will probabley have been spun or or be hydroformed in two parts, machined and EBM welded. The float can then be polished to the appropriate standard for hygienic or Pharmaceutical applications.
The floats used in air release units (Neptune, Liquod Meters etc.) have the added benefit that they are usually foam filled to prevent crushing and as such may not be vulnerable to internal gas expansion (in fact, you might with a suitable float have it EBM welded under vacuum.)


JMW

http://www.ViscoAnalyser.com

 

[Rich2001]

Look at friction welding the parts. This product (a disposible filter)

http://store.ecompressedair.com/detail.aspx?ID=7309

is made from two parts, and friction welded together ( designed for 60 psig).

One half is put in a jig, the top half is placed on and a modified drill press is used to spin the top with respect to the bottom half, welding them together.

Vita sine litteris mors est.