Autoclaving a Device with Dowel Alignment Pins

Have you considered figuring your interferences and assembling at a temperature higher than the autoclave temperature? The ID of the hole will shrink around and capture the pin when it shrinks during cooling after assembly.

Knurling might help, too.

Good Luck.

Thank you yes, I have considered that. My concern is the autoclaving and whether it will be reliable, i.e.holding the pin with the press is fine, but it leaves tiny crevasses to collect bacterior that may not be removed in the autoclaving process. I think a knurl or threads would provide the same crevasses.

You may want to contact some of the adhesive suppliers.

Here's something that might help. I've been away from adhesives too long to make any recomendations.

Good luck!

Choosing Adhesives for Medical Devices - Cover Story - ASSEMBLY

could a 'sweat solder' joint be applied?

I believe you may be sweating this a little too much. There are countless surgical tools that have dowel pins and crevices that are sterilized everyday. As far as the bacteria is concerned, if the sterilizer uses steam for sterilization, and reaches its proper temperature/pressure, for the proper amount of time, the bacteria does not survive. The operator of the sterilizer should run test strips each day to make sure there is no possibility of growth after sterilization. But I would vote for putting it together hot and letting it cool down to fit. IMHO

In autoclaving, the pin fit will be maintained, because both pieces (pin and hole) will expand. The bacteria is killed by autoclaving, but not removed. It seems the existing design should work, unless there is a concern about toxic chemicals being retained in a microscopic crevice.

If every part is of the same material there will be no differential expansion and consequent loosening. We have not had any such problems with medical devices similarly held even on repeated autoclaving.

The pins should not come loose as explained in earlier posts but if you need to be absolutely sure why not use grooved dowel pins to give some extra holding power?

I looked at these. Now I really like that. Very cool. What a neat idea.

One of the major concerns with autoclaving is trapping of condensate in the parts. This issue is often avoided by wrapping the goods to be sterilized (autoclaved) so as to prevent the build up of exess condensate (remember condensate will only be formed when the parts is cold and not when it reaches the sterilization temperature). This part will probably require sterilizing (autoclaving) at >121DegC for at least 15minutes. By the sounds of it air removal will not be an issue, however this would give a more robust sterilization cycle. Also remember that the parts should be dry once the leave the autoclave, the reason being that wet parts are easily recontaminated.

If you have the prototypes ready then I would suggest that you put them through an extended autoclave cycle (say >130degC for 60mins), this will tell you if your concerns are valid or not. Is this a single use or multi use device?

Just one final piece of advice, if the component is required to be sterilized then it should be designed that way. All to often I see devices that have been designed and then they wish for these devices to be sterilized, all to often what you get is a less than satisfactory sterilization cycle.

Is this a reuseable device?

There are a few considerations here.

First issue, can contaminants be introduced into the crevices in its assembled state? If so then prior to all sterilisation these should be removed by an efficient validated decontamination process, whether that is by hot wash, for example reaching 90*c for 1 second or a chemical decontaminant. Only then is a device ready for sterilisation.

Joined parts, when the device is assembled, is hermetically sealed and not subject to contaminant exposure, then it can be sterilised.

As with all objects to be sterilised, they must first be de-contaminated in a validated process.

If de-contamination is achieved only then is sterilisation possible.

Introducing adhesives into a device is only ok if steam, dry heat or gas sterilisation will not alter the composition of the adhesive.

Sterilisation is not about raising the temperature above a threshold but rather it is a process as in the case of steam sterilisation where there are stages to be adhered to in an automatic process. Air removal, Sterilisation plateau of , depending on pressure and temperature, either 134*C for minimum 3.5+ minutes or 121*c for 15 minutes+(for temperature sensitive devices), and then the drying phase. If moisture is still present in a device after sterilisation we cannot accept that as a sterile load as water can be the conduit for bacteria to pass through and is detremental to the integrity of the packaging.

If the bond between the dowel and surrounding material is such that air can pass then steam(if used) will pass also and sterilise. If the two materials are the same then expansion and contraction will be at the same rate and secure.

As with any device that is sold as reuseable then the customer must be offered instructions of the procedures to be followed that will assure them of de-contamination and sterilisation. Also there is an obligation on manufacturers to provide evidence of the device as being capabable of sterilisation.

We usually did rigerous PQ tests on all new devices introduced to proove sterilisation capability.Often we had discussions with manufacturers to make modifications to ensure sterility of a reprocessed device.

All:

It never ceases to amaze me with all the thoughtful answers that appear on this site! Thanks all for your thoughts, I am comfortable with my design now after discussions with the doctor who will be using it, and your comments.

popcornwizard....

Your product desription will not pass the FDA for re-usable, just like Many inferior surgical instruments are classified non-reusable because autovlaving of the joints will not ensure sterility. Your dowels need to have permanent welded unions not floating joints then autoclaving won't be a factor.