Material Question

A big concern is how much deflection the part will undergo as it is being clipped. If the material is too stiff and/or brittle, you will have problems.

I would also suggest going with the cheapest material you can find. Polyethylene is pretty good, polypropylene (actually a PP copolymer) might be better as that is used in "living hinges" such as you find on one piece boxes (look at cheap tackle boxes for instance).

Properly sterilized, PP is rountinely implanted in the body (sutures, hernia repair meshes, ...) so the nontoxicity issue is fairly minor.

John Aspen Research, -

Opinions expressed herein are my own and may not represent those of my employer.

Polyimide that I know of is not injection molded - it is sintered. Way over engineered for your application. John's recommendation of PE or PP is best. In addition, if this is a medical device, polymer must have device approval. Frank

Frank,

A bit off-topic, but do you mean that the material used for the mold itself must be approved in addition to the material which will make part?

Tim

Good manufacturing process would prevail. If mold release were used, it might need FDA sanction. My limited experience was submitting letter to FDA to allow them to access confidential company file for new medical device approval. I retired from company years ago but they were in process of pulling all their polymer files because of liability problems. Polymer implant would fail and patient would sue everybody, doctors, hospital, device manufacturer and polymer manufacturer. They were winning law suits but spending a fortune to defend for what was for practically no profit from medical aspect of the polymer business.

Without knowing a bit more, it is hard to say what might be the right answer.

It is true that PE, PP and PET are regularly implanted, however, for more structural applications - tuit, those requiring strength like that of human bone - one is stuck with the polyketones (PEEK and PEKK). If you have a halfway developed design, you might try Oxford

It is also true that more than a few polymer companies are getting out of the implantables business, for the reasons stated. There was supposed to be protection for the Med Device supply chain via a law passed in 1998, but the lawyers have figured ways to partially nullify this. Shame, really. Kills innovation.

As before - more detail, please...

rmart> Can someone help me with a suggested plastic material for an injection

It matters little if the material is FDA approved or not, the "FDA approval" is usually only for food contact anyway. Biocompatibility will still need to be proven through testing of the finished device (at least, for medical devices).

Guys,

Thanks so much for your input. Some more info. The device will not be implanted nor should it require FDA approval.

It will clip on the 2 upper frontal teeth. A design challenge in itself. Based on limited research it seems a spring clip type design, with the clip section covering the front of the teeth being relatively flat and the section on the back of the teeth being bowed. See this example of some spring clips (metal)

The contact point of the clip, in the back of the front teeth will be near the base of the tooth and gum, where the tooth is generally recessed and provides somewhat of a grip point. The contact point in the front of the teeth is obvisously flat and needs to contact as much tooth area as possible.

The device will need to withstand some force without falling off. Obvioulsy not a lot, maybe 1-2 lbf.

So I believe what I am concerned about is plastic "tensile strength". We need a good strong grip on a material that is difficult to grip to.

Thanks in advance for your comments.

Randy

rmat> Can someone help me with a suggested plastic material for an injection

I think you will be more interested in the elasticity modulus or flexural modulus. That will give the clamping force. Tensile strength indicates when it will break; and will basically have to be "enough".

Wouter.

From the info that you have given, what is missing is the design. Without a design to use as a starting point, it's hard to speculate on the type of material needed. A material which might fail with a given design might pass with a slight design change. An actual prototype might help in your case. Shaping plastic or metal sheet would be a start. Or, if you have design software to produce files for one of the 3D printing methods; it is relatively easy to get prototypes in a variety of materials. Any prototype would produce valuable information to assist in material selection. Especially when fleshy body parts are involved, real world experiments can help a lot. At least that's the way I see it.

Hey Frank -

Agreed about the FDA th**snip**

I suggest the bottom commenter read CFR21. FDA approves food and drugs and this includes packaging for both and medical devices.

I spent a couple of years in food packaging R&D and we were constantly dancing around the food contact regulations. If someone had a totally new plastic for food packaging, they were told it would cost at least a million dollars and take 5 years to get approval. This was normally a show stopper.

Frank

Yes, but body fluid contact or invitro devices is another thing all together.

As always, it depends (speaking in terms of a device)....