Testing of anodized aluminum for medical use

A. Hi Glenn. I would not be concerned about byproducts (and cyanide is not used in anodizing).

Two colors, or ten colors, is no problem either.

In view of the rather constant exposure of the public to aluminum, including aluminum foil and cans, and aluminum cooking pots & baking pans, I wouldn't expect allergy issues.

But something that could be a problem is frequent high temperature sterilization because it could certainly cause the dyes to fade. I understand that the Johnson & Johnson Sterrad system can be used on aluminum components. You might talk about this with a specialist in anodizing of aluminum medical components.

A. Normal two-step anodizing will fade with continuous sterilization.

adv.
With the help of Advanced Sterilization Products, a Division of Johnson & Johnson, Highland Plating has developed a process for anodizing aluminum which provides a variety of colors which will withstand the rigors of sterilization. Our system has proven to provide color retention through many processes and is used in a variety of medical applications - including endoscopes, etc.

A. Glenn,

Anodizing in and of itself has no harmful byproducts left over after the process if it's properly done. We anodized oxygen regulators for a company that's now based in St. Louis (they were local to us at one time). They too were concerned about the anodize possibly flaking and peeling and getting into an oxygen stream. In the end it was proven 100% safe and effective.

You might want to have that product patented, I know there are others floating around out there that are considering doing the same thing and they too were going to anodize them. I know this because I did them :-). I wonder if by chance it was for you? You're kind of far away and I do believe this was a local gentleman, but the point being you aren't the only fish in the pond thinking of this and if you'd like your intellectual property protected you should get this product patented ASAP

First of two simultaneous responses --

A. Not that I'm aware of BUT there is a test for proper sealing. ASTM ASTM B136 is the specification to use. Basically a dilute Nitric acid and then a dye to test for absorption. -HTH, Bill.

Second of two simultaneous responses --

A. I've never heard of a bleach test. There is a dye stain test that (for black parts) is often conducted by putting some 1:1 Nitric Acid on the part and checking for color loss, but I've never hear of using bleach for it. Due to the high pH of bleach, I would expect fading (and removal of the anodize layer) if enough time is given regardless of the quality of the finish - anodize doesn't handle high pH all that well.

How did you seal the parts? Were the parts anodized in accordance with a specification (such as MIL-A-8625 / MIL-PRF-8625 [on DLA] )? Do you perform dye stain testing? Do you have some parts still available that you could perform some stain testing on?

A. I love these questions! Relating this back to plating, a lot of people doing electroless nickel refer to EN passing (or not) the nitric acid test. There is no actual ASTM or MIL spec that calls it out yet it is widely used and discussed - many EN data sheets even refer to "passing" the nitric acid test. Bottom line is, it's only relevant to those exposing their EN plated hardware to nitric acid in actual application. Back to the bleach test and its relationship to anodizing - there is this medical instrument industry that continually have their products exposed to bleach for sterilizing. You bet it's important to those instrument manufacturers that are putting a 20-cent black anodize part on their $2,000 instrument. For appearance sakes, there is no fussier a customer than the medical industry but they have a right to be! You should be glad that it's only bleach and not peracetic acid [on eBay or Amazon] sterilization or other even more aggressive chemical / heat combination. Sure we've seen the bleach requirement - it's not to difficult to pass given good dye and suitable seal.