Posted August 04, 2014
By Tim Cabot
When printing or marking on an anodized aluminum substrate for medical devices, there is much to consider. Before we begin that discussion, a variable to keep in mind is that there are a few printing and marking techniques commonly used:
- Laser etch—creates a permanent mark of varying contrast strength, is environmentally friendly, very clean, and does not require ink.
- Epoxy ink print—commonly used in screen and pad printing, inks harden as they cross-link molecularly and have variable cure times depending on the ink technology deployed (solvent, EV/UV, etc.).
- Sanford Print™—the ink is deposited into open pores of the anodic coating before being sealed, locking in the ink below the surface of the anodic coating; the inks are specialty dye based using soluble dyes, which is not restricted by pore size.
The host of regulations surrounding the manufacturing and use of medical devices requires stringent adherence to established parameters as they relate to safety and efficacy for manufacturers, hospitals, and patients. As well, due to the FDA’s recent implementation of the Unique Device Identification (UDI) system, every medical device will be required to bear a unique, globally recognized identifier so it can be tracked from the point of manufacture, through distribution, to final use. Each of these printing methods has been used on products approved by the FDA.
Anodized aluminum is also widely used in the medical field due to its many sustainable properties. Among its desirable qualities, aluminum is recyclable, lightweight, strong, non-toxic, inexpensive, easily machined, and can be colored. As a reactive metal, it must also be finished to withstand vigorous cleaning and sterilization protocols. There are many variables in play when making basic product design and engineering decisions influenced by the ultimate use of the given medical device or product that impacts what type of printing or marking will work best.
What to Consider—Top 4 Topics
Generally, one should start with the device and the intended application of the device. First tier questions to ask to narrow the choices moving forward are:
1) What Needs to Be Printed?
Okay, so this is obvious, but making the distinction between whether it’s graphics and branding for the supplier or regulatory symbols can make a big difference in how you proceed. Other common prints on medical devices are for device and component identification.
2) Where on the Part Will the Print Reside?
The primary three methods for imparting a print on a medical device are laser, silkscreen, and pad printing. The surface receiving the print dictates which printing method to use. Are your surfaces flat, rounded or irregular, or do they possess tight geometries?
A flat surface can easily receive any of the three methods. The more “difficult” a surface is to print on, the more elaborate and niche the method needs to be to get the desired print. And there may be inherent limitations on where a print can be made on a device. Understanding these variables will help in narrowing your focus.
3) General Characteristics of the Print
The print itself has a strong impact on the methods employed. The image might be solid, a half tone, or a combination of the two. The image may need to be a specific color or multiple colors. As well, the image may need to be unique for serialization purposes or it may be the same image across every part, as in the case of a supplier logo or a regulatory symbol.
Knowing the difference among the methods—laser, conventional silkscreen and pad printing, and Sanford Print™—will be important in determining which one will suit your job the best.
4) How Will the Part Be Cleaned and Sterilized?
Due to the risk of cross infection, all reusable medical devices will need to be frequently cleaned. As most contamination is likely to be organic, cleaning methods typically use chemistries that remove these organic materials. However, depending on the pH of the detergents, an anodic coated aluminum article being cleaned may also be stripped of the anodic coating, at least when the methods use either a very low or very high pH cleaner or when the cleaning cycle is accelerated using heat, higher chemical concentration, or extended cleaning times.
Most cleaning methods use water as the cleaning vehicle, and water is used afterwards to rinse the article and remove any residual chemistry. Therefore, cleaning propagates the conditions that lead to corrosion, especially if the anodic coating is compromised. In the case of laser printing, corrosion can obscure the print to the point of complete loss of the image. (A related subject to review is a new category of micro-crystalline anodic coatings, or MICRALOX®, that have 10x the chemical stability compared to conventional anodic coatings.)
This is just the beginning of the cleaning and sterilization conversation—there’s much more to consider. Be sure to ask all the right questions about what your device is required to undergo in regards to these general topics and protocols to have a clear understanding of your optimal printing and marking options. Click below to read our white paper on "7 Variables you need to consider when Printing and Marking on Aluminum Anodized Substrates on Medical Devices".