Aluminum is the material of choice for a variety of non-invasive parts, such as handles and grips, electronic houses, couplings, knobs, and levers, etc. used in the design of complex surgical instruments. These medical devices—which require both a protective/decorative coating of the aluminum substrate, as well as printing on the device—undergo repeated cleaning and must withstand a variety of increasingly harsh conditions and processes required to eliminate the risk of contamination and cross infection.
Anodic coatings employed in aggressive environments requiring regular cleaning, sterilization, or exposure to harsh, corrosive environments must sustain vigorous performance thresholds. These coatings cannot be achieved by certifying to Mil 8625 standards or other commodity specifications, or through minor modifications to long-practiced metal finishing processes.
To produce specialty anodic coatings that withstand such conditions, it takes new technology, a systematic development approach, clear performance testing protocols, and investment in novel process technologies. Precision Coating and our sister company, Sanford Process Corporation, have been at the leading edge of anodic coating developments for over 40 years and, launched microcrystalline anodic coatings in 2012, along with a series of breakthrough embedded printing techniques geared to deliver exceptional performance in aggressive environments.
Our goal is to allow our customers to achieve record-breaking and consistent and predictable functional performance for customer products while also satisfying their design requirements. Like all Sanford Process low-voltage hard coat technologies, microcrystalline anodic coatings can be left clear and transparent with minimal darkening or colored in a wide range of vibrant colors.
To fully appreciate the importance of phase changing an amorphous oxide to partially crystalline oxide that is at the root of MICRALOX performance, it’s important to understand what lead to the development of this new technology. Read about the many elements of the journey that lead us to create MICRALOX. You can follow along chronologically or jump to sections that interest you most.
- Anodizing Aluminum for Medical Applications: The Creation of MICRALOX® and the Failings that Lead to It
- A Brief History
- Chemistry and Cleaning
- Exploring Alternatives to Aluminum Anodizing for Reusable Medical Devices
- Investigating the Problem
- Finding the Monster
- The Two-Fold Truth about the Failing
- Micro Crystalline Aluminum Oxide
- Creating MICRALOX
- Sister Chemistries
- 50 Times Longer Protection
- Marking and Graphics
- Transformational Advances
Anodizing Aluminum for Medical Applications: The Creation of MICRALOX® and the Failings that Lead to It
Demand for high performing, reusable aluminum anodized medical products has never been higher. However, driven by poor performing anodic coatings where conventional amorphous anodic coatings dissolve progressively over each cleaning cycle resulting in coating failure, the medical industry first attempted to replace aluminum anodized products with several substitutes. The substitute materials chosen to replace anodized aluminum, whether plastic or less corrosive metals, have all had their share of problems as well.
Without better choices, there has been a certain amount of end-user tolerance for these poorer performing anodized medical devices, because it was accepted that this was inevitable to the conditions that the medical industry exposed them to; and effort was focused on trying to reduce the most egregious harm by restricting detergents to neutral-pH cleaners.
There are two problems in particular:
- Fading of color during sterilization
- Dissolution of the coating during cleaning with more aggressive cleaning agents, either due to pH, detergent concentration, or cleaning temperature
Moreover, there has been an increased call to guarantee sterility and to eliminate the causes of cross infection. Cleaning studies undertaken to demonstrate that the articles can be cleaned and sterilized resulted in greater awareness about the poor performance of conventional aluminum anodizing. This coincided with a market trend towards aluminum components, as such components command a premium position due to superior look and feel. Since all the substitution choices had their own negative issues, the medical world has turned to the anodizing industry to improve anodic coating technology.
MICRALOX® was born of this demand, which is increasing the chances that anodized aluminum medical devices will remain the top choice of manufacturers.
Anodizing on aluminum has been a widely accepted and significantly utilized metal finishing option for reusable, non-invasive medical products within the medical component manufacturing community for many years. The history of using anodizing as a medical finish dates back to when the first aluminum medical product was manufactured some 60-plus years ago. The benefits of this finish have been thoroughly examined, tested, and re-tested since that first aluminum product was introduced. Its durability, multiple and varied cosmetic choices due to its dye-ability, along with the low-cost advantage that aluminum anodizing carries, have long been the driving forces behind its world-wide acceptance as an aluminum finishing choice. The medical industry latched on to the anodizing band wagon as it began to soar in popularity in the 1960s and 70s—and for good reason.
Anodized aluminum created significant advancement in the areas of reusable medical instruments, components, and more recently, sterilization trays, as well as many other areas. Its use allowed and presented tremendous flexibility with product design due to the relative ease of machining and forming of aluminum. In addition, the light-weight nature of aluminum was, and continues to be, an important consideration given the alternatives. The fact that aluminum can be anodized for protection, wear resistance, and cosmetics, gave it the lead in the race for the best medical instrument material choice. And unlike plastics, aluminum anodized articles dry quickly, eliminating the need for drying steps after washer disinfecting or autoclave sterilization.
In the last several years, however, this is being re-examined. The medical case and tray industry, along with the medical device industry, has begun to place higher performance demands on reusable aluminum anodized products. This demand is being primarily driven by the medical care-giver’s need to clean, sterilize, and disinfect with more aggressive chemistries. The increased performance requirement of anodizing became necessary after it was discovered that cleaning in high-pH chemistry could be used in an effort to eliminate prion disease-causing proteins, and this method of cleaning has now found general acceptance in the European medical arena. As the chemical treatments that have proved effective in this cause became harsher and more aggressive, anodized aluminum finally began to show its weakness. Up to this point, anodized aluminum was enjoying an unmatched popularity as a material and finishing of choice.
As an amorphous coating, aluminum anodizing is at its most vulnerable state when exposed to very high- and very low-pH chemicals. While it will successfully withstand many less-aggressive chemistries, strong acids and bases are its “Achilles’ heel.” The chemical reaction that occurs when anodic coatings are exposed to these chemistries will, by nature, begin to dissolve the anodic coating until the aluminum is left exposed. However, the reaction does not stop there, as the aluminum itself is highly reactive and a cycle of corrosion continues until the part is fully compromised.
The results of such a situation will be the removal of all, or a significant part, of the coating itself, as well as any markings and graphics that may be present. This situation renders the product useless if it is an instrument—and is not much better for cases and trays.
Exploring Alternatives to Aluminum Anodizing for Reusable Medical Devices
To combat the undesirable effects of this newly created problem, the call went out for better performing materials and/or finishes. While manufacturers loved the ease of manufacturing aluminum and the cosmetic attributes of anodizing, the newly arisen problem of degradation of the coating during cleaning created a concern large enough to be placed on high priority. Initially, many ideas were investigated, and some were even launched with little test data; all the while, aluminum and anodizing were still being widely used, though its combined performance was beginning to be criticized.
Alternative materials and their challenges:
- Stainless Steel Medical Cases and Trays: problems with weight, cosmetic finishes, markings
- Nylon Coatings: inability to dry, creating cleanliness concerns; delamination, which also caused clogged nozzles in the washers
- Titanium: limited color options, does not hold color well, expensive
- Plastics: appearance, perceived quality, feel, varying issues regarding manufacturing
There have been very few materials or coatings that have shown to be a better choice than anodized aluminum. Anodizing continues to be the top choice for manufacturers, but it doesn’t mean they are happy about the performance shortcomings or have given up finding a better solution.
The imperative before us became a call-to-action, as members of the aluminum and anodizing industries, to:
- Protect a market that clearly sees the benefits of the products we sell
- Close the gap between performance and need
We had to act when it became evident that the trend in the market was shifting towards finding alternatives to aluminum anodizing on cases, trays, instruments, and reusable component medical parts. The reality was that the developing problem concerning anodized aluminum needed to be solved—and quickly.
To understand the breadth and depth of the issue, we conducted a series of investigations and interviews. We gathered information across North America and Europe from anodize companies, machine shops, contract manufacturers, OEMs, and hospital staff and doctors, to determine what the scope and depth of this problem really was.
We needed to know:
- What did the “real monster” look like and how was the problem being perceived and framed? Was there more than one monster?
- Was this an anodize industry issue?
- An OEM issue?
We discovered that there were a lack of defined performance criteria and testing protocols suitable for the intended use of the articles, coupled with significant in-field variation in cleaning and sterilization methods. In fact, the overarching response indicated that many companies did no performance testing, but relied on irrelevant specifications; and to the degree companies did life-time simulation testing, there were so many different procedures and methods for cleaning, sterilizing, disinfecting, etc., that there could be wide variations in results versus in-field experience.
The Two-Fold Truth about the Failing
- Conventional Type II and Type III anodizing was failing because it was being subjected to conditions it could never withstand.
- Manufacturers needed to find better alternatives to achieve the expected life of their products.
The solution needed to include the eventuality that the equipment was going to be sterilized by the methods that were available to each end user and the finish and/or material must tolerate whatever conditions it will be subject to within the working environment, including those considered to be excessively aggressive.
It was clear that anodized equipment was being subjected to a varying degree of treatments—performed with different cleaning agents, at different times, chemical strengths, temperatures, numbers of cycles, etc. Under many of these conditions, conventional aluminum anodize would fail much earlier than the desired product life, sometimes showing significant degradation within the first five cleaning and sterilization cycles. The major link in all of this was that when exposed to high pH and elevated temperatures, anodized aluminum rapidly breaks down. This failure was single-handedly igniting the drive to find alternative materials and/or finishes.
Micro Crystalline Aluminum Oxide
As explained earlier, any attempt to find an “anodizing” cure for this problem needed to begin with the fact that anodizing is an amorphous coating. It, like all amorphous structures, has weak bond strength and random molecular arrangements that are less ordered and less stable than crystalline structures. For example, typically, pharmaceutical companies place emphasis on creating amorphous drugs that can quickly dissolve into the body. Amorphous structures are more easily broken down or dissolved. In this case, the goal was to see if it was possible to create a partial crystallinity in the coating structure, thereby making the coating itself more stable so it could withstand the rigorous demand of repetitive cleaning.
The first challenges to answer concerning creating this type of structure change were: would it be possible, and if so, could we create crystallinity without making the coating completely crystalline? There were already fully-crystalline anodic coatings on the market using extremely expensive methods, and they lost the characteristics that make aluminum anodizing so popular. Without the beneficial attributes of traditional aluminum oxide coatings, having chemical resistance alone wouldn’t be a sufficient result and would not change the search for a substitute. Therefore, the challenge was to keep the beneficial characteristics of the amorphous anodic coating while forming some greater stability for chemical resistance. Hopefully, by creating partial crystallinity.
Initially the focus was simply on finding ways to try and enhance the stability of the coating by employing different, and even multiple, sealing methods. While we saw some better results, we couldn’t claim victory over the major problem: very low and high pH.
After two years of experimentation with many types of chemical reactions and testing the results, we developed a process that possessed a unique solution to the problem of chemical attack. The process maintained the amorphous structure and beneficial characteristics of Type II and Type III anodic coatings, and also was proven to have partial crystallinity throughout the coating. As was the hypothesis, this partial phase change showed that the coating was now able to resist chemical attack for far greater periods of time. When placed in a strong caustic solution, such as sodium hydroxide, which is used extensively in the anodizing industry to rapidly strip anodic coatings, the micro crystalline aluminum oxide (MICRALOX) parts showed no sign of attack, even after the traditionally coated parts were completely stripped in the same bath.
In fact, MICRALOX was so unique that it was granted three U.S. patents, with multiple patents in other countries.
Since the inception of the original MICRALOX, Precision Coating has introduced two sister chemistries to the MICRALOX family: MICRALOX® Ultra and MICRALOX® Lumina.
MICRALOX Ultra
When maximum performance for strong alkaline cleaning is critical to quality, MICRALOX Ultra provides +50X the chemical resistance compared to decorative Type II anodizing. Aluminum parts coated with MICRALOX Ultra can withstand high-pH cleaning and sterilization protocols commonly used in European markets. MICRALOX Ultra coated parts can also withstand many other aggressive environments that would otherwise strip conventional anodic coatings and subject the parts to extensive corrosion.
MICRALOX Lumina
The clear, translucent oxide of MICRALOX Lumina provides a perfect balance of breakthrough chemical resistance and design flexibility for medical device applications. Whether left natural, or dyed one of nine vivid colors, MICRALOX Lumina coatings achieves up to 50X the resistance in a hot alkaline strip test compared to Type II decorative anodizing. Unlike conventional anodizing and hard coat, the partially crystalline anodic coatings of MICRALOX Lumina hold up over a life-time of regular cleaning and sterilization without fading, chalking, or corroding.
As with all MICRALOX coatings, MICRALOX Ultra and MICRALOX Lumina can receive embedded Sanford Print for crisp, permanent markings that do not delaminate, fade, or chip. This combination of superior chemical- and corrosion-resistant coating and non-destructive markings provides assurance for a full life-time of stringent cleaning and sterilization, as required of all medical devices.
>For more information on MICRALOX Ultra performance, download this coating datasheet.
For more information on MICRALOX Lumina performance, download this coating datasheet.
It should be noted that due to the fact that there is only a partial phase change and that all the benefits of aluminum oxide remain, the new anodic coating is not impervious to chemical attack, but does have a far greater ability than traditional anodic coatings to fend off the attack. On average, the feedback is that the MICRALOX coating lasts five to 50 times longer than traditional anodic coatings when exposed to the same conditions. The result is that anodized aluminum for reusable medical products now have significantly higher performance capability and a longer life cycle, especially when subjected to the harsh treatments of the medical world.
Notably, there were two other important side benefits that came with this incredible innovation. The first was that the coating passed 15,000 hours of salt spray exposure without any pitting. This added benefit creates an alternative solution for marine applications as well, and could be a viable candidate to replace chromium-based seals. This could have an important environmental impact.
The second was the discovery that products anodized with this process now passed the Sterrad and Steris sterilization methods without any organic dye fading or discoloration for many popular colors. The ability to pass exposure to hydrogen peroxide, which is the dominant chemical in the Sterrad NX and Steris DO processes, has helped solve one of the biggest performance concerns for anodized aluminum in the North American medical market. Previously, with few exceptions, organic dyes would fade or discolor from even a few exposures and sterilization procedures. This impacts cosmetic appeal and translates into perceived instrument performance issues. Eliminating this problem is a significant event.
What of the marking and graphics problem? Having the finish be more chemically stable certainly isn’t helping the areas that are being laser or mechanically engraved through the finish. And it isn’t making silk screening to the surface of the product stronger or more resistant to delamination. These types of marking have their place, but could now become the weak link in the chain of producing durable reusable medical products due to the need to maintain traceability of the product and instructions over the product’s life cycle.
Understanding this problem, we can now employ a method of printing “into” the anodic coating before doing the phase change. The “embedded” printing is done by putting specialized dyes into the pores of the anodic coating. These dyes can be specifically placed by several methods and can create varying images. Logos, instructions, safety concerns, etc. can now all be encapsulated within the anodic coating. After sealing and phase change, the markings are permanent. Only complete destruction of the coating can destroy the markings. Given the new performance advancements available with micro crystalline aluminum oxide, the markings can be there through the life of the device, case, instrument, or tray. Problem solved.
With this revolutionary anodic coating on the market for use on reusable cases, trays, tools, and components, the impact on the medical industry has been transformational. Engineers, buyers, and industry leaders who learn of the MICRALOX’s coating capability realize it is an easy substitute for traditional anodic coatings. More tests have been performed and use and demand continues to grow as more OEMs are specifying the finish on their prints.
Since MICRALOX is still classified as an aluminum anodizing, there are no major hurdles that have to be jumped to get approvals on its use. It is simply a better performing aluminum oxide coating! Because it retains the characteristics of Type II and III anodize, MICRALOX is the coating of choice in the medical device industry. Those characteristics such as dye-ability, hardness, thickness, and electrical insulation, along with cytotoxicity compatibility, etc. have made changing finishing specifications easy and quick. Adding embedded printing to these positive features makes the issues facing the medical industry far less intrusive.
What began as an exploration into a problem became a transformational solution with the creation of a revolutionary new product impacting the anodizing world and improving outcomes in the medical sector.
There is actually more to this discussion, which is available for download here.
